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47.1.4.7.1 Variation 1: Dehalogenation of Geminal Dihalides

DOI: 10.1055/sos-SD-047-00322

Kostikov, R. R.; Khlebnikov, A. F.; Sokolov, V. V.Science of Synthesis, (201047840.

The reductive dehalogenation of geminal dihalides cannot really be considered as a versatile synthetic route to alkenes. In the literature there are only a few examples of such reactions having a preparative importance. The reduction of gem-dihalides may proceed via either radical or carbenoid intermediates. Thus, photolysis of a number of (dihalomethyl)cycloalkanes in various solvents leads to complex mixtures containing alkenes with both unchanged and rearranged skeletons.[‌253‌] The carbenoids formed from gem-dibromides 116 and butyllithiumdiethyl ether rearrange to alkenes 117 with acceptable yields (Scheme 46).[‌254‌] For simple alkenes, this reaction has a synthetic value only in the case of terminal gem-dibromides, whereas from internal gem-dibromides, mixtures of regio- and stereoisomers are formed. Terminal gem-dichlorides under the same conditions provide alkynyllithium compounds instead of alkenes. The reductive rearrangement of 2-alkyl-1,1-dibromocyclobutanes 118 upon treatment with methyllithium at 78°C affords the alkylidenecyclopropanes 119 in good yields (Scheme 47).[‌255‌]

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