Loss of CO2 from the ortho isomer of deprotonated methyl phenyl carbonate involves a methyl migration

Abstract

The collision induced decompositions of the ortho-, meta, and para- (M-H)- anions of methyl phenyl carbonate were studied to see whether there is loss of CO2 occurring by the benzyne cine-substitution {(C6H4)--OCO2Me→ [(C6H4)MeOCO2-]→ (C6H4)--OMe+CO2}. Loss of CO2 is observed from the ortho isomer, but the process does not involve a benzyne cine substitution. It is a methyl migration through a six-centre transition state to give a cresol (M-H)- ion, probably ortho-MeC6H4-O-. Theoretical calculations [at the B3LYP/6-311++G(d,p)//HF/3-21+G(d) level of theory] indicate the methyl migration is a stepwise process, with the barrier for the first (and rate determining) step being 191 kJ mol-1. The overall process is calculated to be exothermic by 276 kJ mol-1. © 2001 Elsevier Science B.V.