Organic heterocyclothiazenes. Part 11. Dithiatetrazocines and dithiadiazolium chlorides

A reinvestigation of the reaction of benzamidine with sulphur dichloride failed to increase the yield of 3,7-diphenyl-1,5,2,4,6,8-dithiatetrazocine (1) but uncovered a new product, 4-phenyl-1,2,3,5-dithiadiazolium chloride (4). This salt is the major product of reaction of tris(trimethylsilyl)benzamidine (3) with sulphur dichloride (60%) or of benzamidine with disulphur dichloride (54%), the latter providing a particularly convenient route to (4). Benzamidine also reacts with S4N4 to give dithiatetrazocine (1), but the best synthesis of (1) so far available involves treatment of benzamidine with a mixture of bis-(p-tolylsulphonyl)sulphurdi-imide (5) and diphthalimimido sulphide (6); other products of this reaction are the 1,2,4,6-thiatriazines (7) and (8). Benzamidoxime and sulphur dichloride also give dithiatetrazocine (1) and dithiadiazolium chloride (4). 2-Furylamidine and 2-thienylamidine give the analogous dithiatetrazocines (9) and (10), and dithiazolium chlorides (11) and (12). Treatment of a mixture of benzamidine and dimethylguanidine with sulphur dichloride gives the first unsymmetrical dithiatetrazocine (13). The u.v. spectra of the diaryldithiatetrazocines [(1), (9), (10)] are all very similar, and typically 'aromatic', indicating the same planar, delocalized heterocyclic ring structure, but are very different from those of the dimethylamino derivatives (2) and (13) which have folded structures. Thus one dimethylamino substituent is sufficient to buckle the planar dithiatetrazocine ring. Dithiatetrazocine (1) is unreactive (no reaction with MCPBA, N2O4, chloramine-T, Ph3P, or CH2N2) but is reduced to benzamidine with hydrazine and palladium, and is oxidised by ozone, followed by ring contraction to give the thiatriazine (8). Mechanisms are suggested for new key reactions.