Tosyl isothiocyanate 4+2 cycloaddition reactions

A successful method for preparing 1,3-thiazetidines is the cycloaddition of carbodiimides with isocyanates. The cycloadduct 151 was derived by the interaction of carbodiimide 152 and tosyl isothiocyanate . Reaction of 152 with methyl or phenyl isothiocyanate preferentially leads to iminotriazine-thiones. Cycloaddition between aryl isothiocyanates and dicyclohexylcar-bodiimide produced 153. ... 

The more reactive tosyl-, alkoxycarbonyl- and mercaptocarbonyl isothiocyanates undergo a [2+2] cycloaddition reaction with azomethines (R = i-Pr, CeHn, Ph) across their C=S bonds to give 1,3-thiazetidine derivatives 42 (R = 4-MePhS02-, MeSCO-, EtOCO-)22. 

Likewise, imidoyl ketenimines 153 react as 1-aza-1,3-dienes in [4-1-2] cycloaddition reactions with phenyl isocyanate to give the cycloadducts 154 (62-67 % yields) or with tosyl isothiocyanate to give the cycloadducts 155 (62-69 % yields) . ... 

When acrylonitrile or ethyl acrylate was used as the dipolarophile, the azomethine adducts (134) and (135) were formed no thiocarbonyl ylide addition products were isolable in refluxing toluene or xylene, although the isoindoles (136a) and (136b) derived from them were isolated. In contrast to the reactions with fumaronitrile or AT-phenylmaleimide, the azomethine adducts (134) and (135) were still present at higher reaction temperatures — almost 50% in toluene and 4-5% in xylene. Under the same reaction conditions other electron-deficient dipolarophiles like dimethyl fumarate, norbornene, dimethyl maleate, phenyl isocyanate, phenyl isothiocyanate, benzoyl isothiocyanate, p-tosyl isocyanate and diphenylcyclopropenone failed to undergo cycloaddition to thienopyrrole (13), presumably due to steric interactions (77HC(30)317). 

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