Reactivity of functionalized arylcarbenes. 2-Phenylethyl side chains and hetero analogues

Article abstract of DOI:10.1016/S0040-4020(97)00338-4

Phenylcarbenes with -X-CH₂Ph and -CH₂-X-Ph (X = CH₂, O, SiMe₂) groups in the ortho position were generated thermally and photolytically from diazo or tosylhydrazone precursors. Stereorandom insertion reactions with β-C-H bonds were observed, pointing to a triplet abstraction-recombination mechanism. Large kinetic and stereochemical deuterium isotope effects support this notion. The ample formation of benzocyclobutenes from 2-CH₂-X-Ph substrates is due to insertion of the carbenes into ArCH₂-X bonds. Addition to the terminal phenyl groups competes with C-H and C-X insertion. The results of benzophenone sensitization and of trapping with methanol suggest that the intramolecular reactions of functionalized arylcarbenes proceed, at best, competitively with spin inversion.