Zinc enolates Blaise reaction

This chapter summarizes studies on the nature of the Reformatsky reagent as well as other, related, zinc enolates and outlines the synthetic aspects of the reaction with aldehydes and ketones. In addition, reactions of the Reformatsky reagent with imines and nitriles (the Blaise reaction) are described. 

There are several condensation reactions that use zinc enolates rather than sodium, magnesium, or lithium enolates. These are usually categorized as a classical Reformatsky reaction or as a modified Blaise reaction. 

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. 

Non-stabilized zinc ester enolates (463) (Reformatsky enolates) have been reported to add to terminal alkynes (465) in the presence of nitriles RC=N, affording (467). The reaction is initiated by the Blaise reaction of (463) with the nitrile, which generates the zinc chelate (464). The latter species then adds to the alkyne (465) in a Markovnikov manner, and the resulting intermediate (466) undergoes a retro-Blaise fragmentation to afford the zinc enolate (467) and the original nitrile. When combined with aDiels-Alder reaction partner and subsequent oxidative aromatization, this sequence can serve as a one-pot de novo construction of a-arylated alkanoates. " ... 

---