A Competition between 1,3-Dipolar Cycloaddition and Substitution of Trifluoroacetonitrile Oxide

Trifluoroacetonitrile oxide reacted with conjugated olefins such as styrenes, indenes, and acyclic conjugated dienes to give not only the cycloadduct but also its linear isomeric oxime. Methyl or phenyl group attached to the unsaturated carbon of the dipolarophiles was found to favor the formation of oxime. Such a concomitant reaction was interpreted in terms of a competition between a concerted cycloaddition and a two-step substitution through an electrophilic attack of nitrile oxide. Similar competitions were also investigated with cyclic conjugated dienes, where the competitive ratio of the products was found to depend on the ring size.