PHOTOCHEMISTRY OF ACYLAZIDES .8. DO ACYLN ITRENES REACT LIKE 1,3-DIPOLES

The formation of three- ore five-membered heterocyclic rings by the re action of acylnitrenes with olefins depends on the electron density at the double bond. The generally expected formation of aziridines by a cheletropic reaction was observed by photolysis of aroylazides 1 in th e presence of 2,5-dihydrofuran 2. But with enolethers 3 and 4 oxazolin es were directly formed. This [3 + 2] cycloaddition is regiospecific. The cycloadditon is modestly stereoselective by steric hindrance withi n the cyclic enolether 3b. Very small de-values were found with chiral substituents in the acylazide 13. The azide decomposition was also ac hieved by photoinduced electron transfer. The same cycloaddition produ cts as obtained by direct photolysis of the azides were obtained via r adical anions of the acylazide. Using Michler's ketone as electron don or in the triplet state the formation of isocyanate which diminishes t he yield of cycloadducts can be avoided.