B,B-DIHALOTERPENYLBORANES AS REAGENTS FOR THE DIASTEREOSELECTIVE AND ENANTIOSELECTIVE SYNTHESIS OF SYN-ALDOLS

A series of known and new B,B-dihaloterpenylboranes, readily synthesiz ed from the corresponding terpenes, were examined for the diastereo- a nd enantioselective synthesis of syn-aldols. Thus, IpcBCl(2), EapBCl(2 ), LgfBCl(2), cis-MyrBCl(2), 2-IcrBCl(2), 4-IcrBCl(2), and 2-IcrBBr(2) in the presence of i-Pr2NEt, convert 3-pentanone to greater than or e qual to 99% Z-enolates, converted by aldehydes to pure syn-aldols in 7 -74% enantiomeric excess tee). The most efficient of these reagents, B ,B-dibromo-2-isocaranylborane, was tested for the enolboration of 3-pe ntanone, followed by aldolization with a series of aldehydes. (C) 1997 Elsevier Science Ltd.