Aldol reactions of methylketones using chiral boron reagents: A reversal in aldehyde enantioface selectivity

✍ Scribed by Ian Paterson; Jonathan M. Goodman

• Publisher: Elsevier Science
• Year: 1989
• Tongue: French
• Weight: 312 KB
• Volume: 30
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)95300-0

✦ Synopsis

The enantioselectivity of aldol additions of methyiketones to aldehydes using (-)-(Ipc)zBGTf, (-)-1, and P&NEt is generally lower (53-78% ee) than that for the corresponding ethylketone reaction and occurs with the opposite sense of aldehyde enantioface selectivity.

We recently reported a simple method for the enantioselective aldol addition of diethyhcetone to aldehydes to give syn-a-methyl-P-hydroxyketones,t which can also lead to useful stereocontrol in the aldol reactions of chiral ethylketones. In this method, the easily prepared chiral boron triflate reagents (-)-1 and (+)-1, in the presence of P&NEt or Et3N, give rise to both high levels of enolisation Z-stereoselectivity in the ketone 2 and x-face selectivity in the aldol (15) For two recent situations where such a method might prove useful, see: (a) Evans, D. A.;