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Silver-Catalyzed Tandem Cycloisomerization/[5 + 2] Cycloaddition of 3-Cyclopropylideneprop-2-en-1-ones with Oxidopyrylium Ylides to Form Bibridged Benzocycloheptanones. J Org Chem 2023. [PMID: 37364091 DOI: 10.1021/acs.joc.3c00436] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/28/2023]
Abstract
Herein, we report a mild, one-pot method for silver-catalyzed tandem cycloisomerization/[5 + 2] cycloaddition reactions between readily accessible cyclopropyl-tethered allenyl ketones and benzopyranone-derived oxidopyrylium ylides. The reactions proceed via a cyclobutene-fused furan intermediate generated in situ by a cycloisomerization/1,2-carbene transfer/ring-expansion cascade. This method, which features an unprecedented formal [5 + 2] cycloaddition, delivers good to excellent yields of structurally complex bibridged benzocycloheptanones bearing a strained cyclobutane ring and an O-bridged ring.
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2
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Heimionones A-E, New Sesquiterpenoids Produced by Heimiomyces sp., a Basidiomycete Collected in Africa. Molecules 2023; 28:molecules28093723. [PMID: 37175133 PMCID: PMC10179880 DOI: 10.3390/molecules28093723] [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: 04/04/2023] [Revised: 04/19/2023] [Accepted: 04/24/2023] [Indexed: 05/15/2023] Open
Abstract
With heimionones A-E (1-5), five new terpenoids were isolated from submerged cultures of Heimiomyces sp. in addition to the previously described compounds hispidin, hypholomin B, and heimiomycins A and B. Planar structures of the metabolites were elucidated by 1D and 2D NMR in addition to HRESIMS data. While ROESY data assigned relative configurations, absolute configurations were determined by the synthesis of MTPA esters of 1, 3, and 5. The [6.3.0] undecane core structure of compounds 3-5 is of the asteriscane-type, however, the scaffold of 1 and 2 with their bicyclo [5.3.0] decane core and germinal methyl substitution is, to our knowledge, unprecedented. Together with several new compounds that were previously isolated from solid cultures of this strain, Heimiomyces sp. showed an exceptionally high chemical diversity of its secondary metabolite profile.
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3
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Stereoselective (4 + 3) cycloadditions of allenyl ethers-furans by chiral auxiliaries inducing and evaluation of anti-breast cancer activity. FRONTIERS IN PLANT SCIENCE 2022; 13:1087899. [PMID: 36618658 PMCID: PMC9812524 DOI: 10.3389/fpls.2022.1087899] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Accepted: 11/14/2022] [Indexed: 06/17/2023]
Abstract
The medicinal plants were wildly library of natural products in drug discovery. The most active molecules with seven-membered rings skeleton represent a challenge for construction. A stereoselectivity (4 + 3) cycloadditions between allenyl ethers and substituted furans induced by chiral auxiliaries has been investigated. And the results showed significant stereoselectivities and regioselectivities. The optical cycloadducts with an oxygen-substituted seven-membered ring framework were generated by removing chiral auxiliaries under acidic conditions. The antiproliferative activity of the novel compounds displayed moderate antiproliferative effects toward T47D cells.
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4
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Asymmetric syntheses of (–)-hedyosumins A–C via enantioselective Diels–Alder reaction of (E)-Hex-3-en-5-yn-2-one and platinum(II)-catalyzed [3+2]-cyclization. Tetrahedron Lett 2022. [DOI: 10.1016/j.tetlet.2022.153946] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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5
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Structures, Occurrences and Biosynthesis of 11,12,13-Tri-nor-Sesquiterpenes, an Intriguing Class of Bioactive Metabolites. PLANTS 2022; 11:plants11060769. [PMID: 35336651 PMCID: PMC8949605 DOI: 10.3390/plants11060769] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Revised: 03/08/2022] [Accepted: 03/10/2022] [Indexed: 12/02/2022]
Abstract
The compounds 11,12,13-tri-nor-sesquiterpenes are degraded sesquiterpenoids which have lost the C3 unit of isopropyl or isopropenyl at C-7 of the sesquiterpene skeleton. The irregular C-backbone originates from the oxidative removal of a C3 side chain from the C15 sesquiterpene, which arises from farnesyl diphosphate (FDP). The C12-framework is generated, generally, in all families of sesquiterpenes by oxidative cleavage of the C3 substituent, with the simultaneous introduction of a double bond. This article reviews the isolation, biosynthesis and biological activity of this special class of sesquiterpenes, the 11,12,13-tri-nor-sesquiterpenes.
