1
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Grau BW, Kumar P, Nilsen A, Malhotra SV. Nitrogen-bridgehead compounds: overview, synthesis, and outlook on applications. Org Biomol Chem 2025; 23:1479-1532. [PMID: 39623962 DOI: 10.1039/d4ob01589d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2025]
Abstract
The nitrogen-bridgehead is a common structural motif present in a multitude of natural products. As many of these abundant compounds exhibit biological activities, e.g. against cancer or bacteria, these derivatives are of high interest. While natural products are often associated with problematic characteristics, such as elaborate separation processes, high molecular complexity and limited room for derivatization, purely synthetic approaches can overcome these challenges. Many synthetic procedures have been reported for preparation of artificial nitrogen bridgehead compounds, however, to our surprise only a fraction of these has been tested for their bioactivity. This review is therefore meant to give an overview of existing synthetic methods that provide scaffolds containing bridgehead nitrogen atoms, covering the period from 2000 to 2023. Reviews which cover subunits of this topic are referenced as well.
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Affiliation(s)
- Benedikt W Grau
- Department of Cell, Development and Cancer Biology, Knight Cancer Institute, Oregon Health & Science University, Portland, OR, USA.
- Center for Experimental Therapeutics, Knight Cancer Institute, Oregon Health & Science University, Portland, OR, USA
| | - Praveen Kumar
- Department of Cell, Development and Cancer Biology, Knight Cancer Institute, Oregon Health & Science University, Portland, OR, USA.
- Center for Experimental Therapeutics, Knight Cancer Institute, Oregon Health & Science University, Portland, OR, USA
| | - Aaron Nilsen
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, USA
| | - Sanjay V Malhotra
- Department of Cell, Development and Cancer Biology, Knight Cancer Institute, Oregon Health & Science University, Portland, OR, USA.
- Center for Experimental Therapeutics, Knight Cancer Institute, Oregon Health & Science University, Portland, OR, USA
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2
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Ippoliti FM, Wonilowicz LG, Adamson NJ, Darzi ER, Donaldson JS, Nasrallah DJ, Mehta MM, Kelleghan AV, Houk KN, Garg NK. Total Synthesis of Lissodendoric Acid A. Angew Chem Int Ed Engl 2024; 63:e202406676. [PMID: 38695853 PMCID: PMC11461081 DOI: 10.1002/anie.202406676] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2024] [Indexed: 07/04/2024]
Abstract
We describe a full account of our synthetic strategy leading to the first total synthesis of the manzamine alkaloid lissodendoric acid A . These efforts demonstrate that strained cyclic allenes are valuable synthetic building blocks and can be employed efficiently in total synthesis.
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Affiliation(s)
- Francesca M Ippoliti
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
- Department of Chemistry, Hamline University, St. Paul, Minnesota, 55104, USA
| | - Laura G Wonilowicz
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Nathan J Adamson
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
- Department of Discovery Chemistry, Genentech, Inc., South San Francisco, CA 94080, USA
| | - Evan R Darzi
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
- ElectraTect, Inc., Phoenix, AZ 85004, USA
| | - Joyann S Donaldson
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
- Pfizer Oncology Medicinal Chemistry, San Diego, CA 92121, USA
| | - Daniel J Nasrallah
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
- Department of Chemistry, Roanoke College, Salem, Virginia, 24153, USA
| | - Milauni M Mehta
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
- Small Molecule Therapeutic Discovery, Amgen Research, Amgen Inc., Thousand Oaks, CA 91320, USA
| | - Andrew V Kelleghan
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
- Gilead Sciences Medicinal Chemistry, Foster City, CA 94404, USA
| | - K N Houk
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Neil K Garg
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
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3
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Wonilowicz LG, Mehta MM, Kamecke L, French SA, Garg NK. Diels-Alder Cycloadditions of Oxacyclic Allenes and α-Pyrones. Org Lett 2024; 26:6465-6470. [PMID: 39046907 PMCID: PMC11459240 DOI: 10.1021/acs.orglett.4c02294] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/27/2024]
Abstract
Reactions of α-pyrones with oxacyclic allenes in Diels-Alder trappings are described. We investigate regioselectivity trends and perform competition experiments to assess the influence of structural and electronic features on relative reaction rates. We also demonstrate the stereospecific trapping of an oxacyclic allene, which proceeds in high optical yield. This study provides insight into strained cyclic allene reactivity, as well as new synthetic tools for the rapid construction of complex, heterocyclic scaffolds.
