Chiral synthesis via organoboranes. Part 32. Synthesis of B-(cycloalk-2-enyl)diisopinocampheylboranes of high enantiomeric purity via the asymmetric hydroboration of cycloalka-1,3-dienes. successful asymmetric allylborations of aldehydes with B-(cycloalk-2-enyl)diisopinocampheylboranes
- 1 January 1991
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 1
- No. 11,p. 2633-2638
- https://doi.org/10.1039/p19910002633
Abstract
The hydroboration of cycloalka-1,3-dienes (CnH2n–4, n= 6, 7 and 8) with diisopinocampheylborane, (dIpc2BH or IIpc2BH) at –25°C provides highly enantiomerically pure B-(cycloalk-2-enyl)diisopinocampheylboranes, I or dIpc2BCnH2n–3( 93% ee). Surprisingly, these allylic borane derivatives retain their stereochemical integrity at –25 °C although such compounds are capable of undergoing racemization through rapid allylic rearrangements. Furthermore, the B-(cycloalk-2-enyl)diisopino-campheylboranes achieve allylborations of aldehydes at –78 °C and afford 1 -(cycloalk-2-enyl)alkan-1- ols in 90–95% ee and 100%syn-diastereoselectivity.Keywords
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