A

Abstract

-alkyl allenoate esters aromatic aldehydes to give 4 H -1,3-di-oxin-6-yl-propanoates 14 with excellent diastereoselectivity. Mech- anistic studies revealed that these complex heterocycles are obtained as a result of a four-step reaction cascade consisting of two consec-utive Morita–Baylis–Hillman reactions on the α - and γ -position, an acetalization, and a final ring-closing intramolecular oxa-Michael reaction.