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CuCl
2
‐Mediated Oxidative Intramolecular α‐Arylation of Ketones with Phenolic Nucleophiles via Oxy‐Allyl Cation Intermediates. Chem Asian J 2020; 15:3816-3819. [DOI: 10.1002/asia.202001032] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 10/01/2020] [Indexed: 12/12/2022]
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7
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Determination of the Absolute Configurations of Chiral Alkanes – An Analysis of the Available Tools. European J Org Chem 2020. [DOI: 10.1002/ejoc.202000711] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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8
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9
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Brønsted Acid-Catalyzed Intramolecular α-Arylation of Ketones with Phenolic Nucleophiles via Oxy-Allyl Cation Intermediates. European J Org Chem 2020. [DOI: 10.1002/ejoc.202000169] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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10
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Rhodium-Catalyzed (5 + 2) and (5 + 1) Cycloadditions Using 1,4-Enynes as Five-Carbon Building Blocks. Acc Chem Res 2020; 53:231-243. [PMID: 31820914 DOI: 10.1021/acs.accounts.9b00477] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Cycloaddition reactions are a hallmark in organic synthesis because they provide an efficient way to construct highly substituted carbo- and heterocycles found in natural products and pharmaceutical agents. Most cycloadditions occur under thermal or photochemical conditions, but transition-metal complexes can promote reactions that occur beyond these circumstances. Transition-metal complexation with alkynes, alkenes, allenes, or dienes often alters the reactivity of those π-systems and facilitates access to diverse cycloaddition products. This Account describes our efforts toward the design of novel five-carbon synthons for use in rhodium-catalyzed (5 + n) cycloadditions, which include 3-acyloxy-1,4-enynes (ACEs) for (5 + 1) and (5 + 2) cycloadditions and 3-hydroxy-1,4-enynes (HYEs) for (5 + 1) cycloadditions. Furthermore, this Account includes relevant computational information, mechanistic insights, and applications of these cycloadditions in the synthesis of various highly substituted carbo- and heterocycles. The (5 + n) cycloaddition reactions presented herein share the following common mechanistic features: the 1,2-migration of an acyloxy group in propargyl esters or the ionization of a hydroxyl group in propargylic alcohols, oxidative cyclization to form a metallacycle, insertion of the one- or two-carbon component, and reductive elimination to yield the final product. In conjunction with a cationic rhodium catalyst, we used ACEs for the intramolecular (5 + 2) cycloaddition with tethered alkynes, alkenes, and allenes. In some cases, an electron-deficient phosphine ligand improved the reaction yields, especially when the ACE featured an internal alkyne. We also demonstrated that chirality could be efficiently transferred from a relatively simple starting material to a more complex bicyclic product. Products derived from ACEs with tethered alkenes and allenes contained one or more stereocenters, and high diastereoselectivity was achieved in most of these cases. For ACEs tethered to an allene, the reaction preferentially occurred at the internal alkene. We also switched the positions of the alkene and the alkyne in the 1,4-enyne of our original ACE to provide an inverted ACE variant, which produced products with complementary functionalities. After we successfully developed the Rh-catalyzed intramolecular (5 + 2) cycloaddition, we optimized conditions for the intermolecular version, which required a neutral rhodium catalyst and phosphine ligand. When a terminal alkyne was used as the two-carbon component, high regioselectivity was observed. While investigating the effect of esters on the rate of the intermolecular (5 + 2) cycloadditions, we determined that an electron-rich ester significantly accelerated the reaction. Subsequently, we demonstrated that (5 + 1) cycloadditions undergo this rate enhancement as well in the presence of an ester. Aside from ACEs, we synthesized HYEs in four steps from commercially available 2-aminobenzoic acid for use in the (5 + 1) cycloaddition. Mechanistically, HYEs were designed so that the aniline nitrogen could serve as the nucleophile and the -OH could serve as the leaving group. Using HYEs, we developed a novel method to make substituted carbazoles, dibenzofurans, and tricyclic compounds with a cyclohexadienone moiety. Although the occurrence of transition-metal-catalyzed acyloxy migrations has been known for decades, only recently has their synthetic value been realized. We hope our studies that employ readily available 1,4-enynes as the five-carbon components in (5 + n) cycloadditions can inspire the design of new two-component and multicomponent cycloadditions.
