Ketenes heterodimerization

Coupled with these developments, and driven through astute reaction design, commercially available Lewis base catalysts have allowed the first general asymmetric ketene heterodimerization to be realized. This has allowed facile... 

The literature in the field of controlled ketene cross-dimerization is relatively sparse, with the lack of suitable catalysts to preferentially enable heterodimerization as opposed to homodimerization a recurring problem in establishing a useful synthetic protocol. Sporadic reports of controlled heterodimerization of unusual ketene classes exist in the literature, but are limited to halogenated [64] and cyano-ketenes [65]. Nevertheless, the laboratory of Romo was able to successfully dehydrohalogenate acid chlorides to generate racemic ketene heterodimers used as intermediates in the preparation of salinosporamide A and cinnabaramide A [42b]. 

The asymmetric 2 + 2-heterodimerization of ketenes has succeeded by the slow addition of the monosubstituted ketene donor to the disubstituted acceptor. ... 

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