Zinc enolates alkyne addition reactions

Recently, Nakamura and coworkers described a related reaction of the zinc enolates derived from /3-aminocrotonamides of type 395256. In the presence of a stoichiometric amount of Et2Zn, the latter underwent smooth addition to terminal alkynes upon heating in hexane and afforded the corresponding tetrasubstituted 2-alkylidene acetoacetamides 396 (after acidic hydrolysis of the imine) with high (Z)-stereoselectivity (equation 173). 

A novel use of a wide range of nitriles as mediator has enabled the regioselective inter-molecular addition of unstabilized zinc ester enolates to 1-alkynes and l.S-enynes. " This reaction was made possible by a reversible addition of enolates to a nitrile (Blaise reaction), generating a zinc aza-enolate that, unlike zinc ester enolates, can add inter-molecularly to 1-alkynes and 1,3-enynes. Subsequent removal of the nitrile through a retro-Blaise reaction has generated the targeted addition product. 

---