INTRAMOLECULAR ADDITION-REACTIONS OF FUNCTIONALIZED ARYLCARBENES TO ARENES

[2-(Arylmethyl)phenyl]carbenes with Ar = phenyl (16), 1-naphthyl (20), and 2-furyl (24) have been generated photolytically from appropriate diazo or tosylhydrazone precursors. Intramolecular addition to the arene prevailed in pentane solution, insertion into ortho C-H bonds of the arene being a minor process. On direct photolysis in methanol, intermolecular O-H insertion predominated over intramolecular addition to phenyl and 1-naphthyl groups (k(S) < k(OH)). The ratio of addition to O-H insertion was not affected by benzophenone sensitization in the case of Ar = Ph, but increased strongly in the case of Ar = 1-naphthyl. These data, implying k(T) > k(TS) for 20, constitute the first evidence for the addition of triplet arylcarbenes to arenes. Ar = 2-furyl was found to promote the intramolecular addition of both singlet 24 (k(S) congruently k(OH)) and triplet 24 (k(T) > k(TS)). The reactivity of arenes toward electrophiles (k(S)) and the stabilization of diradical intermediates (k(T)) is thought to account for the observed trends.