Synthesis of unsaturated β-amino acid derivatives from carbamates of the Baylis–Hillman products

By treatment with a catalytic amount of DBU in DCM, N-p-toluenesulphonyl carbamates 6a–c, prepared starting from the corresponding Baylis–Hillman adducts, gave (E)-2-(p-toluenesulphonylaminomethyl)propenoates 3a–c, exclusively. On the contrary, changing DABCO for DBU, 2-methylene-3-p-toluenesulfonylamino esters 4a–f were obtained in good yield starting from N-p-toluenesulphonyl carbamates 6a–f. In analogy, N-acyl carbamates 9a–f were treated with DABCO in DCM to give the 2-methylene-3-acylamino esters 5a–f.