Studies of heterocyclic compounds. Part 27. Routes to 1,6-dioxa-6aλ4-thia-2-azapentalenes, 1,6-dioxa-6aλ4-selena-2-azapentalenes, and 1-oxa-6aλ4-thia-2,5,6-triazapentalenes

Abstract

Partial desulphurisation of 3,4-dialkyl-1-oxa-6,6aλ⁴-dithia-2-azapentalenes with mercury (II) acetate gives 3,4-dialkyl-1,6-dioxa-6aλ⁴-thia-2-azapentalenes. 3,4-Dimethyl-1-oxa-6,6aλ⁴-diselena-2-azapentalene likewise gave 3,4-dimethyl-1,6-dioxa-6aλ⁴-selena-2-azapentalene. Peracid oxidation of 1-oxa-6,6aλ⁴-dithia-2-azapentalenes afforded 3-nitromethylene-3H-1,2-dithioles in low yield. 3,4-Dialkyl-6-oxa-6aλ⁴-thia-1,2-diazapentalenes in which the reactive position 3 is blocked, react with nitrous acid to give 3,4-dialkyl-1-oxa-6aλ⁴-thia-2,5,6-triazapentalenes by nitroso-deformylation, together with smaller amounts of the corresponding 5-nitromethylene-5H-1,2,3-thiadiazoles by nitro-deformylation. Peracid oxidation of 3,4-dialkyl-1-oxa-6aλ⁴-thia-2,5,6-triazapentalenes gave the corresponding 5-nitromethylene-5H-1,2,3-thiadiazoles in modest yield. 1,6-Dioxa-6aλ⁴-selena-2-azapentalenes and 1-oxa-6aλ⁴-thia-2,5,6-triazapentalenes are two new classes of four-electron, three-centre bonded compound.