New methodology is described for the enantioselective conversion of aldehydes to anti aldols 4 and homoallylic alcohols 7.
Previous studies in our laboratory have resulted in new methodology for enantioselective aldolization and allylation of aldehydes using recoverable reagents derived from (R,R)-or (S,S)-1,2-diamino-1,2-diphenylethane.1
The aldol reaction between aldehydes and achhal propionate esters (particularly the phenylthio ester) could be controlled to produce syn aldols with excellent diastereo-and enantioselectivity, but no conditions were found for the efficient production of the diastereomeric anti aldols. This fact and the lack of highly efficient, direct anti aldolization procedures, despite much research in this area,2 have encouraged us to search for new processes for enantioselective anti aldolization. Described herein is such a method. It is based on the use of the a-stannylated ester 1 and the boron reagent 2 to generate stereoselectively the boron enolate 3 which reacts with aldehydes to form anti aldols (4) (Scheme I). In addition we describe herein the application of the chiral boron reagent 2 to the enantioselective allylation and Zchloroallylation of aldehydes. The boron reagent 2 was produced from the (RR)-bissulfonamide 53 by reaction with BBQ in dry CH2C12.4 Reaction of 2 in 1: 2 toluene-hexane at -78'C with 1 for 5 h generated boron enolate 3. which upon Scheme I.