Phenylcarbonyl isocyanate 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. 

Across carbon multiple bonds The reaction of acetylenes with phenylcarbonyl isocyanate affords the expected [2+2] cycloadduct 56 . However, the assigned structure is in doubt because MNDO results suggest that it is impossible to prepare the unsaturated )8-lactams by [2+2] cycloaddition of acetylenes with acyl isocyanates . In other acetylene reactions with isocyanates the [2+2] cycloadducts are only postulated as intermediates. 

Acylketenes, generated in the thermolysis of 4-oxo-l,3-dioxine derivatives, react with phenylcarbonyl-, methoxycarbonyl-, or phenoxycarbonyl isocyanates by a [4+2] cycloaddition reaction to give 2,4-dioxo-l,3- oxazines. ... 

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. 

---

See also in sourсe #XX -- [ ]

---