ORGN 258 |
| We have reported that trialkylboranes/triarylborane react with sulfonium ylides to generate new boranes which can be transformed into alcohols/amines in high yields and ee. However, the reactions with mixed boranes suffered from competing migration of different groups of the borane. Here we report on the progress we have achieved on the borane-ylide chemistry employing 9-BBN derivatives. 9-BBN derivatives were reacted with sulfonium benzylide, and after oxidative workup, afforded both side-chain and substituent migrating products. However, using 9-BBN-vinyl derivatives, vinyl migration was predominant. The allylic boranes 3 generated could undergo stereospecific [1,3] borotropic rearrangement to afford another allylic boranes 4 upon warming. Both allylic boranes 3 and 4 formed were captured by benzaldehyde to afford homoallylic alcohols in very high diastereoselectivities and enantioselectivities.
Scheme 1
In conclusion, this study provides for the first time an efficient method to synthesize enantiomerically enriched α-substituted allylic boranes. |
|
Asymmetric Reactions and Syntheses
8:00 AM-11:40 AM, Monday, 11 September 2006 Moscone Center -- Room 131, Oral
Division of Organic Chemistry |
