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Volumn 55, Issue 40, 2016, Pages 12285-12289

Stereospecific Synthesis of Alkenes by Eliminative Cross-Coupling of Enantioenriched sp3-Hybridized Carbenoids

Author keywords

alkenes; carbenoids; metalate rearrangements; organometallic reagents; stereoablation

Indexed keywords

ORGANOMETALLICS;

EID: 84990195235     PISSN: 14337851     EISSN: 15213773     Source Type: Journal    
DOI: 10.1002/anie.201606641     Document Type: Article
Times cited : (27)

References (48)
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    • Herein, “carbenoid” refers to any species containing a C atom bonded to both an electrofugal (M) and a nucleofugal (X) atom/group
    • Herein, “carbenoid” refers to any species containing a C atom bonded to both an electrofugal (M) and a nucleofugal (X) atom/group.
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    • Angew. Chem. 1967, 79, 15–27;
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    • for a discourse on the antecedent of StReCH, the stereoinductive substrate-controlled Matteson homologation, see
    • P. R. Blakemore, M. S. Burge, J. Am. Chem. Soc. 2007, 129, 3068–3069; for a discourse on the antecedent of StReCH, the stereoinductive substrate-controlled Matteson homologation, see:
    • (2007) J. Am. Chem. Soc. , vol.129 , pp. 3068-3069
    • Blakemore, P.R.1    Burge, M.S.2
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    • Lithiated carbamates were generated essentially as previously described by Aggarwal et al. (Ref. [15a]), beginning with catalytic enantioselective reduction of prochiral ketones using Noyori transfer hydrogenation. α-Carbamoyloxy boronates were made by (−)-sparteine/, s, -BuLi mediated lithiation–borylation of the appropriate, O, -alkyl, N, N, -diisopropyl carbamates according to the method of Hoppe et al.; see
    • Lithiated carbamates were generated essentially as previously described by Aggarwal et al. (Ref. [15a]), beginning with catalytic enantioselective reduction of prochiral ketones using Noyori transfer hydrogenation. α-Carbamoyloxy boronates were made by (−)-sparteine/s-BuLi mediated lithiation–borylation of the appropriate O-alkyl N,N-diisopropyl carbamates according to the method of Hoppe et al.; see: E. Beckmann, V. Desai, D. Hoppe, Synlett 2004, 2275–2280.
    • (2004) Synlett , pp. 2275-2280
    • Beckmann, E.1    Desai, V.2    Hoppe, D.3
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    • In this case, the putative ate complex, lk, -12 p rearranged with selective loss of the benzylic OCb nucleofuge; however, it should be noted that such regioselectivity is not generally required for successful eliminative cross-coupling because both possible regioisomers would converge to the same alkene. The relative stereochemistry of, lk, -13 n produced in an analogous manner was proven by oxidative deborylation (NaOOH) followed by cyclization (NaH, DMF, 100 °C) to give the corresponding epoxide, which was analyzed by, H NMR spectroscopy (NOESY). See the Supporting Information for details
    • 1H NMR spectroscopy (NOESY). See the Supporting Information for details.
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    • 85099675485 scopus 로고    scopus 로고
    • Given that both carbenoids in this case had 661 e.r. (97 %, ee,) the anticipated stereoselectivity for alkene formation would be, E, Z, =(66, +1)/(66+66)≈331 (i.e., 973). See Scheme 1 for the general formula
    • 2+1)/(66+66)≈33:1 (i.e., 97:3). See Scheme 1 for the general formula.
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    • X-ray diffraction analysis of (S)-10 n confirmed its gross structure and absolute stereochemistry. This α-carbamoyloxy boronate was observed to exist (in the solid state) in cyclic form with the carbonyl group O atom coordinated to a quaternized B atom. CCDC 1491635 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre
    • X-ray diffraction analysis of (S)-10 n confirmed its gross structure and absolute stereochemistry. This α-carbamoyloxy boronate was observed to exist (in the solid state) in cyclic form with the carbonyl group O atom coordinated to a quaternized B atom. CCDC 1491635 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre.
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    • syn, Elimination from, ul, -13 n is more rapid than from its epimer, lk, -13 n because for the latter, the two largest substituents (Ph and BnCH,) eclipse one another in the necessary reactive conformation. Facile spontaneous, syn, elimination from adducts such as, ul, -13 n (leading to, E, alkenes) means that, Z, alkenes should not be targeted from neopentylglycol boronates using, unlike, pairings and, anti, elimination
    • 2) eclipse one another in the necessary reactive conformation. Facile spontaneous syn elimination from adducts such as ul-13 n (leading to E alkenes) means that Z alkenes should not be targeted from neopentylglycol boronates using unlike pairings and anti elimination.
  • 46
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    • Eliminative dimerization of the lithiated carbamate was not a significant side reaction except for the α-lithioindanyl carbamate leading to alkene 20 (see the Supporting Information). The root cause of low yields is as yet unclearwe speculate that occurrences of poor stereoselectivity are due to competition between syn and anti elimination pathways
    • Eliminative dimerization of the lithiated carbamate was not a significant side reaction except for the α-lithioindanyl carbamate leading to alkene 20 (see the Supporting Information). The root cause of low yields is as yet unclear, and we speculate that occurrences of poor stereoselectivity are due to competition between syn and anti elimination pathways.


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