Phenylcarbonyl isothiocyanate 4+2 cycloaddition reactions

Cycloaddition Reactions. In [2+2] cycloaddition reactions with car-bodiimides sometimes [2+4] cycloadducts are produced as coproducts. Examples include the reaction of phenylcarbonyl isocyanate, phenylcarbonyl isothiocyanate and thiocarbamoyl isothiocyanate with carbodiimides to give [2+4] cycloadducts, discussed in Section 5.3.1. In the current section, mainly [2+4] cycloaddition of carbodiimides as dienophile with dienes derived from oxoketenes, generated in situ or masked oxoketenes, especially 2,3-diones investigated by Kollenz and his coworkers are discussed. 

Similar [3+2] cycloaddition products are obtained in the reaction of 104 with 4-nitrophenyl isothiocyanate and phenylcarbonyl isothiocyanate. 

Nitrones undergo the [3+2] cycloaddition reaction mainly across the C=N bond of the isothiocyanate. For example, C-phenyl-N-methylnitrone 109 reacts with phenyl isoth-iocyanate " and phenylcarbonyl isothiocyanateto give l,2,4-oxadiazolidine-5-thiones 110. 

Cyclic aldo- and ketonitrones react similarly with phenyl isothiocyanateHowever, substituted phenyl isothiocyanates react with 5,5-dimethyl-l-pyrroline-l-oxide to give cycloadducts derived from addition across the C=N bond as well as the C=S bond of the isothiocyanates. The C=S cycloadducts are unstable and undergo further transformations . The [3+2] cycloaddition reaction of 3,3,5,5-tetramethylpyrroline-l-oxide with aryl- and phenylcarbonyl isocyanates also occurs exclusively by addition across the C=S bond . ... 

Cycloadditions The [4+2] cycloaddition reactions of carbodiimides with phenyl-carbonyl isocyanate, phenylcarbonyl isothiocyanate and thiocarbamoyl isothiocyanate have been discussed above. In the dimerization reactions the functional carbodiimides react as both the diene and the dienophile. Unsaturated carbodiimides, generated in situ, can be trapped with N=N bond- or C=N bond-containing substrates. 

The [2+2] cycloaddition reaction of isothiocyanates with ketenimines proceeds at room temperature across the C=S bond of the isothiocyanates and the C=C bond of the ketenimines to give 2,4-bis(imino)thietanes. However, only reactive isothiocyanates, such as arenesulfonyl isothiocyanates (48-54 % yield) or phenylcarbonyl isothiocyanate (44 % yield), undergo this reaction... 

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See also in sourсe #XX -- [ , , , ]

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