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Sasmal A, Taniguchi T, Wipf P, Curran DP. Memory of chirality in rebound cyclizations of α-amide radicals. CAN J CHEM 2013. [DOI: 10.1139/v2012-085] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Reduction of (S)-N-(2-bromoallyl)-N-(tert-butyl)-2-methyl-3-phenylpropanamide with tributyltin hydride provides (3S,4S)-3-benzyl-1-(tert-butyl)-3,4-dimethylpyrrolidin-2-one with about 80% retention of chirality at the stereocenter adjacent to the amide carbonyl group. This memory of chirality is suggested to occur by transfer of chirality from a stereocenter to an axis, then from the axis back to a new stereocenter.
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Lacôte E, Curran DP, Lalevée J. NHC-boranes: air- and water-tolerant co-initiators for type II photopolymerizations. Chimia (Aarau) 2012; 66:382-5. [PMID: 22871279 DOI: 10.2533/chimia.2012.382] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
N-Hetereocyclic carbene (NHC) complexes of boranes are stable compounds that can be used as co-initiators for the type II photopolymerization of acrylates. The present account summarizes this new development for polymerization and boron chemistry. In particular, NHC-boranes are air- and water-tolerant, which enhances the practicality of the photopolymerizations.
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78
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Taniguchi T, Curran DP. Silica Gel Promotes Reductions of Aldehydes and Ketones by N-Heterocyclic Carbene Boranes. Org Lett 2012; 14:4540-3. [DOI: 10.1021/ol302010f] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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79
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Prokofjevs A, Boussonnière A, Li L, Bonin H, Lacôte E, Curran DP, Vedejs E. Borenium ion catalyzed hydroboration of alkenes with N-heterocyclic carbene-boranes. J Am Chem Soc 2012; 134:12281-8. [PMID: 22713106 PMCID: PMC3405176 DOI: 10.1021/ja305061c] [Citation(s) in RCA: 114] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Treatment of alkenes such as 3-hexene, 3-octene, and 1-cyclohexyl-1-butene with the N-heterocyclic carbene (NHC)-derived borane 2 and catalytic HNTf(2) (Tf = trifluoromethanesulfonyl (CF(3)SO(2))) effects hydroboration at room temperature. With 3-hexene, surprisingly facile migration of the boron atom from C(3) of the hexyl group to C(2) was observed over a time scale of minutes to hours. Oxidative workup gave a mixture of alcohols containing 2-hexanol as the major product. A similar preference for the C(2) alcohol was observed after oxidative workup of the 3-octene and 1-cyclohexyl-1-butene hydroborations. NHC-borenium cations (or functional equivalents) are postulated as the species that accomplish the hydroborations, and the C(2) selective migrations are attributed to the four-center interconversion of borenium cations with cationic NHC-borane-olefin π-complexes.
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80
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Merling E, Lamm V, Geib SJ, Lacôte E, Curran DP. [3 + 2]-Dipolar Cycloaddition Reactions of an N-Heterocyclic Carbene Boryl Azide. Org Lett 2012; 14:2690-3. [DOI: 10.1021/ol300851m] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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81
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Lalevée J, Telitel S, Tehfe MA, Fouassier JP, Curran DP, Lacôte E. N-Heterocyclic Carbene Boranes Accelerate Type I Radical Photopolymerizations and Overcome Oxygen Inhibition. Angew Chem Int Ed Engl 2012; 51:5958-61. [DOI: 10.1002/anie.201200975] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2012] [Indexed: 11/12/2022]
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82
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Moretti JD, Wang X, Curran DP. Minimal fluorous tagging strategy that enables the synthesis of the complete stereoisomer library of SCH725674 macrolactones. J Am Chem Soc 2012; 134:7963-70. [PMID: 22515682 DOI: 10.1021/ja302260d] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Four mixtures of four fluorous-tagged quasiisomers have been synthesized, demixed, and detagged to make all 16 stereoisomers of the macrocyclic lactone natural product Sch725674. A new bare-minimum tagging pattern needs only two tags--one fluorous and one nonfluorous--to encode four isomers. The structure of Sch725674 is assigned as (5R,6S,8R,14R,E)-5,6,8-trihydroxy-14-pentyloxacyclotetradec-3-en-2-one. Various comparisons of spectra of 32 lactones (16 with tags, 16 without) and 16 ester precursors (8 with tags, 8 without) provide insights into when and why related compounds have the same or different spectra.
