Imino-l,2,3-dithiazole

Aminotetrazole reacts with 4,5-dichloro-l,2,3-dithiazolium chloride 166 to afford the bis(imino-l,2,3-dithiazole) 167 (20%) which in warm DMSO or DMF converts into the 1,2,3-clithiazolimine 168 (25%) (Scheme 16) <2002J(P1)1535>. 

In the condensations of o-aminohenzyl alcohol 376 or anthranilic acid 401 with 4,5-dichloro-l,2,3-dithiazolium chloride (Appel s salt) 402, imino-l,2,3-dithiazoles 403 were formed. Heating of the imino alcohol 403 (X = H2) in THE in the presence of NaH afforded an 11 1 mixture of 3,1-benzoxazine 404 and 3,1-benzothiazine 405 in moderate yield. Thermal cyclization of imino acid 403 (X = 0) resulted nearly quantitatively in formation of 3,1-henzoxazin-4-one 406 (Scheme 76) <1995CC1419, 1995J(P 1)2097, 1997SL704>. 

Following a similar strategy, Besson s group has also described the microwave-assisted thermocycHsation of imino-l,2,3-dithiazoles into imidazo[4,5,l-i/ ]quinolines (Scheme 3.50)80. 

In this section, the majority of new reactions are devoted to a continuation of the Appel salt chemistry, and its keto, thio, and ylidene derivatives, but imino-l,2,3-dithiazoles have attracted special attention by the Rees group. 

N-monosubstituted 1,2-diaminobenzenes react with Appel salt 20 in dichloromethane to give the corresponding 2-cyanobenzimidazoles 87 either directly or through thermal or acid-catalyzed rearrangement of the intermediate imino-l,2,3-dithiazoles 88, which can be isolated (Scheme 9). The reaction mechanism includes reversible attack of the o-amino group on the dithiazole ring <1998T9639>. 

When strongly heated, diaryl-5-imino-l,2,4-dithiazole-3-one (34 X = O, R = R = 4-MeOC6H4) loses COS to give a benzothiazole derivative (89) (91JPR579>. 3-Imino-l,2,4-oxathiazilidine-3-one (90) decomposes in solution at room temperature to give a carbodiimide (91) (Equation (6)) <86CB3737>. 

Amino-l,2,3,4-thiatriazole (207) when acylated with 0-aryl chlorothioformate (208) transforms into an unstable 5-aryloxy-3-imino-l,2,4-dithiazole hydrochloride (209). Acylation of this compound produces 2,5-bis(aryloxy)-l,6,6aA -trithia-3,4-diazapentalene ([210), which may be obtained more conveniently by acylating (207) with two equivalents of (208) (Scheme 44) <89M( 120)997, 90JPR208>. 

Amino- or -imino-l,2,4-dithiazole derivatives undergo a Dimroth rearrangement to... 

Scheme 24 Alkylation of 3-amino-5-imino-l,2,4-dithiazoles with 3-bromopropene...

In the alkylation of 5-dialkylamino-3-imino-l,2,4-dithiazoles (98), the occasional use of acetonitrile as solvent resulted in its 1,3-dipolar addition to the heterocycle, yielding 1,2,4-thiadiazoles (99) as the minor products.93... 

Thiadiazoles have been isolated as minor by-products in certain reactions of 5-(dialkylamino)-3-imino-l,2,4-dithiazoles in aceto- or benzo-nitrile as a result of 1,3-dipolar addition of the solvent. 

