Brönsted and Lewis acid catalysis of XY–ZH cycloadditions

Cycloadditions of arylidene imdines of methyl phenylglycinate show substantial rate enhancement in the presence of Brönsted and Lewis acids; for Brönsted acids the rate is related to the pKa of the acid, whilst for the Lewis acids studied the rate acceleration decreased in the order Zn(OAc)2 > AgOAc > LiOAc > Mg(OAc)2.