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Affiliation(s)
| | | | - Lisa Kamecke
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, United States
| | - Sarah A. French
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, United States
| | - Neil K. Garg
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, United States
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4
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McVeigh MS, Sorrentino JP, Hands AT, Garg NK. Access to Complex Scaffolds Through [2 + 2] Cycloadditions of Strained Cyclic Allenes. J Am Chem Soc 2024; 146:15420-15427. [PMID: 38768558 PMCID: PMC11459239 DOI: 10.1021/jacs.4c03369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/22/2024]
Abstract
We report the strain-induced [2 + 2] cycloadditions of cyclic allenes for the assembly of highly substituted cyclobutanes. By judicious choice of trapping agent, complex scaffolds bearing heteroatoms, fused rings, contiguous stereocenters, spirocycles, and quaternary centers are ultimately accessible. Moreover, we show that the resulting cycloadducts can undergo thermal isomerization. This study provides an alternative strategy to photochemical [2 + 2] cycloadditions for accessing highly functionalized cyclobutanes, while validating the use of underexplored strained intermediates for the assembly of complex architectures.
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Affiliation(s)
- Matthew S McVeigh
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Jacob P Sorrentino
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Allison T Hands
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Neil K Garg
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
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5
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Zhang YP, Du S, Ma Y, Zhan W, Chen W, Yang X, Zhang H. Structure-Unit-Based Total Synthesis of (-)-Sinulochmodin C. Angew Chem Int Ed Engl 2024; 63:e202315481. [PMID: 38009457 DOI: 10.1002/anie.202315481] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2023] [Revised: 11/21/2023] [Accepted: 11/24/2023] [Indexed: 11/28/2023]
Abstract
Herein we report a structure-unit-based asymmetric total synthesis of sinulochmodin C, a norcembranoid diterpenoid bearing a transannular strained ether bridge β-keto tetrahydrofuran moiety. Our synthetic route features an intramolecular double Michael addition to construct stereospecifically the [7,6,5,5] tetracyclic skeleton, a vinylogous hydroxylation/oxidation procedure or a stereospecific epoxide opening/oxidation sequence to establish the γ-keto enone intermediate, a Lewis acid/Brønsted acid mediated transannular oxa-Michael addition to fuse the β-keto tetrahydrofuran moiety, a Mukaiyama hydration/Pd-C hydrogenation to reverse the C1-configuration of the isopropenyl unit, and a bioinspired transformation of sinulochmodin C into scabrolide A.
