Methyl 2, 3-butadienoate (1) undergoes EtAIClz-catalyzed stereospecific [2+ 21 cycloadditions with alkenes to give methyl cyclobutylideneacetates in good yield. The stereospecificity and ratios of E and 2 isomers suggest a [, 2,+, 2,] cycloaddition of the 1- EtA1Clz complex analogous to that of ketenes.
