2,1,3-Benzoselenadiazoles as Valuable Synthetic Intermediates

Abstract

N-alkyl-1,2-benzenediamines, 4-substituted-3-nitro-1,2-benzenediamines and 3,4-diamino-2-nitrophenols are readily obtained by deselenation of alkyl quaternary salts of 2,1,3-benzoselenadiazoles (bsd) and 5-substituted-4-nitro-bsd. The latter are easily obtained by nitration of 5-X-bsd (X = Me, Br, Cl, F, OMe, NHMe). Nitration of 5-fluoro-bsd yields the 4-nitro derivatives that are accompanied by substantial amounts of the corresponding 4-nitro-bsd-5-ols. ipso-Nitration of 5- fluoro-4-methyl-bsd is followed by instantaneous hydrolysis to (±)-4-methyl-4-nitro-bsd-5(4H)-one. Batcho-Leimgruber indole synthesis on 5-methyl-4-nitro-bsd followed by reductive deselenation of 1,2,5- selenadiazolo[3,4-g]indole affords 6,7-diaminoindole. Cyclocondensation of 3-nitro-1,2-benzenediamines with acetylacetone provides a convenient route for the preparation of 2-methyl-4-nitrobenzimidazoles. Less-accessible 6-halo-5-nitro- and 6-methoxy-5-nitroquinoxalines are efficiently synthesized by regioselective condensation of a-dicarbonyls with 4-halo- and 4-methoxy-3-nitro-1,2-benzenediamines. The reactive halogen atom or methoxyl group ortho to the nitro substituent renders these quinoxalines versatile intermediates to further heterocycles. The 77Se, 13C and 1H NMR chemical shifts of sixteen bsd derivatives, and the 13C NMR chemical shifts of eight derivatives of 2-methylquinoxalines are presented.