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44.2.2.4.1 Method 1: Dehalogenation of 1,1-Dihalocyclopropanes through Carbenoid Intermediates

DOI: 10.1055/sos-SD-044-00163

Gandon, V.; Malacria, M.Science of Synthesis, (200844218.

It was found in the early 1960s that allenes 110 can be prepared by treating 1,1-dihalocyclopropanes (usually 1,1-dibromocyclopropanes) with alkali metals[‌146‌] or alkyllithium reagents.[‌147‌‌150‌] This procedure is now referred to as the DoeringMooreSkattebøl reaction. A review summarizes developments of this reaction.[‌151‌] The mechanism of this transformation is likely to proceed via metalhalogen exchange, which generates a cyclopropylidene carbenoid.[‌152‌,‌153‌] Alkylmetals that give satisfactory results include methyllithium, ethylmagnesium bromide, and isopropylmagnesium bromide. To avoid side reactions, low temperatures are usually required with methyllithium.[‌151‌] On the other hand, Grignard reagents can be used at room temperature in tetrahydrofuran (Scheme 66).[‌154‌] Of particular interest, β-silylallenes, even macrocyclic ones, are readily available by this strategy.[‌9‌,‌155‌] In specific cases however, the insipient carbenoid inserts preferably into a silicon-activated CH bond.[‌155‌]

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