Abstract: Methyl propiolate undergoes Lewis acid catalyzed reactions with alkenes in high yield. Mono-and 1, 2-disubstituted alkenes give mainly cyclobutenes. 1, I-Disubstituted, trisubstituted, and tetrasubstitutecl alkenes give only ene adducts. Use of ethylaluminum dichloride as catalyst allows the isolation of pure products from acid-sensitive alkenes. Functionalized alkenes containing nonbasic functional groups are suitable substrates. ...