2-Vinylcyclobutanones by Cycloaddition of Vinylketenes to Simple Olefins

Article abstract of DOI:10.1002/hlca.19830660744

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 stereoselective with respect to the olefin 3, but less so with respect to the ketene 2, so that - where possible - two stereoisomers of 4 resulted, namely A and B, whose configurations were determined from their 1H-NMR spectra, mechanistic considerations and, in one case, 4f, by chemical correlation with a previously known cycloadduct 8.