STUDY ON STEREOCHEMISTRY OF THE 1,3-DIPOL E CYCLOADDITION REACTION OFSOME 5-PHENYL-3,6-DIHYDRO-2H-1,4-OXAZIN-2-ONES WITH N-METHYLMALEIMIDES AND N-PHENYLMALEIMIDES

Six derivatives of 5-phenyl-3,4-dihydro-2H-1,4-oxazin-2-ones 1 were sy nthetized from alpha-amino acids. These compounds are precursors of si x-membered cyclic azomethine ylids involving one stereocenter. The 1,3 -dipolar species react with N-methyl and N-phenylmaleimides, leading d iastereospecifically to cycloadducts where the approach of the dipolar ophile occurs from the less hindered side of the 1,3-dipole and with t he maleimido moiety in an exo position. Unfortunately, racemization wa s observed during the cycloaddition reaction, presumably owing to reve rsible imine-enamine transformation.