Reactions of Oximes with Thianthrene Cation Radical in Nitrile Solvents. Cycloaddition To Form Oxadiazoles and Deoxygenation To Form Nitriles

Article abstract of DOI:10.1021/jo00297a045

Reactions of eight oximes, RCH=NOH (1a, R= C6H5; 1b, R= 4-CH3C6H4; 1c, R= 4-NO2C6H4; 1d, R= 4-CH3OC6H4; 1e, R= 2-CH3OC6H4; 1f, R= 1-naphthyl; 1g, R= C5H11; 1h, R= C4H9), with thianthrene cation radical perchlorate (Th^.+ClO4^-) 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-1,2,4-oxadiazole (2), was obtained in substantial yield (2d, 66percent) only in the case of 1d.An isomeric 5-R-3-methyl-1,2,4-oxadiazole (3) was obtained from some reactions, that is, 3c alone from 1c, and a mixture of 2a and 3a from 1a.Neither 2 nor 3 was obtained in measurable amounts from reactions of 1g and 1h.The aldehyde (RCHO) was obtained in small yields from each reaction.Thianthrene (Th) and thianthrene 5-oxide (ThO) were also major products.Studies with <18O>-1b and <18O>-1d showed that the oxgen atom in 2 came entirely and in ThO primarily from the oxime.Studies of workup with H2¹⁸O showed that the workup water was the source of the oxgen 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^.+).