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11
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Asymmetric Synthesis of a 5,7-Fused Ring System Enabled by an Intramolecular Buchner Reaction with Chiral Rhodium Catalyst. Org Lett 2019; 21:10081-10084. [PMID: 31808701 DOI: 10.1021/acs.orglett.9b04048] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
A Rh-catalyzed asymmetric intramolecular Buchner ring expansion of α-alkyl-α-diazoesters has been developed. The present protocol generates a 5,7-fused ring system in an enantioselective manner while minimizing β-hydrogen migration, which has been a competing reaction when using α-alkyl-α-diazoesters. The ester functionality at the bridgehead position would be a useful synthetic handle for further derivatization to complex molecules including natural products.
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12
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Divergent Construction of Macrocyclic Alkynes via Catalytic Metal Carbene C(sp2)–H Insertion and the Buchner Reaction. ACS Catal 2019. [DOI: 10.1021/acscatal.9b04199] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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13
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Mechanistic Perspectives in the Regioselective Indole Addition to Unsymmetrical Silyloxyallyl Cations. J Org Chem 2019; 84:7166-7174. [PMID: 31050428 DOI: 10.1021/acs.joc.9b00853] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Our investigations on the reaction mechanism to account for regioselectivity on the addition of indoles to unsymmetrical silyloxyallyl cations are reported. Using both experimental and computational methods, we confirmed the significance of steric effects from the silyl ether group toward directing the inward approach of indoles, leading to nucleophilic attack at the less substituted electrophilic α'-carbon. The role of residual water toward accelerating the rate of reaction is established through stabilization of the participating silyloxyallyl cation.
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14
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Stereoselective and Modular Assembly Method for Heterocycle-Fused Daucane Sesquiterpenoids. Chemistry 2018; 24:13783-13787. [DOI: 10.1002/chem.201803248] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Indexed: 01/31/2023]
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15
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16
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Synthesis of carotol using a formal (4+1)-cycloaddition of chiral dialkoxycarbenes. CAN J CHEM 2018. [DOI: 10.1139/cjc-2017-0594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We report formal intramolecular (4+1)-cycloadditions of dialkoxycarbenes used in the synthesis of the daucane-type sesquiterpene carotol. We found a chiral dialkoxycarbene capable of diastereoselective formation of a key oxabicyclo[3.3.0]octene adduct. Carotol was synthesized in 14 linear steps from simple starting materials.
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17
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Dearomatization of naphthols using oxy-allyl cations: efficient construction of α-all-carbon quaternary center-containing 2-(2-oxocycloalkyl)cycloalkyl diketones. Org Chem Front 2018. [DOI: 10.1039/c8qo00783g] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
An efficient strategy for the dearomatization of both α- and β-naphthols using in situ generated oxy-allyl cations is reported.
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18
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Nazarov Cyclization Entry to Chiral Bicyclo[5.3.0]decanoid Building Blocks and Its Application to Formal Synthesis of (−)-Englerin A. Org Lett 2017; 19:5142-5145. [DOI: 10.1021/acs.orglett.7b02428] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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19
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Enantioselective Oxidative (4+3) Cycloadditions between Allenamides and Furans through Bifunctional Hydrogen-Bonding/Ion-Pairing Interactions. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201704804] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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20
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Enantioselective Oxidative (4+3) Cycloadditions between Allenamides and Furans through Bifunctional Hydrogen-Bonding/Ion-Pairing Interactions. Angew Chem Int Ed Engl 2017; 56:10535-10538. [DOI: 10.1002/anie.201704804] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Revised: 06/24/2017] [Indexed: 12/27/2022]
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21
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Abstract
A total synthesis of the cytotoxic terpenoid hortonone C was accomplished and its absolute stereochemistry confirmed. Intermediate (+)-4 was synthesized using either an asymmetric conjugate addition strategy, or by elaboration of the Hajos-Parrish ketone. Reduction of (+)-4 under dissolving-metal conditions and trapping the enolate intermediate served to control the cis-stereochemistry at the ring fusion and provide a silyl enol ether necessary for ring expansion. Comparison of optical rotation data confirmed that the absolute configuration of natural hortonone C is (6S,7S,10S).
