Mechanism of ipso aromatic substitution by reaction of aryloxy(methoxy)carbenes and diaryloxycarbenes with DMAD

Abstract

Some aryloxy(methoxy)carbenes and diaryloxycarbenes attack dimethyl acetylenedicarboxylate (DMAD) with aryl group transfer to an alkyne carbon of DMAD. In this study diaryloxycarbenes with different aryl groups that could be transferred competitively, were generated in the presence of DMAD to probe for the mechanism of that ipso aromatic substitution. It was found that a para electron-withdrawing substituent, relative to an electron-donating substituent, facilitated migration of an aryl group. Mechanisms in accord with these findings involve initial nucleophilic attack by the carbene at an alkyne carbon of DMAD. That step is followed by either nucleophilic, ipso attack on the aromatic ring or by electron transfer, from the side chain of the aromatic ring into the ring itself.Key words: aromatic substitution, diaryloxycarbene, DMAD, ipso, nucleophilic.