Toluenesulfonyl isocyanates 3 + 2 cycloaddition reactions

N-SulfonyIcarbamyloxypyridinium betaines from sulfonylisocyanates. Pyridine N-oxide in abs. benzene mixed with p-toluenesulfonyl isocyanate in the same solvent whereupon an exothermic reaction precipitates the product l-(p-toluenesulfonylcarbamyloxy)pyridinium betaine. Y 90%. — No 1,3-dipolar cycloaddition occurs. 

Electrophilic attack also occurs at the -Y-position of propargyl ligands, and this reaction converts propargyl complexes to allene complexes. An example of this protonation process is shown in Equation 12.61. This reaction has been used to initiate cycloaddition reactions. An example of this type of cycloaddition is the [3-t2] reaction of p-toluenesulfonyl isocyanate with the propargyl complex in Equation 12.62. Propargyl and Ti -allyl ligands are about equally reactive toward such cycloadditions. 

The [2+2] cycloaddition reaction of isocyanates proceeds better with olefins having electron donating groups attached to the double bond system. Examples include vinyl ethers, enamines, ketene acetals, tetraalkoxy- or tetraalkylaminooleflns. The more reactive sulfonyl and carbonyl isocyanates undergo cycloaddition reactions with vinyl ethers especially well. For example, the reaction of vinyl ethers with p-toluenesulfonyl isocyanate affords the [2+2] cycloadducts in a stereospecific reaction... 

The reaction of 2-phenylimino-l,3-thiazine 119 with tosyl isocyanate proceeds via a [2+2] cycloaddition across the the C=N bond to give 2-(p-toluenesulfonyl)imino-l,... 

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