Arylsulfonyl isothiocyanates

The preparation of thiiranes is most conveniently performed in solution. However, there are also protocols reported for reaction in the gas and solid phase. By using diazo and thiocarbonyl compounds in ether as solvent, both alkyl and aryl substituted thiiranes are accessible. As indicated earlier, aryl substituents destabilize the initially formed 2,5-dihydro-1,3,4-thiadiazole ring and, in general, thiiranes are readily obtained at low temperature (13,15,35). On the other hand, alkyl substituents, especially bulky ones, enhance the stability of the initial cycloadduct, and the formation of thiiranes requires elevated temperatures (36 1,88). Some examples of sterically crowded thiiranes prepared from thioketones and a macro-cyclic diazo compound have been published by Atzmiiller and Vbgtle (106). Diphenyldiazomethane reacts with (arylsulfonyl)isothiocyanates and this is followed by spontaneous N2 elimination to give thiirane-2-imines (60) (107,108). Under similar conditions, acyl-substituted isothiocyanates afforded 2 1-adducts 61 (109) (Scheme 5.23). It seems likely that the formation of 61 involves a thiirane intermediate analogous to 60, which subsequently reacts with a second equivalent... 

L abb6 and co-workers have found that 4-alkyl-5-sulfonylimino-A2-l,2,3,4-thiatriazolines 165 can be easiliy prepared by reaction of the highly reactive arylsulfonyl isothiocyanates 166 with alkyl azides (Equation 15). Kinetic experiments indicate that the reaction between picryl isothiocyanate and alkyl azides is probably concerted since no significant solvent effect has been observed <1973JOC2916, 1974JA3973>. This is in support of the postulated mechanism involving the intermediate 5-imino-A2-l,2,3,4-thiatriazolines 164 in the reaction of isothiocyanates with hydrazoic acid. 

Alkyl azides readily undergo 1,3-dipolar cycloaddition to arylsulfonyl isothiocyanates (375) to yield thiatriazolines (376). Thermolysis of (376) in the presence of isocyanates or carbodiimides produces 1,2,4-thiadiazole derivatives (378) and (379), respectively. The intermediate formation of a thiaziridinimine (377) has been postulated as indicated in Scheme 137 (75JOC1728, 75S52). The use of isothiocyanates as dipolarophiles produces dithiazolidines (380) instead of the thiadiazole derivatives. In these reactions the intermediate thiazirine (377) functions as a 1,3-dipole with the positive charge primarily localized on sulfur. It was recently proposed that the reaction of oxaziridines (381) with isothiocyanates produces a similar thiazirine intermediate (382) which reacts in a different regiospecific manner with isothiocyanates to produce 1,2,4-thiadiazole derivatives (383) and (384 Scheme 138) (74JOC957). 

Bis(imino) thietanes, 343, 344, are prepared by reaction of isonitriles with iminothiiranes or of ketenimines with p-tolylsulfonyl isothiocyanate. Reaction of phosphonium ketimine ylides, for example, 312, and related compounds with isothiocyanates also gives bis(imino) thietanes, for example, 345. " Treatment of arylsulfonyl isothiocyanates with trimethylacetoisonitrile yields tris(imino)-thietanes, for example, 341. ... 

Dickore and Kuhle have utilized this type of reaction to prove the structure of arylsulfonyl isothiocyanate dimers (CIII). 

Organic azides like alkyl azides and TMSA (146) are also able to add to isothiocyanates. Alkyl azides 189, namely -butyl azide or benzyl azide, react with an equimolar amount of arylsulfonyl isothiocyanates 190 at room temperature in carbon tetrachloride or without solvent during 7 hours up to 2 days to exclusively afford 4-alkyl-5-arylsutfonylimino-l,2,3,4-thiatriazolines 191 in 50-75% yield. The product was the result of a [3+2]-cycloaddition to the C=S bond of the isothiocyanate moiety. Upon heating to 45-80 °C in inert solvents, the 4-alkyl-5-arylsulfonylimino-l,2,3,4-thiatriazolines 191 evolve nitrogen and sulfur, decomposing to sulfonylcarbodiimides 192 which are valuable precursors for the synthesis of further heterocycles like 4-amino-thiazolidines or thiazolines (Scheme 37) [139,140]. 

Scheme 37 Reaction of alkyl azides 189 with arylsulfonyl isothiocyanates 190 to yield 4-alkyl-5-arylsulfonylimino-l,2,3,4-thiatriazolines 191. Thermal decomposition of the latter results in the formation of sulfonylcarbodiimides 192 [139,140]...

Arylsulfonyl isothiocyanates react with aliphatic azides across their C=S bonds to give thiatriazolines 130... 

In contrast to the acylation with carboxylic acid chlorides, secondary 1,1-enediamines react with isocyanates and isothiocyanates to give cleanly the /7-carbon acylated products. Carbamoyl-substituted enediamines (175) have been obtained from 174 and arylsulfonyl isocyanates (equation 67)140,141. 

In their reactivity with azides, acyl isothiocyanates occupy a position intermediate between the active arylsulfonyl and the more sluggish aryl isothiocyanates (see above). The interaction of alkyl azides and benzoyl... 

Also, A-(arylsulfonyl)aziridines 97 react with isothiocyanates to give the [3+2] cycloadducts 98. In this reaction the isothiocyanate undergoes reaction across its C=S bond . In contrast, substituted A-(arenesulfonyl)aziridines, in the presence of sodium iodide as the catalyst, undergo [3+2] cycloaddition reactions with aryl isothiocyanate across their C=N... 

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