The 6//-l,3-thiazin-6-iminium hydroperchlorate salts 78-81 give interesting products when treated with nucleophiles <2003H(60)2273>. Hydrolysis of 6-imino-6//-l,3-thiazine hydroperchlorate 78 affords (2Z,4Z)-2-cyano-5-hydroxy-5-phenyM-azapenta-2,4-dienethioamide 82 in excellent yield, while treatment with morpholine gives 2-(morpholinomethylene)malononitrile 83 and thiobenzamide. The 5-(ethoxycarbonyl) -(methylthio)-2-aryl-6/7-l,3-thiazin-6-iminium salts 79 and 80 react with hydroxide or morpholine to afford ethyl 4-(methylthio)-2-aryl-6-thioxo-l,6-dihydropyrimidine-5-carboxylates 84 and 85. In the case of the 4-chloro analogue 80, the (Z)-ethyl 2-(5-(4-chlorophenyl)-37/-l,2,4-dithiazol-3-ylidene)-2-cyanoacetate 87 is also formed for the reaction with sodium hydroxide. The 1,2,4-dithiazoles 86 and 87 can be obtained as the sole product when 79 and 80 are treated with sodium acetate in DMSO. Benzoxazine 88 is isolated when the iminium salt 81 is treated with morpholine or triethylamine. Nitrile 89 is formed as a ( /Z)-mixture when 6-imino-67/-l,3-thiazine hydroperchlorate 79 is reacted with triethylamine and iodomethane in methanol <2003H(60)2273>. 

In a series of papers, Fromm and co-workers,12,64,188,189 beginning in 1893, showed that dithiobiurets could be oxidized with agents such as ferric chloride or halogens to salts of 3,5-diimino-l,2,4-dithiazolines (80) or 3-amino-5-imino-5/f-l,2,4-dithiazoles (81). These heterocycles were named thiurets by Fromm, and that term has persisted in the later... 

The interconvertibility of 1,2,4-dithiazoles and 1,2,4-thiadiazoles has been known for a long time. Examples of such reactions have been encountered in the study of isoperthiocyanic acid (3-imino-l,2,4-dithiazolidine-5-thione) and its analogs (the thiurets , isothiocyanate oxides and sulfides ), and their elucidation has not been as easy matter.1,3 The interpretation of these, and of novel conversions of 1,2,4-dithiazoles to 1,2,4-thiadiazoles has more recently been greatly aided by the application of physical methods, including X-ray analyses. Since the reactions are not all of one kind, it has been expedient to describe them in two separate Sections, among the syntheses of type A and type C, respectively. 

An equilibrium exists between the two forms of 2,3-dihydro [2,l-6][l,2,4]thiadiazole-3-thione (75) and 3-imino-3/7-imidazo[2,l-c][l,2,4]dithiazole (76) In the solid state the 2-substituent determines the preferred form, JV-alkyl existing in the former, iV-aryl in the latter form. In solution (76) is predominant (Equation (3)) <88JPC338>. 

Isothiocyanates react with 2-cyclohexyl 2,3-dihydro-imidazo[l,2-with exchange of the isocyanate moiety to give 2,3-dihydro-imidazo[l, 2-d][, 2,4]thiadiazole-3-thione derivative (75) or the isomer 3-imino-3//-imidazo[2,l-c][l,2,4]dithiazole (76), depending on the nature of the group R (see Section 8.05.4.3) (Scheme 37) <88JPC338>. 

Amino-3Yi 1,2,4 dithiazole-3-thione, 9CI. Isoperthiocyanic acid. 3-Imino l,2,4-dithiazolidine-5-thione. Xanthan hydride [6846-35-1]... 

In 1821 Wohler discovered that a solid deposited from concentrated aqueous solutions of thiocyanic acid. The solid, which was called isoperthiocyanic acid (3-imino-5-mercapto-1,2,4-dithiazole) (361), formed a new product perthiocyanic acid (3,5-dimercapto-l,2,4-thiadiazole) (18) when treated with alkali and then acid. On storage perthiocyanic acid (18) readily reverted to isoperthiocyanic acid (361) (65AHC(5)119). The mechanisms of these interconversions are still not known with certainty but the transformations outlined in Scheme 130 are suggested. Wohler proposed the initial formation of a dimer of thiocyanic acid for which structure (359) appears resonable. Addition of the imine function of (359) to the nitrile function of HSCN would produce the trimer (360) which could readily eliminate hydrogen cyanide to produce isoperthiocyanic acid (361). 

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