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23.14.1 Product Subclass 1: Monoalkylketenes

DOI: 10.1055/sos-SD-023-00535

Tidwell, T. T.Science of Synthesis, (200623571.

Monoalkylketenes are typically generated by dehydrohalogenation of acyl chlorides,[‌24‌‌31‌] dehalogenation of α-haloacyl halides,[‌1‌,‌32‌,‌33‌] or Wolff rearrangements.[‌17‌,‌19‌] Butylketene can be obtained in solution for kinetic studies by photolysis of cyclohexanone.[‌34‌] All monoalkylketenes are prone to dimerization, and in the case of dehydrochlorination at elevated temperatures in solution, only the ketene dimers are isolated,[‌24‌‌28‌] although the ketenes can be trapped by means of cycloaddition reactions.[‌29‌‌31‌] Both methylene-β-lactone dimers and cyclobutane-1,3-dione dimers are known. The structures of the lactone dimer 11 and the enolized diketone dimer 12 from methylketene (1) were established in 1950 by Woodward and Small (Scheme 3).[‌35‌] The formation of lactone dimers is favored in dehydrochlorination reactions of acyl chlorides with triethylamine (Scheme 3),[‌24‌‌27‌] and it has been suggested that their formation is catalyzed by triethylamine hydrochloride, whereas the uncatalyzed reaction leads to cyclobutane-1,3-dione dimers.[‌36‌]

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