REACTION OF HEXACHLOROBENZENE AND (PENTACHLOROPHENYL)LITHIUM WITH ALPHA-ARYLACETONITRILES

摘要

(Pentachlorophenyl)lithium (2) reacts with alpha-lithio-alpha-arylacetonitriles (4) at -70 degrees C to room temperature to supply alpha-aryl-alpha-(2,3,5,6-tetrachlorophenyl)ace a. Small amounts of 1,2,4,5-tetrachlorobenzene (8) and trans-1,2-dicyano-1,2-diarylethylenes 9 are also obtained; however, no alpha-tetrachloroarylated nitriles 6 from 3,4,5,6-tetrachlorobenzyne were detected. Similar treatment of hexachlorobenzene (1) and 4 afforded alpha-aryl-alpha-(2,3,4,5,6-pentachlorophenyl)acetonitriles 10. The addition of 2 to 4 at tetrachlorobenzyne-generating temperatures (0-20 degrees C) gave a complex mixture containing mainly dimeric and polymeric materials; 6 was not found. A mechanism is proposed for the reaction of 2 and 4 which suggests that nitriles 7 are formed by the condensation of 2 and 4 via a four-centered transition state and that alkenes 9 are supplied by a base-mediated dimerization of alpha-chloro-alpha-arylacetonitriles 13, formed by a lithium-chlorine exchange between 2 and 4. Nitriles 10 most likely are provided from the reaction of 1 and 4 by the usual aromatic nucleophilic substitution pathway. [References: 27]