Synthesis of 1-Substituted cis-Bicyclooctanones through Cycloadditions of Dichloroketene to Alkenes. Structural Characterization of Cycloadducts by Oxa-Ring Expansion

Article abstract of DOI:10.1021/jo00141a013

The <2 + 2> cycloaddition of dichloroketene to a series of 1-substituted cyclohexanes is shown to proceed in a highly regio- and stereospecific manner.The structures of the cycloadducts were determined by reductive dechlorination to the cyclobutanones, and the structures and stereochemistry of the latter as cis-bicyclo<4.2.0>octan-7-ones (4) were established by an oxa-ring expansion to the corresponding cis-octahydrobenzofuran-2-ones (6).The structures of the lactones 6 were established by 1H and 13C NMR studies which further indicated that these compounds exist in conformation 6a rather than 6b.The success of the regio- and stereospecific cycloaddition of dichloroketene to the 1-substitutd cyclohexenes discussed is found to be critically dependent on utilizing the zinc dehalogenation procedure for its in situ generation.Additional examples of the <2 + 2> cycloaddition of dichloroketene to indene, 1,4,-dihydronaphthalene and 1,2-dihydronaphthalene is also presented.