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Affiliation(s)
- Yi-Peng Zhang
- Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry of Education, Yunnan Provincial Center for Research and Development of Natural Products, Yunnan Characteristic Plant Extraction Laboratory, School of Pharmacy, Yunnan University, Kunming, 650091, P. R. China
| | - Shufei Du
- Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry of Education, Yunnan Provincial Center for Research and Development of Natural Products, Yunnan Characteristic Plant Extraction Laboratory, School of Pharmacy, Yunnan University, Kunming, 650091, P. R. China
| | - Ying Ma
- Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry of Education, Yunnan Provincial Center for Research and Development of Natural Products, Yunnan Characteristic Plant Extraction Laboratory, School of Pharmacy, Yunnan University, Kunming, 650091, P. R. China
| | - Weixin Zhan
- Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry of Education, Yunnan Provincial Center for Research and Development of Natural Products, Yunnan Characteristic Plant Extraction Laboratory, School of Pharmacy, Yunnan University, Kunming, 650091, P. R. China
| | - Wen Chen
- Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry of Education, Yunnan Provincial Center for Research and Development of Natural Products, Yunnan Characteristic Plant Extraction Laboratory, School of Pharmacy, Yunnan University, Kunming, 650091, P. R. China
| | - Xiaodong Yang
- Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry of Education, Yunnan Provincial Center for Research and Development of Natural Products, Yunnan Characteristic Plant Extraction Laboratory, School of Pharmacy, Yunnan University, Kunming, 650091, P. R. China
| | - Hongbin Zhang
- Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry of Education, Yunnan Provincial Center for Research and Development of Natural Products, Yunnan Characteristic Plant Extraction Laboratory, School of Pharmacy, Yunnan University, Kunming, 650091, P. R. China
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6
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Jankovic CL, McIntosh KC, Lofstrand VA, West FG. Stereoselective Intramolecular [2+2] Trapping of 1,2-Cyclohexadienes: a Route to Rigid, Angularly Fused Tricyclic Scaffolds. Chemistry 2023; 29:e202301668. [PMID: 37352092 DOI: 10.1002/chem.202301668] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2023] [Revised: 06/22/2023] [Accepted: 06/23/2023] [Indexed: 06/25/2023]
Abstract
1,2-Cyclohexadienes generated under mild fluoride-mediated desilylative conditions undergo efficient intramolecular [2+2] trapping, providing tricyclic alkylidene cyclobutanes with complete diastereoselectivity for the cis-fused products. Pendent styrenes or electron-deficient olefins can trap simple 1,2-cyclohexadienes or their oxygenated counterparts, with 14 substrates being disclosed. Reactions proceed at ambient temperature using just cesium fluoride in up to 91 % yield, and the necessary precursors are easily accessed from substituted 2-bromocyclohexenones. Multiple synthetic routes have been developed to install the appropriate functional groups required for [2+2] trapping.
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Affiliation(s)
| | - Kyle C McIntosh
- Department of Chemistry, University of Alberta, Edmonton, AB, T6G 2G2, Canada
| | - Verner A Lofstrand
- Department of Chemistry, University of Alberta, Edmonton, AB, T6G 2G2, Canada
| | - F G West
- Department of Chemistry, University of Alberta, Edmonton, AB, T6G 2G2, Canada
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7
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Mehta MM, Gonzalez JAM, Bachman JL, Garg NK. Cyclic Allene Approach to the Manzamine Alkaloid Keramaphidin B. Org Lett 2023; 25:5553-5557. [PMID: 37387644 PMCID: PMC10460088 DOI: 10.1021/acs.orglett.3c01489] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/01/2023]
Abstract
We report an approach to the core of the manzamine alkaloid keramaphidin B that relies on the strain-promoted cycloaddition of an azacyclic allene with a pyrone trapping partner. The cycloaddition is tolerant of nitrile and primary amide functional groups and can be complemented with a subsequent retro-Diels-Alder step. These efforts demonstrate that strained cyclic allenes can be used to build significant structural complexity and should encourage further studies of these fleeting intermediates.
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Affiliation(s)
- Milauni M Mehta
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, United States
| | - Jordan A M Gonzalez
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, United States
| | - James L Bachman
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, United States
| | - Neil K Garg
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, United States
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8
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Witkowski DC, McVeigh MS, Scherer GM, Anthony SM, Garg NK. Catalyst-Controlled Annulations of Strained Cyclic Allenes with π-Allylpalladium Complexes. J Am Chem Soc 2023; 145:10491-10496. [PMID: 37141000 PMCID: PMC10460090 DOI: 10.1021/jacs.3c03102] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Strained cyclic allenes are a class of in situ-generated fleeting intermediates that, despite being discovered more than 50 years ago, has received significantly less attention from the synthetic community compared to related strained intermediates. Examples of trapping strained cyclic allenes that involve transition metal catalysis are especially rare. We report the first annulations of highly reactive cyclic allenes with in situ-generated π-allylpalladium species. By varying the ligand employed, either of two isomeric polycyclic scaffolds can be obtained with high selectivity. The products are heterocyclic and sp3-rich and bear two or three new stereocenters. This study should encourage the further development of fragment couplings that rely on transition metal catalysis and strained cyclic allenes for the rapid assembly of complex scaffolds.
