Three-Component Coupling Sequence for the Regiospecific Synthesis of Substituted Pyridines

A de novo synthesis of substituted pyridines is described that proceeds through nucleophilic addition of a dithiane anion to an α,β-unsaturated carbonyl followed by metallacycle-mediated union of the resulting allylic alcohol with preformed TMS-imines (generated in situ by the low temperature reaction of LiHMDS with an aldehyde) and Ag(I)-, or Hg(II)-mediated ring closure. The process is useful for the convergent assembly of di- through penta-substituted pyridines with complete regiochemical control