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22
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Abstract
The total synthesis of orientalol F was accomplished in 13 steps using gold-catalyzed tandem cycloisomerization of alkynediol as a key step.
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23
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Intramolecular Parallel [4+3] Cycloadditions of Cyclopropane 1,1-Diesters with [3]Dendralenes: Efficient Construction of [5.3.0]Decane and Corresponding Polycyclic Skeletons. Chemistry 2016; 23:1231-1236. [DOI: 10.1002/chem.201605190] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2016] [Indexed: 12/12/2022]
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24
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Stereocontrolled Syntheses of Seven-Membered Carbocycles by Tandem Allene Aziridination/[4+3] Reaction. Angew Chem Int Ed Engl 2016; 55:13240-13243. [PMID: 27709816 PMCID: PMC5218842 DOI: 10.1002/anie.201606195] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2016] [Indexed: 11/07/2022]
Abstract
A tandem allene aziridination/[4+3]/reduction sequence converts simple homoallenic sulfamates into densely functionalized aminated cycloheptenes, where the relative stereochemistry at five contiguous asymmetric centers can be controlled through the choice of the solvent and the reductant. The products resulting from this chemistry can be readily transformed into complex molecular scaffolds which contain up to seven contiguous stereocenters.
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25
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Stereocontrolled Syntheses of Seven-Membered Carbocycles by Tandem Allene Aziridination/[4+3] Reaction. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201606195] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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26
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Abstract
Dialkoxycarbenes are more reactive than NHCs and participate in many reactions including a formal (4 + 1) cycloaddition with electron-deficient dienes. We have learned to control the relative stereochemistry of the newly created chiral carbons in this process and now report that, combined with a chiral auxiliary, it has been used successfully in a short and efficient synthesis of the sesquiterpene carotol.
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27
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Enantioselective Synthesis of Guaianolides in the Osmitopsin Family by Domino Metathesis. Org Lett 2016; 18:3298-301. [DOI: 10.1021/acs.orglett.6b01619] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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28
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29
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Rhodium‐Catalyzed Intramolecular [5+2] Cycloaddition of Inverted 3‐Acyloxy‐1,4‐enyne and Alkyne: Experimental and Theoretical Studies. Chemistry 2016; 22:7079-83. [DOI: 10.1002/chem.201601195] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2016] [Indexed: 12/31/2022]
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30
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31
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An expedient synthesis of functionalized 1,4-diketone-derived compounds via silyloxyallyl cation intermediates. Chem Commun (Camb) 2016; 52:2300-3. [DOI: 10.1039/c5cc09763k] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Herein we describe the synthesis of highly functionalized 1,4-diketones that are readily differentiated as monosilylenol ethers via direct capture of silyloxyallyl cations by silyl enolates under Brønsted acid catalysis.
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32
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Rhodium-Catalyzed [4+3] Cycloaddition to Furans: Direct Access to Functionalized Bicyclo[5.3.0]decane Derivatives. European J Org Chem 2015. [DOI: 10.1002/ejoc.201501271] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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33
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Cooperative benzylic-oxyallylic stabilized cations: regioselective construction of α-quaternary centers in ketone-derived compounds. Chem Sci 2015; 6:6312-6319. [PMID: 30090249 PMCID: PMC6054113 DOI: 10.1039/c5sc01914a] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Accepted: 07/20/2015] [Indexed: 11/23/2022] Open
Abstract
We describe a novel reactivity of benzylic-stabilized oxyallyl cations towards regioselective construction of carbon quaternary centers. These synthetically useful intermediates were readily generated upon ionization of aryl substituted α-hydroxy methylenol ethers with catalytic, mild Brønsted acid. The emerging unsymmetrical oxyallyl cations were then directly captured by indoles and other nucleophiles with exquisite control of regioselectivity, predictably at the electrophilic carbon bearing the alkyl substituent to produce highly functionalized, value-added enol ethers.