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Affiliation(s)
- Dominick C Witkowski
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Matthew S McVeigh
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Georgia M Scherer
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Sarah M Anthony
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Neil K Garg
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
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9
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Jankovic CL, West FG. 2 + 2 Trapping of Acyloxy-1,2-cyclohexadienes with Styrenes and Electron-Deficient Olefins. Org Lett 2022; 24:9497-9501. [PMID: 36519787 DOI: 10.1021/acs.orglett.2c03978] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Oxygenated-1,2-cyclohexadienes and their unsubstituted counterpart can be generated under mild conditions by fluoride-induced desilylation and undergo intermolecular [2 + 2]-cycloaddition reactions with a variety of alkene traps to afford bicyclo[4.2.0]octenes. Both styrenes and electron-deficient olefins react in good conversion and with complete regioselectivity in favor of cyclobutane formation at the unsubstituted C2/C3 carbons of the C1-substituted cyclic allenes. Diastereoselectivities are modest (1.1-5.7:1) with a preference for the exo-isomer.
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Affiliation(s)
- Christian L Jankovic
- Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
| | - F G West
- Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
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10
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Abstract
Strained intermediates such as cyclic alkynes and allenes are most commonly utilized in nucleophilic additions and cycloadditions, but have seen increased use in a third area of reactivity: metal-mediated transformations. The merger of strained intermediates and metal catalysis has enabled rapid access to complex, polycyclic systems. Following a discussion of relevant landmark studies involving metals and strained intermediates, this article highlights recent advances in transition metal-mediated transformations from our laboratory. Specifically, this includes the use of arynes in the synthesis of decorated organometallic complexes, and the utilization of cyclic allenes to access enantioenriched heterocycles. Moreover, the broad applicability of such transformations, and exciting future areas of research are discussed.
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Affiliation(s)
- Katie A. Spence
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA, 90095, USA
- These authors contributed equally: Katie A. Spence and Arismel Tena Meza
| | - Arismel Tena Meza
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA, 90095, USA
- These authors contributed equally: Katie A. Spence and Arismel Tena Meza
| | - Neil K. Garg
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA, 90095, USA
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11
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Gorantla SMNVT, Mondal KC. Uncovering the hidden reactivity of benzyne/aryne precursors utilized under milder condition: Bonding and stability studies by EDA-NOCV analyses. J Comput Chem 2022; 43:1543-1560. [PMID: 35861589 DOI: 10.1002/jcc.26956] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Revised: 06/01/2022] [Accepted: 06/02/2022] [Indexed: 11/12/2022]
Abstract
Arenes [C6 H3 R(TMS)(OTf); also called benzyne/aryne precursors] containing inter-related leaving groups Me3 Si (TMS) and CF3 SO3 (OTf) on the adjacent positions (1,2-position) are generally converted to their corresponding aryne-intermediates via the addition of fluoride anion (F- ) and subsequent elimination of TMS and OTf groups. This reaction is believed to proceed via the formation of an anionic intermediate [C6 H4 (TMS-F)(OTf)]- . The EDA-NOCV analysis (EDA-NOCV = energy decomposition analysis-natural orbital for chemical valence) of over 35 such precursors of varied types have been reported to reveal bonding and stability of CAr Si and COTf bonds. EDA-NOCV showed that the nature of the CAr Si bond of C6 H3 R(TMS)(OTf) can be expressed as both dative and electron sharing [CAr Si, CAr →Si]. The CAr OTf bond, on the other hand, can be described explicitly as dative [CAr ←OTf]. The nature of CAr Si bond of [C6 H4 (TMS-F)(OTf)]- exclusively changes to covalent dative σ-bond CAr →S(Me)3F on the attachment of F- to the TMS group of C6 H4 (TMS)(OTf). Introduction of σ-electron withdrawing group (like OMe, NMe2 , and NO2 ) to the ortho-position of the TMS group of functionalized arynes C6 H3 R(TMS)(OTf) prefer to have a covalent dative σ-bond (CAr →Si) over an electron-sharing covalent σ-bond (CAr Si). If this σ-electron withdrawing group is shifted from ortho-position to meta- and para-positions, then the preference for a dative bond decreases significantly, implying that the electronic effect on the nature of chemical bonds affects through bond paths. This effect dies with distance, similar to the well-known inductive effect.
