Induced conjugate addition of simple 2-lithio-1,3-dithians to cyclic αβ-unsaturated ketones

In sharp contrast to prior observations that 2-lithio-1,3-dithians undergo only carbonyl (1,2-) additions to enones, the successful conjugate (1,4-) addition of the parent 2-lithio-1,3-dithian and its simple derivatives has been achieved by the addition of 1·0-2·0 equiv. of hexamethylphosphoramide to the reaction mixture.