Preparation and Chemistry of α-Chloroalkyllithium Compounds. Their Role as Carbenoid Intermediates1
The reaction of polychloromethanes with n-butyllithium in tetrahydrofuran at low temperatures (–100°) via a-metalation or halogen-metal interconversion has been used to prepare a new class of organolithium reagents, the α-chloroalkyllithium compounds I-IV. The procedure was based on our observation of the remarkable stabilizing influence of tetrahydrofuran on α-chloroalkyllithium structures. At low temperatures, these compounds behave as typical organolithium structures and have been characterized by hydrolysis, deuterolysis, and direct carbonation to the corresponding acids (or derivatives). They react (couple) readily with the more reactive alkyl halides, presumably via nucleophilic displacements of the chloro carbanion on carbon. While these compounds were indefinitely stable at –100°, they decomposed spectacularly above –65°, suggestive of carbene formation via elimination of LiCl. If olefins were present during this decomposition (they were added without evidence of reaction at –100°), good yields of the corresponding cyclopropanes were obtained from α,α-dichlorobenzyllithium and trichloromethyllithium. In contraindication of a free carbene mechanism in the formation of the cyclopropanes, however, the stability of α-chloroalkyllithium compounds appears influenced by the more nucleophilic olefins, suggestive of a direct reaction of the olefin with the organolithium compound (or its structural equivalent), the reactivity (nucleophilic olefin sequence) and specificity in qualitative accord with results previously thought indicative of a free carbene intermediate. Several mechanisms are considered in the light of these results. © 1965, American Chemical Society. All rights reserved.
Hoeg, DF; Lusk, DI; Crumbliss, AL
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