Studies Dealing with the Aza-Claisen Rearrangement of 2-Allyloxy-Substituted Oxazoles

Article abstract of DOI:10.1021/jo00177a001

The scope of the thermal <3,3>-sigmatropic rearrangement of a number of 2-allyloxy-substituted 4,5-diphenyloxazoles has been examined.These systems undergo a facile aza-Claisen rearrangement to give 3-allyl-substituted 4,5-diphenyl-4-oxazolin-2-ones.In contrast to the thermal results, irradiation of the 2-allyloxy- or benzyloxy-substituted oxazole gave rise to a mixture of 3- and 5-substituted oxazolinones.The photolysis proceeds via C-O bond scission to generate a radical pair which subsequently recombines to produce the mixture of oxazolinones.A series of related oxazoles was prepared in which the heterocyclic ring and the ? bond are connected by an alkoxy side chain.All attempts to induce an intramolecular Diels-Alder reaction failed.The only product that could be obtained corresponds to that derived from an intramolecular ene reaction.The excited-state behavior of several 2- and 5-allyloxy-substituted oxazoles was also studied.The rationale for the difference in thermal and photochemical behavior is discussed.