A Highly Diastereoselective Aldol Reaction of Dicobalt Hexacarbonyl Propynal Complex and Uncomplexed Propynal: A Stereoselective Divergent Synthesis of (.+-.)-PS-5 and (.+-.)-6-epi-PS-5.

Abstract The aldol reaction of cobalt complexes propynal 1 with O-silyl ketene O,S-acetals 3 gave the syn-products exclusively, while the uncomplexed propynal 2 , the corresponding anti-compounds. A successful application of these stereoselective reactions to a synthesis of (±)-PS-5 and (±)-6-epi-PS-5 is described.