On the mechanism of thermal ring expansion of 3,3-dialkyloxindoles

Abstract

13 C Labelling experiments show that the title reaction takes place by a free radical mechanism which involves (i) homolysis of the C(3)–alkyl bond, (ii) rearrangement of the resulting 3-indolyl radical to a 3-indolylmethyl radical [e.g., (7)], (iii) ring expansion by competitive neophyl rearrangement or attack at the carbonyl position, and (iv) aromatisation by loss of a hydrogen atom.