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. 2011 Apr 20;133(15):5744-7.
doi: 10.1021/ja2010187. Epub 2011 Mar 30.

Enantioconvergent hydroboration of a racemic allene: enantioselective synthesis of (E)-δ-stannyl-anti-homoallylic alcohols via aldehyde crotylboration

Ming Chen  1 , William R Roush
Affiliations

Enantioconvergent hydroboration of a racemic allene: enantioselective synthesis of (E)-δ-stannyl-anti-homoallylic alcohols via aldehyde crotylboration

Ming Chen et al. J Am Chem Soc. .

Abstract

The enantioconvergent hydroboration of racemic allenylstannane (±)-1 with ((d)Ipc)(2)BH converts both enantiomers of (±)-1 into the enantioenriched crotylborane (S)-E-3. Subsequent crotylboration of aldehydes with (S)-E-3 provides (E)-stannyl-homoallylic alcohols 5 in good yields and with excellent enantioselectivity.

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Figures

Figure 1
Figure 1
Proposed enantioselective hydroboration of racemic allenylstannane (±)-1 and subsequent crotylboration reactions.
Figure 2
Figure 2
Proposed reaction pathway and hydroboration-allylboration of single enantiomeric allenes (P)-1 and (M)-1.
Figure 3
Figure 3
Proposed hydroboration pathways for the two enantiomers of allenylstannane (±)-1. The (R)- or (S)-descriptor defines the configuration of the allylic borane stereocenter in each intermediate, E and Z denote the double bond configuration, and the “d” superscript denotes the absolute configuration of the Ipc2B—unit. Thus, (S)d-E-3 and (R)d-E-3 are diastereomers and not enantiomers.
Figure 4
Figure 4
Hydroboration-allylboration of allenylstannane (P)-1 with Cy2 BH.
See this image and copyright information in PMC

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