Studies of heterocyclic compounds. Part 23. Diazo-coupling–deformylation of 3,4-dialkyl-1-aryl-6-oxa-6aλ4-thia-1,2-diazapentalenes: synthesis of 3,4-dialkyl-1,6-diaryl-6aλ4-thia-1,2,5,6-tetra-azapentalenes

Abstract

Partial desulphurisation of 3,4-dialkyl-1-aryl-6,6aλ⁴-dithia-1,2-diazapentalenes with mercury(II) acetate affords 3,4-dialkyl-1-aryl-6-oxa-6aλ⁴-thia-1,2-diazapentalenes, which couple with arenediazonium tetrafluoroborates with accompanying deformylation to give 3,4-dialkyl-1,6-diaryl-6aλ⁴-thia-1,2,5,6-tetra-azapentalenes, a new class of four-electron three-centre bonded compound. Reversible exchange of diazo-groups takes place between 3,4-dialkyl-1,6-diaryl-6aλ⁴-thia-1,2,5,6-tetra-azapentalenes and arenediazonium tetrafluoroborates in solution. It is proposed that the formation and the exchange reactions of 3,4-dialkyl-1,6-diaryl-6aλ⁴-thia-1,2,5,6-tetra-azapentalenes proceed by way of 1,2,3-thiadiazolium intermediates.