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20.5.9.1.5.3 Variation 3: Metal-Mediated C—C Bond Formation

DOI: 10.1055/sos-SD-020-01027

Westbrook, J. A.; Schaus, S. E.Science of Synthesis, (2007201125.

There has been extensive use of transition metals to mediate CC bond formation during the incorporation of difluoromethyl groups into organic compounds. Alkyl 2,2-difluoro-2-haloacetates are the most common compounds used for delivery of the difluoromethylene moiety. Scheme 9 summarizes the numerous reaction modes in which metals have been employed to facilitate such additions. Copper(0) is most commonly used during the cross coupling of vinyl halides, e.g. 38[‌50‌] and 39,[‌51‌] to either 2-bromo-2,2-difluoroacetates or 2,2-difluoro-2-iodoacetates (Scheme 9). Reformatsky-type reactions are also prevalent in the literature. For example, the nickel(0)-catalyzed coupling between the styrylzirconocene species 40 and isopropyl 2-bromo-2,2-difluoroacetate gives the 2,2-difluoro-substituted ester 41 in 65% yield.[‌52‌] More nucleophilic zirconium and zinc species have been generated from ethyl 2-chloro-2,2-difluoroacetate and ethyl 2-bromo-2,2-difluoroacetate; such species add to benzaldehyde (42)[‌53‌] and alkynylaldehydes such as 43 (Scheme 9).[‌54‌]

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