An Unexpected Equilibrium Process Associated with a Standard Approach to Ynone Synthesis.

A direct comparison between Weinreb amides and morpholine amides was made with regard to their reactions with alkynyllithium reagents to form ynones. While treatment with stoichiometric alkynyllithium generally effects complete reaction in the case of Weinreb amides, incomplete reactions are obtained from the corresponding morpholine amides. This difference is attributed to an unexpected equilibrium process in the latter case, and it is shown that the use of excess alkynyllithium reagent with morpholine amides provides a synthetically useful synthesis of ynones at 0 °C.