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12
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Abstract
Transient strained cyclic intermediates, such as strained cyclic allenes, are useful building blocks for the synthesis of structurally and stereochemically complex scaffolds. Trappings of strained cyclic allenes are thought to occur primarily through either two or one electron processes. Regarding the latter, diradical intermediates have been invoked in (2 + 2) cycloadditions and (3 + 2) nitrone cycloadditions. The present study questions if a monoradical pathway could exist for strained cyclic allene reactivity, as examined in the reaction of 1,2-cyclohexadiene and TEMPO radical. Our findings suggest the viability of this monoradical pathway.
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Affiliation(s)
- Matthew S. McVeigh
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, United States
| | - Neil K. Garg
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, United States
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13
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Efremova MM, Makarova AA, Novikov AS, Kryukova MA, Kuznetsov MA, Molchanov AP. Regio- and stereoselective (3 + 2)-cycloaddition reactions of nitrones with cyclic allenes. Org Biomol Chem 2021; 19:9773-9784. [PMID: 34730596 DOI: 10.1039/d1ob01584b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
An effective approach to access functionalized 2H-cyclonona(deca)[d]isoxazoles and 15-oxo-3,10-methanobenzo[b][1]azacyclododecines has been developed by the reaction of N-aryl-C,C-bis(methoxycarbonyl)nitrones with cyclonona(deca)-1,2-dienes in a one-pot fashion. The reaction of N-aryl-C-(phenylcarbamoyl)nitrones with these allenes proceeds strictly regioselectively giving the mixtures of diastereomeric isoxazolidines containing a double bond at the C4-position of the isoxazolidine ring. The quantum chemical calculations show that the regioselectivity of these reactions is in good agreement with the reactivity indices of the considered compounds.
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Affiliation(s)
- Mariia M Efremova
- Institute of Chemistry, Saint Petersburg State University (SPbU), Universitetskaya nab. 7/9, Saint Petersburg 199034, Russia.
| | - Anastasia A Makarova
- Institute of Chemistry, Saint Petersburg State University (SPbU), Universitetskaya nab. 7/9, Saint Petersburg 199034, Russia.
| | - Alexander S Novikov
- Institute of Chemistry, Saint Petersburg State University (SPbU), Universitetskaya nab. 7/9, Saint Petersburg 199034, Russia.
| | - Mariya A Kryukova
- Institute of Chemistry, Saint Petersburg State University (SPbU), Universitetskaya nab. 7/9, Saint Petersburg 199034, Russia.
| | - Mikhail A Kuznetsov
- Institute of Chemistry, Saint Petersburg State University (SPbU), Universitetskaya nab. 7/9, Saint Petersburg 199034, Russia.
| | - Alexander P Molchanov
- Institute of Chemistry, Saint Petersburg State University (SPbU), Universitetskaya nab. 7/9, Saint Petersburg 199034, Russia.
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14
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Anthony S, Wonilowicz LG, McVeigh MS, Garg NK. Leveraging Fleeting Strained Intermediates to Access Complex Scaffolds. JACS AU 2021; 1:897-912. [PMID: 34337603 PMCID: PMC8317162 DOI: 10.1021/jacsau.1c00214] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Indexed: 05/07/2023]
Abstract
Arynes, strained cyclic alkynes, and strained cyclic allenes were validated as plausible intermediates in the 1950s and 1960s. Despite initially being considered mere scientific curiosities, these transient and highly reactive species have now become valuable synthetic building blocks. This Perspective highlights recent advances in the field that have allowed access to structural and stereochemical complexity, including recent breakthroughs in asymmetric catalysis.
