Acylarylnitrosamines. Part II. The formation of arynes in the anomalous decompositions of o-t-butyl- and 2,5-di-t-butyl-N-nitrosoacetanilide

Abstract

Decomposition of o-t-butyl-N-nitrosoacetanilide in benzene gives o- and m-t-butylphenylacetates (55%) rather than the expected high yield of 2-t-butylbiphenyl. The isolation of aryne adducts in the presence of furan, anthracene, and 2,3,4,5-tetraphenylcyclopentadienone and the results of aryne-competition experiments involving anthracene and 9,10-dimethoxyanthracene, establish the participation of 3-t-butylbenzyne. 2,5-Di-t-butyl-N-nitrosoacetanilide similarly decomposes, in part, via 3,6-di-t-butylbenzyne. These abnormal decompositions are considered to arise as a result of preferential steric acceleration of unimolecular decomposition of the o-t-butylaryldiazonium cations to the corresponding carbonium ions, which either are converted into the ortho-acetates or to the aryne, which reacts with acetic acid to give m-acetate. These arynes, in turn, are considered to be less reactive as a result of steric hindrance.