Zinc homoenolates substitution reactions

Among the characterized metal homoenolates, only zinc homoenolate of alkyl propionate undergoes substitution reactions with electrophiles under suitable conditions. Two types of metal catalysts, copper(I) and metals of the nickel triad (e.g. Pd), have successfully been used to effect allylation, arylation, and vinylation reactions. 

The formation of activated iminium intermediates derived from nitrogen heterocycles has been reported by Comins and co-workers.163,163a The activation of pyridine derivative with phenyl chloroformate provides pyridinium salt, which smoothly reacts with the zinc homoenolate (Equation (94)).163 163a 164 The reaction of unsaturated amide with Ph jC 1 BI 4 produces iV-acyliminium ions, which react with PhaZn in CH2CI2 producing the desired a--substituted amine (Equation (95)).165... 

The Pd- or Ni-catalyzed reaction of tiialkylsilylmethylmetals containing Zn or Mg provides a novel regio- and stereo-controlled route to allylsilanes [82-84] (Scheme 1-26). Another useful application of Pd-catalyzed alkylation is the / -substitution reaction of zinc homoenolates [85-89] (Scheme 1-27) and higher homologues [90]. 

---