Thermolysis of o-alkylnitrosobenzenes. Unusually ready [1,5] hydrogen shift involving a nitroso-group

Abstract

Thermolysis of 2,4-di-t-butyl-6-methylnitrosobenzene (1) in benzene afforded the corresponding aniline (2) and 5,7-di-t-butyl-2,1-benzisoxazole (3) in the ratio of 1 : 2; in methanol 2-t-butyl-4-methoxy-6-methylaniline (4) and 1-hydroxyimino-2,4-di-t-butyl-6-methoxy-6-methylcyclohexa-2,4-diene (5) were formed in addition to (2) and (3). In the presence of dimethyl actylenedicarboxylate, (1) gave (3) and N-(1,2-dimethoxycarbonylethylidene)-2,4-di-t-butyl-6-methylaniline N-oxide (7) in benzene. These facts together with the evidence of deuterium incorporation in product (3) and the recovery of (1) in the reaction in CH₃OD, allows us to postulate a reaction mechanism, the first step of which is formation of an o-quinone methide imine type intermediate via a [1,5] hydrogen migration from the benzylic position to the nitroso-oxygen. Thermolysis of 2,4-di-t-butyl-6-ethyl (or isopropyl)-, 2,4,6-trimethyl-, and 2-methylnitrosobenzenes were also found to proceed via a similar reaction mechanism.