Mechanism and Stereoselectivity of the Phosphinylation of 3-Acyl Coumarins-Stereocontrol Via Concurrent Aromatic Interaction/Oxaphosphole Formation

Racemic P-acetoxy-P-chloro phenylphosphonite reacts with prochiral 3-acylcoumarins yielding (2R,3R)/(2S,3S)-coumarino-3,4-c-2-oxo-2-phenyl-1,2-3H-oxaphospholes with >99% regio- and diastereoselectivity. The stereoselectivity is governed by the presence of phophonite phenyl group and oxaphosphole ring formation. The product has suitable conformation providing stereoselective route to (R,S)/(S,R) phosphino-substituted coumarins, normally inaccessible by the Phospha-Michael reaction employing achiral reagents.