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83
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Pan X, Lacôte E, Lalevée J, Curran DP. Polarity reversal catalysis in radical reductions of halides by N-heterocyclic carbene boranes. J Am Chem Soc 2012; 134:5669-74. [PMID: 22394128 DOI: 10.1021/ja300416f] [Citation(s) in RCA: 176] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Otherwise sluggish or completely ineffective radical reductions of alkyl and aryl halides by N-heterocyclic carbene boranes (NHC-boranes) are catalyzed by thiols. Reductions and reductive cyclizations with readily available 1,3-dimethylimidazol-2-ylidene borane and a water-soluble triazole relative are catalyzed by thiophenol and tert-dodecanethiol [C(9)H(19)C(CH(3))(2)SH]. Rate constants for reaction of the phenylthiyl (PhS•) radical with two NHC-boranes have been measured to be ~10(8) M(-1) s(-1) by laser flash photolysis experiments. An analysis of the available evidence suggests the operation of polarity reversal catalysis.
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84
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Tehfe MA, Monot J, Malacria M, Fensterbank L, Fouassier JP, Curran DP, Lacôte E, Lalevée J. A Water-Compatible NHC-Borane: Photopolymerizations in Water and Rate Constants for Elementary Radical Reactions. ACS Macro Lett 2012; 1:92-95. [PMID: 35578461 DOI: 10.1021/mz200087g] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Rate constants for important elementary reactions of 2,4-dimethyl-1,2,4-triazol-3-ylidene borane (1) and its derived boryl radical have been measured in the presence and absence of water. Reactions including H-abstraction by tBuO•, and onward reactions of the derived radical with methyl acrylate (addition), iodopropane (halogen abstraction), and an iodonium salt (oxidation) are unaffected by the presence of a high concentration (1.5 M) of water. Extending these results, borane (1) has been found to be an efficient new co-initiator for the visible light photopolymerization of monomers in the presence of both air and water.
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85
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Curran DP, Boussonnière A, Geib SJ, Lacôte E. The Parent Borylene: Betwixt and Between. Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201107238] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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86
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Curran DP, Boussonnière A, Geib SJ, Lacôte E. The Parent Borylene: Betwixt and Between. Angew Chem Int Ed Engl 2012; 51:1602-5. [DOI: 10.1002/anie.201107238] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2011] [Indexed: 11/08/2022]
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87
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Solovyev A, Geib SJ, Lacôte E, Curran DP. Reactions of Boron-Substituted N-Heterocyclic Carbene Boranes with Triflic Acid. Isolation of a New Dihydroxyborenium Cation. Organometallics 2011. [DOI: 10.1021/om201260b] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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88
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Horn M, Mayr H, Lacôte E, Merling E, Deaner J, Wells S, McFadden T, Curran DP. N-Heterocyclic Carbene Boranes are Good Hydride Donors. Org Lett 2011; 14:82-5. [DOI: 10.1021/ol202836p] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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89
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Bajpai R, Curran DP. Synthesis and spectroscopic analysis of a stereoisomer library of the phytophthora mating hormone α1 and derived bis-Mosher esters. J Am Chem Soc 2011; 133:20435-43. [PMID: 22047536 DOI: 10.1021/ja2082679] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Fluorous mixture synthesis provided all eight diastereomers of the phytophthora hormone α1 with the R configuration at C11 as individual samples after demixing and detagging. The library of all possible bis-Mosher esters (16) was then made by esterification. Complete sets of (1)H, (13)C, and (for the Mosher esters) (19)F NMR spectra were recorded, assigned, and compared with each other and with published spectra. Not all of the spectra are unique, and the (1)H NMR spectra of the Mosher esters provided the most information. The previous assignment of the natural sample as an "all-R" stereoisomer mixed with its 3S-epimer was confirmed.
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90
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Curran DP, Solovyev A, Makhlouf Brahmi M, Fensterbank L, Malacria M, Lacôte E. Cover Picture: Synthesis and Reactions of N-Heterocyclic Carbene Boranes (Angew. Chem. Int. Ed. 44/2011). Angew Chem Int Ed Engl 2011. [DOI: 10.1002/anie.201105618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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91
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Solovyev A, Lacôte E, Curran DP. Ring Lithiation and Functionalization of Imidazol-2-ylidene-boranes. Org Lett 2011; 13:6042-5. [DOI: 10.1021/ol202516c] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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92
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Curran DP, Solovyev A, Makhlouf Brahmi M, Fensterbank L, Malacria M, Lacôte E. Titelbild: Komplexe von N-heterocyclischen Carbenen mit Boranen: Synthese und Reaktionen (Angew. Chem. 44/2011). Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201105618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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93
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Jiménez M, Zhu W, Vogt A, Day BW, Curran DP. Efficient syntheses of 25,26-dihydrodictyostatin and 25,26-dihydro-6-epi-dictyostatin, two potent new microtubule-stabilizing agents. Beilstein J Org Chem 2011; 7:1372-8. [PMID: 22043248 PMCID: PMC3201051 DOI: 10.3762/bjoc.7.161] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Accepted: 09/12/2011] [Indexed: 11/29/2022] Open
Abstract
The dictyostatins are powerful microtubule-stabilizing agents that have shown antiproliferative activity against a variety of human cancer cell lines. Two highly active analogs of dictyostatin, 25,26-dihydrodictyostatin and 25,26-dihydro-6-epi-dictyostatin, were prepared by a new streamlined total synthesis route. Three complete carbon fragments were prepared to achieve maximum convergency. These were coupled by a Horner–Wadsworth–Emmons reaction sequence and an esterification. A late stage Nozaki–Hiyama–Kishi reaction was then used to form the 22-membered macrolide. The stereoselectivity of this reaction depended on the configurations of the nearby stereocenter at C6.
