Abstract Selected [2+ 2]-cycloadditions of three alkylvinylketenes 2 to one mono-and seven dialkyl-olefins 3 yielded eleven 2-alkyl-2-vinylcyclobutanones 4 (Tables 1 and 2). Three methods were compared, all involving in situ generation of the ketenes 2 by HCl-elimination from α, β-unsaturated acid chlorides 1; the most effective employed a large excess of olefin 3 and a high reaction temperature. The [2+ 2]-cycloadditions were fully regio-and ...