N,O-heterocycles. Part 18. Regiochemistry and site selectivity of N-alkylhydroxylamine addition to 2,3-diphenylcyclopropenone

Abstract

This paper evaluates the reactivity of 2,3-diphenylcyclopropenone [CPO, (1)] towards N-alkylhydroxylamines and 2,2-dimethylnitrosoethane (4). CPO preferentially affords 2-methyl-4,5-diphenylisoxazol-3(2H)-one when it is treated with N-methylhydroxylamine, while treatment with higher homologues gives rise to acyclic products. 3,4-Diphenyl-2-t-butylisoxazol-5(2H)-one is formed when substrate (1) reacts with (4). The formation of the products is strongly affected by the oxidizing power of the α-nucleophiles which drive the population of the observed reaction channels from the 1,2 or 1,4 adducts initially formed. A general mechanism is proposed whereby isoxazolones are formed from CPO and both nitroso compounds and hydroxylamine.