Aldol condensations of chiral ethylketones: Control by chiral boron reagents.

✍ Scribed by Ian Paterson; M. Anne Lister

• Publisher: Elsevier Science
• Year: 1988
• Tongue: French
• Weight: 302 KB
• Volume: 29
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)80157-4

✦ Synopsis

The chiral reagents (+)-and (-)-Ipc)2BOTf, in the presence of Et3N, are used to control the aldol condensation reactions of chiral ethylketone 5 with prochiral aldehydes. The SS isomer, 6 or 8, or SA isomer, 7 or 9, is then formed in >99% ee and with up to 93% diastereoselectivity.

The use of chiral boron reagents,lv2 such as (+) and (-)-1,s to control the enautio-and diastereoselective aldol condensation reactions of ketones with aldehydes is a powerful and practical alternative to chiral auxiliary methodology.4 We recently describedtb a concise approach to polypropionate-type fragments based on sequential ethylketone aldol condensations, where the diallqdboron enolate of 2, obtained using nBu2BOTf or 9-BBNOTf, gave the SS (i.e. 1,2-~yn-2,4-~yn) isomer 3 with good selectivity. This high substrate stereoselectivity, 2 --f 3, could be further improved by using the appropriate chiral boron triflate la of matched chiral influence, i.e. (+)-1. However, in the mismatched case using the enantiomeric reagent (-)-1, while the stcrcoselcctivity towards SS could be decreased, it could