Imino-l,2-dithiole

Treatment of a,/l-unsaturated hydrazones 100 with sulfur monochloride gave 3-imino-l,2-dithioles 101 in low yields (1985ZC400 Scheme 50). 

Two-component reactions, involving dilithiated ethyl thioglycolate and l,2-diimidoyl-l,2-dichloroethanes 250, gave rise, under the conditions specified in Scheme 40, to 4-imino-l,2-dithioles 251 in relatively modest yields (23-30%). Depending on the experimental conditions, instead of 251, 2,5/7-pyrrol-5-ones, 477-thiopyrans, and 6/7-1,3-oxazines can be prepared <1999CC2439, 2006JOC2332>. 

The hydrochlorides of 5-aryl-3-imino-l,2-dithioles (27 R = H, X = Cl) react with hydrazine to give known aminopyrazoles (28), and with benzoyl chloride and pyridine to give iV-benzoylimino-I,2-dithioles (29). The latter are sulphurized with phosphorus pentasulphide to yield 3-aza-6a-thiathiophthens. ... 

Syntheses and X-ray structures have been reported for (53) [94T11205] and (54) [95MI645], The preparation and non-linear optical properties of 2-imino-l,3-dithioles (55) have been described [95MI35] and the dimeric derivatives (R3 = p-phenylene) have also been reported [94BSF774]. The product (56), obtained from reaction of 4-methyl-5-phenyl-l,2-dithiol-3-thione with DMAD, undergoes cycloaddition with a further molecule of DMAD to afford the spiro compound (57) whose structure is confirmed by X-ray methods [94KGS908]. 

Amino- and imino-dithioles are available in some cases by ring syntheses, but the most general methods involve the reaction of an amine with a 3(or 5)-chloro-l,2-dithiolylium salt or. a chloro-l,2-dithiole respectively (80AHC(27)l5l), and protonation or alkylation of these gives aminodithiolylium salts. 

Aryl-3-JV-phenylimino-l,2-dithiol (78) condenses with a ketene to give 79 [Eq. (23)] which, when wanned, reverts to 78.98 Substituted ketenes with 78 give the corresponding 5-substituted 79. The related 5-phenylamino-3-imino-l,2,4-dithiazoline, when heated in acetic anhydride, rearranges to afford 2-acetylimino-3-phenyl-4-thiazolidinone (95%).99... 

It is easy to see that the true charge distribution in 1,3-dithiolium derivatives with typical electron-donating substituents in position 2 is most closely described by the iminium limiting formula (218) Addor accordingly referred to the compounds as hydrochlorides of the 2-imino-l,3-dithiole. The reader is referred back to the similar problem encountered in the cases of the 3,5-diamino-l,2-dithiolium... 

On the basis of this charge distribution, these compounds [cf. the discussion of the fused-ring analogs (Section III, A, 1, a) and of the 3,5-diamino-l,2-dithiolium salts (Table XI)] should be regarded as salts of 2-imino-l,3-dithiole rather than as 1,3-dithiolium salts. 

For the protonated species, various limiting forms may be considered, and their contributions to the resonance hybrid have been discussed in a previous review (Ref. 1 p. 54). The protonation equilibrium depends on the nature of X. When X is O, S, or Se, the protonated species exists in noticeable amounts only in strong acids such as concentrated sulfuric acid. On the other hand, when X is NR or CRR, the protonation is easy and the formation of the 3-imino- or 3-alkylidene-l,2-dithiole needs the action of a base. The protonation of 3-alkylidene-l,2-dithioles is discussed in the earlier review (Ref. 1 p. 57). 

Most 1,2-dithioles react with carbenes and nitrenes at the S—S bond, leading to insertion, and possible further loss of sulfur to form thiophenes or isothiazoles respectively (Scheme 9) <7474113, 76CJC3879). l,2-Dithiol-3-thiones (2b) usually react at the thione function, with the formation of thiiranes or thiaziranes respectively, which can extrude sulfur to form 3-methylene (2d) or 3-imino-... 

Under the same conditions 2-azido-2-methylsulfanyl-l,3-dithioles (69) afforded mixtures of 2-imino-l,3-dithiole (70) and the corresponding 1,4,2-dithiazines (71) (Scheme 15) <76JPRI27>. 

Imino-l,3-dithioles are easily converted into acylimines thus by treatment of (169) with phosgene or thiophosgene in the presence of pyridine the corresponding ureas (170) or thioureas (171) were obtained (Scheme 36) <76JPR127,79JPR827). 

New examples of thioacylation of active-methylene compounds with thiono- or dithio-esters have been reported. " Some new l,3-dithiol-2-ylidene-thioketones have been prepared by the cycloaddition reaction between acetylenes and l,2-dithiole-3-thiones. > The latter compounds and their imino-analogues yielded related cycloadducts (31) on treatment with ketens. The reaction of l,2-dithiole-3-thiones with a-chloro-benzylidenephenylhydrazine in basic medium gave the thioketones (32) by... 

C2oHi6N204,S2, 5-Benzamido-2-ben2oyl-imino-l, 3-dithiol 4-carbonic acid ethyl ester, 46B, 367... 

According to the original process of Addor (1962), phospholan is prepared by the reaction of ethylene-1,2-dithiol with cyanogen chloride, followed by the reaction of 2-imino-l,3-dithiolane (103) with diethyl phosphorochloridate. According to his later process (1970), N-(0,0-diethylphosphoryl) dithiocarbamate (104), obtained by the addition reaction of diethyl phosphoryl isothiocyanate and potassium hydrosulilde, is cyclised with ethylene bromide. 

The condensation of aldehydes with thiocyanoacetic esters, catalysed by potassium fluoride or potassium carbonate, gave as minor products yV-carbamoyl-2-imino-5-alkyl(or aryl)-l, 3-oxathiolan-4-carboxylic esters, in which the 4,5-c/j-isomers predominated according to n.m.r. spectroscopy. l,3-Oxathiolan-2-thione was converted into dimethyl 1,3-dithiol-2-one-4,5-dicarboxylate and ethylene on treatment with dimethyl acetylene-dicarboxylate, and the transformation of methyl 2-methoxycarbonyl-methyl-1,3-oxathiolan-2-carboxylate into dimethyl-5,6-dihydro-l, 4-oxa-thiin-2,3-dicarboxylate by chlorination at low temperatures found analogy in the reactions of 2,2-dialkyl-l,3-oxathiolans. Thiomethoxymethyl hexachloroantimonate reacted with potassium t-butoxide to give mainly 3,5,5-trimethyl-l,3-oxathiolanium hexachloroantimonate the mechanism of this remarkable reaction was not settled. ... 

---