Investigation of the Reaction of 2-Bromo-1,4-dimethoxynaphthalene and 9-Bromophenanthrene with Nitriles Under Aryne-Forming Conditions

The reaction of 2-bromo-1,4-dimethoxynaphthalene (1) and 9-bromophenanthrene (3) with nitriles 2 under base-mediated, aryne-forming conditions gives product distributions which depend upon the nature of the bromoarene, nitrile, base, and the reaction medium. Thus, treatment of 1 with arylacetonitriles 2a-d in the presence of LDA in THF or sodium amide in liquid ammonia supplies α-aryl-1,4-dimethoxy-2-naphthylacetonitriles 4a-d, presumably by the aryne arylation mechanism. In contrast, the reaction of 9-bromo-phenanthrene (3) and arylacetonitriles 2b-e with LDA in THF yields 10-arylmethyl-9- phenanthrenecarbonitriles 6b-e, most likely by the tandem addition-rearrangement pathway. When 3 reacts with 2a-c in the presence of sodium amide and liquid ammonia, α-aryl-9-phenanthrylacetonitriles 5a-c, rather than the rearranged nitriles 6a-c, are obtained. Both 1 and 3 react with alkylnitriles 2f-i and LDA-THF, sodium amide-liquid ammonia, or Caubere's sodamide base to afford aryne arylated nitriles (4f-i and 5f-i, respectively). An explanation in terms of the influence of reactants and solvent on the competition between the aryne arylation and tandem addition-rearrangement pathways is presented.