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15
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Kelleghan AV, Witkowski DC, McVeigh MS, Garg NK. Palladium-Catalyzed Annulations of Strained Cyclic Allenes. J Am Chem Soc 2021; 143:9338-9342. [PMID: 34143634 PMCID: PMC8290222 DOI: 10.1021/jacs.1c04896] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report Pd-catalyzed annulations of in situ generated strained cyclic allenes. This methodology employs aryl halides and cyclic allene precursors as the reaction partners in order to generate fused heterocyclic products. The annulation proceeds via the formation of two new bonds and an sp3 center. Moreover, both diastereo- and enantioselective variants of this methodology are validated, with the latter ultimately enabling the rapid enantioselective synthesis of a complex hexacyclic product. Studies leveraging transition metal catalysis to intercept cyclic allenes represent a departure from the more common, historical modes of cyclic allene trapping that rely on nucleophiles or cycloaddition partners. As such, this study is expected to fuel the development of reactions that strategically merge transition metal catalysis and transient strained intermediate chemistry for the synthesis of complex scaffolds.
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Affiliation(s)
- Andrew V Kelleghan
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Dominick C Witkowski
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Matthew S McVeigh
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Neil K Garg
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
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16
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Ramirez M, Svatunek D, Liu F, Garg NK, Houk KN. Origins of
Endo
Selectivity in Diels–Alder Reactions of Cyclic Allene Dienophiles. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202101809] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Melissa Ramirez
- Department of Chemistry and Biochemistry University of California, Los Angeles Los Angeles CA 90095 USA
| | - Dennis Svatunek
- Department of Chemistry and Biochemistry University of California, Los Angeles Los Angeles CA 90095 USA
| | - Fang Liu
- College of Sciences Nanjing Agricultural University Nanjing 210095 China
| | - Neil K. Garg
- Department of Chemistry and Biochemistry University of California, Los Angeles Los Angeles CA 90095 USA
| | - Kendall N. Houk
- Department of Chemistry and Biochemistry University of California, Los Angeles Los Angeles CA 90095 USA
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17
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Ramirez M, Svatunek D, Liu F, Garg NK, Houk KN. Origins of Endo Selectivity in Diels-Alder Reactions of Cyclic Allene Dienophiles. Angew Chem Int Ed Engl 2021; 60:14989-14997. [PMID: 33851504 DOI: 10.1002/anie.202101809] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2021] [Revised: 03/20/2021] [Indexed: 11/08/2022]
Abstract
Strained cyclic allenes, first discovered in 1966 by Wittig and co-workers, have recently emerged as valuable synthetic building blocks. Previous experimental investigations, and computations reported here, demonstrate that the Diels-Alder reactions of furans and pyrroles with 1,2-cyclohexadiene and oxa- and azaheterocyclic analogs proceed with endo selectivity. This endo selectivity gives the adduct with the allylic saturated carbon of the cyclic allene endo to the diene carbons. The selectivity is very general and useful in synthetic applications. Our computational study establishes the origins of this endo selectivity. We analyze the helical frontier molecular orbitals of strained cyclic allenes and show how secondary orbital and electrostatic effects influence stereoselectivity. The LUMO of carbon-3 of the allene (C-3 is not involved in primary orbital interactions) interacts in a stabilizing fashion with the HOMO of the diene in such a way that the carbon of the cyclic allene attached to C-1 favors the endo position in the transition state. The furan LUMO, allene HOMO interaction reinforces this preference. These mechanistic studies are expected to prompt the further use of long-avoided strained cyclic allenes in chemical synthesis.
