Simple and selective one-pot replacement of the N-methyl group of tertiary amines by quaternization and demethylation with sodium sulfide or potassium thioacetate: an application to the synthesis of pergolide

The paper describes a mild, selective, and rapid replacement of an N-methyl group of tertiary amines with other alkyl groups via a simple one-pot procedure. This transformation is easily achieved by preparation of the appropriate quaternary ammonium salt in sulfolane and in situ treatment with sodium sulfide or potassium thioacetate. The protocol is successfully applied to the transformation of dihydrolysergol, dextromethorphan and laudanosine (as models of ergot and opium N-methyl alkaloids) into various A-alkyl congeners.