Abstract: Arylcarbenes carrying alkoxyalkyl groups in the ortho position have been generated by flash pyrolysis and photolysis of appropriate tosylhydrazone sodium salts. In the gas phase and in aprotic solvents, interaction of the carbenes with the lone electron pairs of oxygen competes efficiently with insertion into CH bonds. Both five-and six- membered cyclic oxonium ylides have been generated. The ylides 23, 37, 61b, and 74 ...