Studies of heterocyclic compounds. Part XX. Substitution of 1-oxa-6,-6a-dithiapentalenes with arenediazonium fluoroborates: rearrangement into 6,6a-dithia-1,2-diazapentalenes

Abstract

1-Oxa-6,6a-dithiapentalenes unsubstituted at position 3 couple with arenediazonium fluoroborates with accompanying rearrangement. 1-Oxa-6,6a-dithiapentalene and its 5-t-butyl and 5-phenyl derivatives gave 1-aryl-3-formyl-6,6a-dithia-1,2-diazapentalenes and the corresponding 5-substituted analogues, respectively. 1-Oxa-6,6a-dithiapentalenes in which the reactive position 3 is blocked, couple with p-nitrobenzenediazonium fluoroborate with accompanying deformylation. 3,4-Dimethyl- and 3-methyl-5-phenyl-1-oxa-6,6a-dithiapentalene gave 3,4-dimethyl-1-p-nitrophenyl- and 3-methyl-1-p-nitrophenyl-5-phenyl-6,6a-dithia-1,2-diazapentalene, respectively, and 4,5-dihydro-3H-1-oxa-7,7a-dithiacyclopent[cd]indene gave 6,7-dihydro-2-p-nitrophenyl-5H-2a,3-dithia-1,2-diazacyclopent[cd]indene. 4,5,6,7-Tetrahydro-2-t-butyl-8-oxa-1,8a-dithia-cyclopent[a]indene reacted with p-nitrobenzenediazonium fluoroborate (i) in acetonitrile to give 5-(1-p-nitro-phenyl-5-t-butyl-6,6a-dithia-1,2-diazapentalen-3-yl)pentanoic acid, and (ii) in methanol to give methyl 5-(1–p-nitrophenyl-5-t-butyl-6,6a-dithia-1,2-diazapentalen-3-yl)pentanoate. These results are accounted for by a previously proposed mechanism of electrophillic substitution of 1-oxa-6,6a-dithiapentalenes and related heterocyclic systems.