Stereocontrol in asymmetric phospho-aldol catalysis.Chirality relaying in action

摘要

The enantioselective addition of diorgano-H-phosphonates to aldehydes,the phospho-aldol reaction,is catalysed by both(R,R)-salcyen and(R,R)-salcyan complexes of aluminium at room temperature under aerobic conditions.However,whilst the former ligand System faveurs one absolute configuration of product alpha-hydroxyphosphonate ester,to the extent of <50%,the latter ligand framework faveurs the opposite configuration < 60%,despite both ligand Systems having the same absolute backbone configuration ! Structure-activity,single-crystal X-ray and computational studies shed light about these differences and provide important dues as to how to increase stereoselectivity.