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 alpha,beta-unsaturated carbonyl followed by metallacycle-mediated union of the resulting allylic alcohol with preformed trimethylsilane-imines (generated in situ by the low-temperature reaction of lithium hexamethyldisilazide 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.