Cycloaddition/Ring-Opening Cascade Reaction of Alkylidene Azlactones for the Synthesis of α,α-Disubstituted α-Amino Acid Esters

Abstract

A metal-free, one-pot cascade reaction between alkylidene azlactones and N-phenacylbenzothiazolium salts, enabling efficient access to pyrrolo[2,1-b]benzothiazole-based amino acid esters. This solvent-controlled [3+2] annulation and methanol-triggered azlactone ring-opening constructs two C–C bonds and four contiguous stereogenic centers, including a quaternary carbon with excellent diastereoselectivity. The protocol offers high yields, broad substrate scope, and the mechanism is fully supported by spectroscopic and control studies.