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Rhodium-Catalyzed Stereoselective Intramolecular [5 + 2] Cycloaddition of 3-Acyloxy 1,4-Enyne and Alkene. Org Lett 2015; 17:5128-31. [PMID: 26440751 DOI: 10.1021/acs.orglett.5b02665] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The first rhodium-catalyzed intramolecular [5 + 2] cycloaddition of 3-acyloxy 1,4-enyne and alkene was developed. The cycloaddition is highly diastereoselective in most cases. Various cis-fused bicyclo[5.3.0]decadienes were prepared stereoselectively. The chirality in the propargylic ester starting materials could be transferred to the bicyclic products with high efficiency. Electron-deficient phosphine ligand greatly facilitated the cycloaddition. Up to three new stereogenic centers could be generated. The resulting diene in the products could be hydrolyzed to enones, which allowed the introduction of more functional groups to the seven-membered ring.
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35
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An iodine catalyzed metal free domino process for the stereoselective synthesis of oxygen bridged bicyclic ethers. Org Biomol Chem 2015; 13:6737-41. [PMID: 25994362 DOI: 10.1039/c5ob00518c] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
A domino reaction has been developed for the synthesis of oxygen bridged bicyclic ethers through the coupling of 4-(2-hydroxyethyl)cyclohex-3-enols with aldehydes in the presence of 10 mol% of molecular iodine in dichloromethane at 25 °C. This method is highly diastereoselective affording the corresponding bicyclic ethers, i.e. octahydro-4a,7-epoxyisochromenes in good yields with high selectivity. It is the first report on the synthesis of oxygen bridged bicyclic ethers using a domino Prins strategy.
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36
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Tetrahedron reports on organic chemistry. Tetrahedron 2015. [DOI: 10.1016/s0040-4020(15)00744-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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37
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Synthesis and structural studies of novel fused seven-membered carbocycles derived from exo-2-oxazolidinone dienes through (4+3) cycloadditions. Tetrahedron 2015. [DOI: 10.1016/j.tet.2014.12.065] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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38
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Brønsted Acid Catalyzed α′-Functionalization of Silylenol Ethers with Indoles. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201409758] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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39
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Brønsted Acid Catalyzed α′-Functionalization of Silylenol Ethers with Indoles. Angew Chem Int Ed Engl 2015; 54:4641-5. [DOI: 10.1002/anie.201409758] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2014] [Revised: 01/21/2015] [Indexed: 11/10/2022]
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40
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Catalyst-free formation of 1,4-diketones by addition of silyl enolates to oxyallyl zwitterions in situ generated from α-haloketones. RSC Adv 2015. [DOI: 10.1039/c5ra12244a] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Here we report an efficient and practical method for the preparation of 1,4-diketones by direct coupling of α-haloketones with silyl enolates at room temperature. No catalysts were required in our protocol.
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41
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Preparation of cycloheptane ring by nucleophilic cyclopropanation of 1,2-diketones with bis(iodozincio)methane. Org Biomol Chem 2015; 13:241-7. [DOI: 10.1039/c4ob01474j] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The nucleophlic cyclopropanation of hexa-1,5-diene-3,4-diones with bis(iodozincio)methane afforded the Zn alkoxides of cyclohepta-2,7-diene-1,2-diols stereospecifically via Zn alkoxides of cis-dialkenylcyclopropane-1,2-diols.
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42
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A practical deca-gram scale ring expansion of (R)-(−)-carvone to (R)-(+)-3-methyl-6-isopropenyl-cyclohept-3-enone-1. Org Biomol Chem 2015; 13:7633-42. [DOI: 10.1039/c5ob00525f] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A route to enantiopure (R)-(+)-3-methyl-6-isopropenyl-cyclohept-3-enone-1, an intermediate for terpenoids, has been developed and includes a highly chemo- and regioselective Tiffeneau–Demjanov reaction.