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94
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Bruch A, Fröhlich R, Grimme S, Studer A, Curran DP. One Product, Two Pathways: Initially Divergent Radical Reactions Reconverge To Form a Single Product in High Yield. J Am Chem Soc 2011; 133:16270-6. [DOI: 10.1021/ja2070347] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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95
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Curran DP, Solovyev A, Makhlouf Brahmi M, Fensterbank L, Malacria M, Lacôte E. Synthesis and reactions of N-heterocyclic carbene boranes. Angew Chem Int Ed Engl 2011; 50:10294-317. [PMID: 21898724 DOI: 10.1002/anie.201102717] [Citation(s) in RCA: 355] [Impact Index Per Article: 27.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Indexed: 11/10/2022]
Abstract
Boranes are widely used Lewis acids and N-heterocyclic carbenes (NHCs) are popular Lewis bases, so it is remarkable how little was known about their derived complexes until recently. NHC-boranes are typically readily accessible and many are so stable that they can be treated like organic compounds rather than complexes. They do not exhibit "borane chemistry", but instead are proving to have a rich chemistry of their own as reactants, as reagents, as initiators, and as catalysts. They have significant potential for use in organic synthesis and in polymer chemistry. They can be used to easily make unusual complexes with a broad spectrum of functional groups not usually seen in organoboron chemistry. Many of their reactions occur through new classes of reactive intermediates including borenium cations, boryl radicals, and even boryl anions. This Review provides comprehensive coverage of the synthesis, characterization, and reactions of NHC-boranes.
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96
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Curran DP, Solovyev A, Makhlouf Brahmi M, Fensterbank L, Malacria M, Lacôte E. Komplexe von N-heterocyclischen Carbenen mit Boranen: Synthese und Reaktionen. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201102717] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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97
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Zhao Q, Curran DP, Malacria M, Fensterbank L, Goddard JP, Lacôte E. N-Heterocyclic Carbene-Catalyzed Hydrosilylation of Styryl and Propargylic Alcohols with Dihydrosilanes. Chemistry 2011; 17:9911-4. [PMID: 21796697 DOI: 10.1002/chem.201101822] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Indexed: 11/08/2022]
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98
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Zhang H, Curran DP. A short total synthesis of (±)-epimeloscine and (±)-meloscine enabled by a cascade radical annulation of a divinylcyclopropane. J Am Chem Soc 2011; 133:10376-8. [PMID: 21663316 DOI: 10.1021/ja2042854] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The first stereoselective synthesis of epimeloscine has been accomplished in 13 total steps with a longest linear sequence of 10 steps. The core of the synthesis takes only five steps, the key ones being acylation, stereoselective tandem radical cyclization of a divinylcyclopropane to make two rings, and group-selective ring-closing metathesis of the resulting divinylcyclopentane to make the last ring.
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99
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Walton JC, Brahmi MM, Monot J, Fensterbank L, Malacria M, Curran DP, Lacôte E. Electron Paramagnetic Resonance and Computational Studies of Radicals Derived from Boron-Substituted N-Heterocyclic Carbene Boranes. J Am Chem Soc 2011; 133:10312-21. [DOI: 10.1021/ja2038485] [Citation(s) in RCA: 97] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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100
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Clark AJ, Curran DP, Geden JV, James N, Wilson P. Bond rotation dynamics of enamides: the effect of the acyl group and potential for chirality transfer during 5-endo trig radical cyclizations. J Org Chem 2011; 76:4546-51. [PMID: 21506580 DOI: 10.1021/jo200343z] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Barriers to rotation of the N-alkenyl bond in a series of N-cycloalkenyl-N-benzyl acetamide derivatives have been measured in different solvents by variable-temperature NMR experiments. The barriers range from 9.7 to 14.2 kcal/mol, depending on substituents on the acetamide acyl group. Polar solvents such as chloroform and methanol increase the barrier to rotation compared to nonpolar solvents such as toluene. The barrier to rotation of "mimics" for acetamide-based radicals are estimated. The relative order of the values of k(rot) for different acyl groups parallels their reported Taft E(s) paramaters. For successful chirality transfer in 5-endo trig radical cyclization, it is evident that rotations would need to be significantly slower than those reported here.
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