Direct Organocatalytic Asymmetric Mannich Addition of 3‐Substituted‐2H‐1,4‐Benzoxazines: Access to Tetrasubstituted Carbon Stereocenters

Substituted-2H-1,4-benzoxazines under- go a highly enantioselective direct Mannich reac- tion with acetone in the presence of an l-proline catalyst at room temperature. The corresponding N-heterocycles with a-tetrasubstituted carbon ste- reocenters were obtained in good yields (48-92%) and excellent enantioselectivity (up to > 99% ee). Furthermore, a novel modification involving the diastereoselective reduction of the Mannich adduct was carried out leading to the formation of a 1,3- amino alcohol with a chiral tetrasubstituted carbon stereocenter in high yield.