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Synthesis of guaia-4(5)-en-11-ol, guaia-5(6)-en-11-ol, aciphyllene, 1-epi-melicodenones C and E, and other guaiane-type sesquiterpenoids via the diastereoselective epoxidation of guaiol. JOURNAL OF NATURAL PRODUCTS 2014; 77:2522-2536. [PMID: 25330459 DOI: 10.1021/np500611z] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The diastereomeric ratio of epoxidation of the internally bridged carbon-carbon double bond of guaiol (1a) is strongly influenced by the combined effects of the types of remote protecting groups on the hydroxyisopropyl side chain, choice of solvent, and epoxidizing reagent. This observation has allowed us to devise concise stereoselective syntheses of a range of guaiane-type sesquiterpenoids via an epoxidation, ring-opening/elimination, and functionality manipulation sequence. Natural products guaia-4(5)-en-11-ol (2a), guaia-5(6)-en-11-ol (3), and aciphyllene (4a) and epimers of the recently isolated natural products, 1-epi-guaia-4(5)-en-11-ol (2b), 1-epi-aciphyllene (4b), and 1-epi-melicodenones C (5a) and E (6a), were synthesized in good yields in relatively few steps.
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Catalyst and substituent effects on the rhodium(II)-catalysed intramolecular Buchner reaction. Tetrahedron 2014. [DOI: 10.1016/j.tet.2014.07.033] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Unequivocal structural assignments of three cycloheptenoid intermediates for guaiane sesquiterpenes: an experimental and theoretical approach. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2014; 52:318-328. [PMID: 24723362 DOI: 10.1002/mrc.4057] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2013] [Revised: 02/07/2014] [Accepted: 02/11/2014] [Indexed: 06/03/2023]
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The Synthesis of Seven-Membered Rings in Natural Products. ACTA ACUST UNITED AC 2014. [DOI: 10.1016/b978-0-444-63281-4.00014-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
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47
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Efficient catalytic-free method to produce α-aryl cycloalkanones through highly chemoselective coupling of aryl compounds with oxyallyl cations. RSC Adv 2014. [DOI: 10.1039/c4ra01043d] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Efficient catalytic-free method to produce α-aryl cycloalkanones through highly chemoselective coupling of aryl compounds with oxyallyl cations at room temperature.
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A unified approach to the daucane and sphenolobane bicyclo[5.3.0]decane core: enantioselective total syntheses of daucene, daucenal, epoxydaucenal B, and 14-para-anisoyloxydauc-4,8-diene. Chemistry 2013; 19:17745-50. [PMID: 24302464 PMCID: PMC3927641 DOI: 10.1002/chem.201302353] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2013] [Indexed: 11/07/2022]
Abstract
Access to the bicyclo[5.3.0]decane core found in the daucane and sphenolobane terpenoids via a key enone intermediate enables the enantioselective total syntheses of daucene, daucenal, epoxydaucenal B, and 14-para-anisoyloxydauc-4,8-diene. Central aspects include a catalytic asymmetric alkylation followed by a ring contraction and ring-closing metathesis to generate the five- and seven-membered rings, respectively.
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Transfer of chirality in the rhodium-catalyzed intramolecular [5+2] cycloaddition of 3-acyloxy-1,4-enynes (ACEs) and alkynes: synthesis of enantioenriched bicyclo[5.3.0]decatrienes. Angew Chem Int Ed Engl 2013; 52:13601-5. [PMID: 24150975 PMCID: PMC3867534 DOI: 10.1002/anie.201306919] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2013] [Indexed: 12/12/2022]
Abstract
Chiral bicycles: Enantioenriched bicyclo[5.3.0]decatrienes were prepared from readily available chiral 3-acyloxy-1,4-enynes (ACEs) for the first time. In most cases, the chirality of the ACEs could be transferred to the bicyclic products with high efficiency. Inversion of the configuration was observed, thus confirming the predictions of previous computational studies.
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Transfer of Chirality in the Rhodium-Catalyzed Intramolecular [5+2] Cycloaddition of 3-Acyloxy-1,4-enynes (ACEs) and Alkynes: Synthesis of Enantioenriched Bicyclo[5.3.0]decatrienes. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201306919] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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