REACTIONS OF OXIMES WITH THIANTHRENE CATION RADICAL IN NITRILE SOLVENTS - CYCLOADDITION TO FORM OXADIAZOLES AND DEOXYGENATION TO FORM NITRILES

Reactions of eight oximes, RCH═NOH (la, R = C6H5; lb, R = 4-CH3C6H4; 1c, R = 4-N02C6H4; Id, R = 4- CH3OC6H4; le, R = 2-CH3OC6H4; If, R = 1-naphthyl; lg, R = C5H11; lh, R = C4H9), with thianthrene cation radical perchlorate (Th•+C104-) in acetonitrile under argon were studied. The major product from the oxime in all cases, but of 1d, was the nitrile, RCN. The anticipated product of oxidative cycloaddition, namely, a 3-R-5-methyl-l,2,4-oxadiazole (2), was obtained in substantial yield (2d, 66%) only in the case of 1d. An isomeric 5- R-3-methyl-l,2,4-oxadiazole (3) was obtained from some reactions, that is, 3c alone from lc, and a mixture of 2a and 3a from la. Neither 2 nor 3 was obtained in measurable amounts from reactions of lg and lh. The aldehyde (RCHO) was obtained in small yields from each reaction. Thianthrene (Th) and thianthrene 5-oxide (ThO) were also major products. Studies with [180]-lb and [180]-ld showed that the oxygen atom in 2 came entirely and in ThO primarily from the oxime. Studies of workup with H2180 showed that the workup water was the source of the oxygen atom in RCHO and to a small extent in ThO. Explanations are given for the formation of 2 by a stepwise addition of RCH═NOH•+ (1•+) to solvent nitrile and of 3 by the reaction of solvent nitrile with an oxaziridine cation radical (7, obtained from 1•+). © 1990, American Chemical Society. All rights reserved.