Synthesis of 1,3-oxazine derivatives by palladium-catalyzed cycloaddition of vinyloxetanes with heterocumulenes. Completely stereoselective synthesis of bicyclic 1,3-oxazines

1,3-Oxazines were prepared by palladium-phosphine-catalyzed cycloaddition reactions of vinyloxetanes with heterocumulenes. 4-Vinyl-1,3-oxazin-2-imines were obtained in fine yields by the reaction of 2-vinyloxetanes with carbodiimides in THF at rt for 12 h using 1.5 mol % Pd-2(dba)(3). CHCl3 and 3 mol % bidentate phosphine ligands (dppe or dppp). When isocyanates were utilized in the reaction, moderate to good yields of 4-vinyl-1,3-oxazin-2-ones were achieved within 1-2 h at rt. Palladium-catalyzed cycloaddition of fused-bicyclic vinyloxetanes with heterocumulenes proceeds in a highly stereoselective fashion affording only the cis-3-aza-1-oxo-9-vinyl[4.4.0]decane derivatives in 43-98% yield.