Robert M. Christie

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

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.

Studies of heterocyclic compounds. Part 24. Syntheses of 6aλ4-thia-1,2,6-triazapentalenes

6aλ4-Thia-1,2,6-triazapentalenes, a new class of four-electron three-centre bonded compound, have been synthesised by the reaction of 1-aryl-6,6aλ4-dithia-1,2-diazapentalenes in dimethylformamide with ethanolic methylamine; by S(6)-methylation of 1-aryl-6,6aλ4-dithia-1,2-diazapentalenes with methyl fluorosulphonate and treatment of the resulting 2-aryl-5-(2-methylthiovinyl)-1,2,3-thiadiazolium fluorosulphonates with methylamine; and by the coupling of 1,3,4,6-tetra-alkyl-6aλ4-thia-1,6-diazapentalenes with arenediazonium tetrafluoroborates and concomitant elimination of a methyliminomethyl group. 3,4-Dialkyl-6aλ4-thia-1,2,6-triazapentalenes react with benzenediazonium tetrafluoroborate to give 3,4-dialkyl-1,6-diphenyl-6aλ4-thia-1,2,5,6-tetra-azapentalenes.

Studies of heterocyclic compounds. Part XVI. Mechanism of electrophilic substitution of 6a-thiathiophthens and related compounds: nitrosation with rearrangement

Nitrosation of 6a-thiathiophthens and related compounds occurs with rearrangement. 6a-Thiathiophthens, 1-oxa-6,6a-dithiapentalenes, and 1,6a-dithia-6-azapentalenes rearrange into 1-oxa-6,6a-dithia-2-azapentalenes, and 1,6-dioxa-6a-thiapentalenes into 1,6-dioxa-6a-thia-2-azapentalenes. 6a-Thiathiophthens react with nitrous acid with difficulty unless activated by strongly electron-releasing substituents. 2-t-Butyl-6a-thiathiophthen reacted at position 4 to give 3-formyl-5-t-butyl-1-oxa-6,6a-dithia-2-azapentalene in low yield. 2-Methylthio-5-t-butyl-and 2-dimethylamino-5-t-butyl-6a-thiathiophthen reacted readily at position 3 to give the methyl 3-dithiocarboxylate and the 3-NN-dimethylthiocarboxamide of 5-t-butyl-1-oxa-6,6a-dithia-2-azapentalene, respectively, selective desulphurisation of which afforded the corresponding S-methyl thioester and NN-dimethylcarboxamide. 5-Phenyl-, 5-t-butyl-, and 2,5-dimethyl-1-oxa-6,6a-dithiapentalene reacted smoothly at position 3 to give the corresponding 3-formyl(acetyl)-1-oxa-6,6a-dithia-2-azapentalenes. 6-Methyl-2-phenyl- and 6-methyl-2-t-butyl-1,6a-dithia-6-azapentalene also gave 3-formyl-1-oxa-6,6a-dithia-2-azapentalenes by hydrolysis in situ of the intermediate 3-methyliminomethyl-1-oxa-6,6a-dithia-2-azapentalenes. 1-Oxa-6,6a-dithiapentalenes and 1,6a-dithia-6-azapentalenes in which the reactive position 3(4) is blocked, reacted at position 3(4) with elimination of the formyl or methyliminomethyl group to yield 1-oxa-6,6a-dithia-2-azapentalenes. Nitrosation of 1,6-dioxa-6a-thiapentalene with nitrosyl hexafluorophosphate gave 3-formyl-1,6-dioxa-6a-thia-2-azapentalene, the first reported derivative of the 1,6-dioxa-6a-thia-2-azapentalene system. A mechanism is proposed to account for the various features of the electrophilic substitution of 6a-thiathiophthens and related hypervalent heterocyclic systems. It is proposed that reaction proceeds by way of stable 6π-electron monocyclic cations, such as 1,2-dithiolium and 1,2-oxathiolium.

