Nitrones and oxazirans. I. Preparation of 1 -pyrroline 1-oxides and 1-pyrrolines by reductive cyclization of γ-nitro carbonyl compounds

Abstract

A series of new pyrroline I-oxides and their related pyrrolines is described. Preparation of these compounds by reductive cyclization of y-nitro carbonyl compounds is discussed. This method is critically dependent on the reducing agent in the preparation of pyrroline 1-oxides and various procedures are assessed. Zinc in aqueous ammonium chloride is successful only in the formation of 2-aryl-5,5-dimethyl-substituted pyrroline 1-oxides and reduced iron in a mildly acidic medium is the method of choice for the corresponding 2-alkyl-substituted compounds. Pyrrolines were prepared either by deoxygenation of pyrroline 1-oxides or reductive cyclization of suitable γ-nitro carbonyl derivatives. Details of the N.M.R. spectra of these compounds are discussed.