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Please login to access the full content or check if you have access via Variation 1: Of Ketenes and Alkenes

DOI: 10.1055/sos-SD-026-00397

Salaün, J.Science of Synthesis, (200526565.

Although the most common nonphotolytic route to four-membered carbon rings is that of [2+2] cycloaddition of ketenes to alkenes, the parent ketene and simple alkylketenes are inert toward nonactivated or electron-deficient alkenes. Therefore, this method is limited to specific classes of alkenes, namely electron-rich and activated alkenes. Moreover, the reaction has the disadvantage of competing dimerization and oligomerization of the starting ketenes. Nevertheless, the [2+2] cycloadducts of arylketenes and cyclopentadiene can be obtained in good yields. For example, dehydrohalogenation of 2-phenylpropanoyl chloride by triethylamine gives 2-methyl-2-phenylketene, which reacts very smoothly with cyclopentadiene to give the endo-cycloadduct 37 in 85% yield as a single diastereomer (Scheme 15).[‌41‌]

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