A MOLYBDENUM-CATALYZED OXIDATIVE SYSTEM FORMING OXAZINES (HETERO-DIELS-ALDER ADDUCTS) FROM PRIMARY AROMATIC-AMINES, HYDROGEN-PEROXIDE, AND CONJUGATED DIENES

The development of a new molybdenum-catalyzed procedure for the format ion of oxazines-hetero-Diels-Alder adducts-from primary aromatic amine s, hydrogen peroxide, and conjugated dienes is presented, The method i s based on a molybdenum-peroxo complex, which in the presence of hydro gen peroxide as the terminal oxidant selectively catalyzes the oxidati on of primary aromatic amines to the corresponding dienophilic nitroso compounds. The molybdenum-peroxo catalyst is under the present reacti on conditions not reactive toward conjugated dienes and substituents a ttached to the aromatic nuclei of the primary aromatic amines. Several oxazines are synthezised following this new procedure using primary a romatic amines having either electron-withdrawing or electron-donating substituents and 1,3-cyclohexadiene as the standard diene. The scope of the new procedure is also demonstrated by the preparation of severa l oxazines using different alkyl- and phenyl-substituted conjugated di enes and 4-chloroaniline as precursor for the dienophile. Moderate dia stereomeric excesses are found when the reaction is carried out with 1 -(2-aminophenyl)-ethanol and 1,3-cyclohexadiene or (E)-1-phenyl-1,3-bu tadiene. The stereochemical and electronic factors governing the react ion course are briefly discussed.