Unexpected Regioselectivity Switch: Organophosphine-Triggered Reactions of Cyclopropene-1,1-dicarboxylates with Aldehydes

With tris(4-methoxyphenyl)phosphine as the nucleophilic reagent, the readily available cyclopropene-1,1-dicarboxylates undergo a ring-opening reaction to generate a Wittig-type intermediate, which would react with aromatic aldehydes to yield (E)-5-aryl-2-(methoxycarbonyl)-2,4-pentadienoates. It is interesting to observe that the regioselectivity of the ring-opening reaction is switched.