No abstract

4-Trithiadiazepine(1) and its benzo derivative (2) have planar delocalised lox and 14n aromatic structures, respectively; in the dihydro compound (3) the five heteroatoms are co-planar, with the approximately cis and trans periplanar methylene protons rapidly interconverting.An X-ray analysis of dimethyl 1,3,5,2,4-trithiadiazepine-6,7dicarboxylate revealed a planar geometry for the heterocyclic ring.1 The parent trithiadiazepine (1) and its benzo (2) and dihydro (3) derivatives have been synthesised2 and their X-ray crystallographic structures are now reported? together with the results of ab initio3a and MND03b calculations and the photoelectron spectra of ( 1) and (2).Trithiadiazepines ( 1) and (2) (Figures 1 and 2) both have the

The chemical, like the physical, properties of 1,3,5,2,4-trithiadiazepines broadly support their 1 On: aromatic nature. The parent compound (1 ) is thermally stable, though photochemically labile, does not undergo cycloaddition reactions characteristic of sulphur di-imides, is inert towards acids, amines, iodomethane, catalytic hydrogenation, and reacts only slowly with m-chloroperbenzoic acid. It undergoes electrophilic aromatic substitution smoothly to give mono-and di-nitro and mono-and di-bromo derivatives, though it could not be acylated. It is, however, sensitive to hydroxide and

Methyl trithiatriazepine-7-carboxylate (1 ), obtained from tetrasulphur tetranitride and dimethyl acetylenedicarboxylate, is hydrolysed t o the carboxylic acid (3) which is decarboxylated in boiling dioxane to give the parent 1 ,3h462,5,2,4,6-trithiatriazepine (4). Trithiatriazepine (4) is a remarkably stable 1 OK aromatic system similar to, although less polar than, the trithiadiazepine(2b). The triazepine ( 4) is less reactive towards electrophilic substitution than the diazepine (2b) but it can be nitrated with nitronium tetrafluoroborate, and brominated with N-bromosuccinimide in acetonitrile at 110 "C. The thermal stability of compounds (2b) and ( 4) suggests that the unknown sulphur nitride trithiatetrazepine (8) would be thermodynamically stable.In Part 1 of this series we reported that two minor products of the reaction of tetrasulphur tetranitride, S4N4, with dimethyl acetylenedicarboxylate (DMAD) in boiling toluene were methyl 1,3,5,2,4,6-trithiatriazepine-7-carboxylate (1) and dimethyl 1,3,5,2,4-trithiadiazepine-6,7-dicarboxylate (2a).2 Subsequently the parent trithiadiazepine (2b) was synthesized independently and shown to undergo ready electrophilic substitution in agreement with the proposed lox aromatic s t r ~c t u r e . ~ ( 2 ) a; R = C02Me b ; R = H

1 ,3h46',5,2,4-Trithiadiazepine (1 0) has been prepared from 1 -chloroethane-l,2-bis(sulpheny1 chloride)(1 1 ) and bis(trimethylsilyl)sulphurdi-imide (3) and also by dehydrogenation of the 6,7-dihydro derivative (9). Trithiadiazepine (10) is a planar, delocalised, stable 1 Ox aromatic system. Its benzo derivative (4), an analogous 1471 aromatic system, has been prepared from benzene-1 ,2-bis(sulpheny1 chloride) (2) and sulphurdi-imide (3). In 6,7-dihydro-1 ,3h46',5,2,4-trithiadiazepine (9), similarly prepared from ethane-l,2-bis(sulphenyl chloride) (8) and sulphurdi-imide (3), the five heteroatoms are accurately co-planar, with the out of plane methylene protons rapidly interconverting at room temperature. Reaction of S4N, with di-t-butyl acetylenedicarboxylate in boiling toluene gave di-t-butyl 1 ,3h462,5,2,4-trithiadiazepine-6,7-dicarboxylate (14) and t-butyl 1,3h46*,5,2,4,6-trithiatriazepine-7carboxylate (1 5) in low yield.