The development of a new molybdenum-catalyzed procedure for the formation of oxazineshetero-Diels−Alder adductsfrom primary aromatic amines, hydrogen peroxide, and conjugated dienes is presented. The method is based on a molybdenum−peroxo complex, which in the presence of hydrogen peroxide as the terminal oxidant selectively catalyzes the oxidation of primary aromatic amines to the corresponding dienophilic nitroso compounds. The molybdenum−peroxo catalyst is under the present reaction conditions not reactive toward conjugated dienes and substituents attached to the aromatic nuclei of the primary aromatic amines. Several oxazines are synthezised following this new procedure using primary aromatic 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 several oxazines using different alkyl- and phenyl-substituted conjugated dienes and 4-chloroaniline as precursor for the dienophile. Moderate diastereomeric excesses are found when the reaction is carried out with 1-(2-aminophenyl)ethanol and 1,3-cyclohexadiene or (E)-1-phenyl-1,3-butadiene. The stereochemical and electronic factors governing the reaction course are briefly discussed.
|Tidsskrift||The Journal of Organic Chemistry|
|Status||Udgivet - 23 aug. 1996|