Lewis acid-catalyzed Meyer-Schuster reactions: methodology for the olefination of aldehydes and ketones

In principle, the most efficient and atom-economical means of converting an aldehyde or ketone into the homologated alpha,beta-unsaturated ester is through addition/rearrangement sequences involving acetylenic pi-bonds (Scheme 1). Implementation of such a strategy for the synthesis of a,o-unsaturated esters is presented: addition of ethoxyacetylene followed by scandium(III) triflate-catalyzed Meyer-Schuster rearrangement reaction. Stereoselectivities range from good to excellent in the formation of disubstituted alpha,beta-unsaturated esters from aldehydes (Table 3). The two-stage olefination of even the most hindered ketones proceeds with near perfect efficiency (Table 4). (C) 2008 Elsevier Ltd. All rights reserved.