Studies of heterocyclic compounds. Part 21. Reactions of 1-aryl-6,6a-dithia-1,2-diazapentalenes with electrophiles

1-Aryl-6,6a-dithia-1,2-diazapentalenes react with electrophiles at position 3. Bromination of 1-phenyl-, 1-p-bromophenyl-, 1-phenyl-5-t-butyl-, and 1-p-bromophenyl-5-t-butyl-6,6a-dithia-1,2-diazapentalene gave the 3-bromo-derivatives as the major products. Vilsmeier formylation of 1-phenyl-, 1-phenyl-5-t-butyl,- and 1-p-nitrophenyl-5-t-butyl-6,6a-dithia-1,2-diazapentalene took place with difficulty to give the corresponding 6,6a-dithia-1,2-diazapentalene-3-carbaldehydes. Nitration of 1-phenyl- and 1-phenyl-5-t-butyl-6,6a-dithia-1,2-diazapentalene gave the 3-nitro-derivatives as the main products. 3-Nitro-1-p-nitrophenyl-5-t-butyl-6,6a-dithia-1,2-diazapentalene, a minor product from the nitration of 1-phenyl-5-t-butyl-6,6a-dithia-1,2-diazapentalene, was also synthesised by the coupling of 3-nitromethylene-5-t-butyl-3H-1,2-dithiole with p-nitrobenzenediazonium tetrafluoroborate. Nitration of 3,4-dimethyl-1-phenyl-6,6a-dithia-1,2-diazapentalene, in which the reactive position 3 is blocked, gave as the major product 4-methyl-3-(1-nitroethylidine)-3H-1,2-dithiole by nitro-dediazoniation at position 3, together with 3,4-dimethyl-1-p-nitrophenyl-6,6a-dithia-1,2-diazapentalene. Nitrosation of 1-phenyl- and 1-phenyl-5-t-butyl-6,6a-dithia-1,2-diazapentalene took place with rearrangement to give 3-phenylazo- and 3-phenylazo-5-t-butyl-1-oxa-6,6a-dithia-2-azapentalene, respectively, as the main products. Nitrosation of the blocked 3,4-dimethyl-1-phenyl-6,6a-dithia-1,2-diazapentalene gave mainly 3,4-dimethyl-1-oxa-6,6a-dithia-2-azapentalene by nitroso-dediazoniation, some 4-methyl-3-(1-nitroethylidene)-3H-1,2-dithiole by nitrodediazoniation, and a small amount of 3,4-dimethyl-1-p-nitrophenyl-6,6a-dithia-1,2-diazapentalene. Coupling of 1-aryl-5-t-butyl-6,6a-dithia-1,2-diazapentalenes with arenediazonium tetrafluoroborates took place in acetonitrile with exchange of the arylazo-units. These results are interpreted on the basis of a previously proposed mechanism of electrophilic substitution of 6a-thiathiophthens and related four-electron three-centre bonded structures.

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

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.

Studies of heterocyclic compounds. Part XIX. Synthesis of 6,6a-dithia- and 6,6a-diselena-1,2-diazapentalenes

1-Aryl-6,6a-dithia- and 1-aryl-6,6a-diselena-1,2-diazapentalenes, two new classes of hypervalent heterocyclic compound, have been synthesised by the reaction of 3-methyl(ene)-1,2-dithiolium and 3-methyl(ene)-1,2-diselenolium salts, respectively, with arenediazonium fluoroborates. 1-Aryl-5-t-butyl-6,6a-dithia-1,2-diazapentalenes obtained from 3-methyl-5-t-butyl-1,2-dithiolium perchlorate were accompanied by small amounts of their 3-arylazo-substitution products, which were subsequently produced in high yield by reaction of the 1-aryl-5-t-butyl-6,6a-dithia-1,2-diazapentalenes with the corresponding arenediazonium fluoroborates. The results of 1H n.m.r. spectral studies and of X-ray crystallographic studies by other workers are discussed in relation to structure.