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Affiliation(s)
- Melissa Ramirez
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Dennis Svatunek
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Fang Liu
- College of Sciences, Nanjing Agricultural University, Nanjing, 210095, China
| | - Neil K Garg
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Kendall N Houk
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA, 90095, USA
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18
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Zhang J, Xie Z. Tandem [4 + 2]/[2 + 2] cycloaddition of o-carboryne with enynes: facile construction of carborane-fused tricyclics. Chem Sci 2021; 12:5616-5620. [PMID: 34168796 PMCID: PMC8179614 DOI: 10.1039/d0sc07047e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2020] [Accepted: 02/19/2021] [Indexed: 11/21/2022] Open
Abstract
o-Carboryne (1,2-dehydro-o-carborane) is a very useful synthon for the synthesis of a variety of carborane-functionalized molecules. With 1-Li-2-OTf-o-C2B10H10 as the precursor, o-carboryne undergoes an efficient [4 + 2] cycloaddition with various conjugated enynes, followed by a subsequent [2 + 2] cycloaddition at room temperature, generating a series of carborane-fused tricyclo[6.4.0.02,7]dodeca-2,12-dienes in moderate to high isolated yields. This reaction is compatible with many functional groups and has a broad substrate scope. A reactive carborane-fused 1,2-cyclohexadiene intermediate is involved, which is supported by experimental results and DFT calculations. This protocol offers a convenient strategy for the construction of complex carborane-functionalized tricyclics.
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Affiliation(s)
- Jie Zhang
- Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The Chinese University of Hong Kong Shatin, N. T. Hong Kong China
| | - Zuowei Xie
- Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The Chinese University of Hong Kong Shatin, N. T. Hong Kong China
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19
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Wang B, Constantin MG, Singh S, Zhou Y, Davis RL, West FG. Generation and trapping of electron-deficient 1,2-cyclohexadienes. Unexpected hetero-Diels-Alder reactivity. Org Biomol Chem 2021; 19:399-405. [PMID: 33300539 DOI: 10.1039/d0ob02285c] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Keto-substituted 1,2-cyclohexadienes were generated by base-mediated (KOt-Bu) elimination, and found to dimerize via an unprecedented formal hetero-Diels-Alder process, followed by hydration. These highly reactive cyclic allene intermediates were also trapped in Diels-Alder reactions by furan, 2,5-dimethylfuran, or diphenylisobenzofuran to afford cycloadducts with high regio- and diastereoselectivity, and could also be intercepted in a hetero-Diels-Alder process with enamine dienophiles. Endo/exo stereochemistry was unambiguously determined via X-ray crystallography in the case of nitrile-substituted 1,2-cyclohexadiene. DFT calculations indicate that the novel hetero-Diels-Alder processes observed with these allenes occur via a concerted asynchronous cycloaddition mechanism.
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Affiliation(s)
- Baolei Wang
- Department of Chemistry, University of Alberta, E3-43 Gunning-Lemieux Chemistry Centre, Edmonton, AB, Canada T6G 2G2. and State-Key Laboratory of Elemento-Organic Chemistry, Collaborative Innovation Center of Chemical Science and Engineering, College of Chemistry, Nankai University, Tianjin 300071, P. R. China
| | - Marius-Georgian Constantin
- Department of Chemistry, University of Alberta, E3-43 Gunning-Lemieux Chemistry Centre, Edmonton, AB, Canada T6G 2G2.
| | - Simarpreet Singh
- Department of Chemistry, University of Manitoba, 360 Parker Bldg., 144 Dysart Rd., Winnipeg, MN, Canada R3T 2N2
| | - Yuqiao Zhou
- Department of Chemistry, University of Alberta, E3-43 Gunning-Lemieux Chemistry Centre, Edmonton, AB, Canada T6G 2G2.
| | - Rebecca L Davis
- Department of Chemistry, University of Manitoba, 360 Parker Bldg., 144 Dysart Rd., Winnipeg, MN, Canada R3T 2N2
| | - F G West
- Department of Chemistry, University of Alberta, E3-43 Gunning-Lemieux Chemistry Centre, Edmonton, AB, Canada T6G 2G2.
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