Studies of heterocyclic compounds. Part XI. 1-Oxa-6,6a-dithia-2-azapentalenes, 1-oxa-6,6a-diselena-2-azapentalenes, and 3-nitromethylene-3H-1,2-dithioles

Nitrosation of 3-alkyl-1,2-dithiolium salts gives 1-oxa-6,6a-dithia-2-azapentalenes (3-nitrosomethylene-3H-1,2-dithioles) in excellent yield. 3-Alkyl-1,2-diselenolium salts likewise afford 1-oxa-6,6a-diselena-2-azapentalenes (3-nitrosomethylene-3H-1,2-diselenoles), a new class of heterocyclic compounds. Attempted nitration of 2-t-butyl-6a-thiathiophthen with tetranitromethane gave 3-formyl-5-t-butyl-1-oxa-6,6a-dithia-2-azapentalene and a small amount of 5-t-butyl-1-oxa-6,6a-dithia-2-azapentalene. 2-Phenyl-6a-thiathiophthen behaved analogously. 3,4-Dimethyl-6a-thiathiophthen and 4,5-dihydro-3H-benzo[cd][6a]thiathiophthen gave products of partial desulphurisation, nitration, and nitrosation in low yield. The significance of 1H n.m.r. spectral data is discussed in relation to structure of the reaction products.