Science of Synthesis

Mejuch, T.; Marek, I., Science of Synthesis: Cross Coupling and Heck-Type Reactions, (2013) 1, 766.

Organozinc halide reagents can be prepared via the direct insertion of zinc metal into the carbon—halogen bond of organic halides. This method was introduced by Frankland in 1849.[‌8‌] Alkyl iodides are typically used for this purpose. The insertion of zinc into sp2 carbon—halide bonds is more difficult, requiring harsher reaction conditions and the use of a polar solvent.[‌9‌] Knochel and co-workers have discovered that a zinc–lithium chloride complex facilitates zinc insertion into sp2 carbon—bromine bonds under mild conditions, yielding the desired alkenylzinc reagent.[‌10‌] The presence of functional groups, such as carbonyl moieties, adjacent to the double bond can facilitate the addition of zinc and even allow the use of less reactive alkenyl chlorides.[‌11‌] More complex structures can also be prepared by zinc insertion into (1-iodoalkenyl)boronic esters in dimethylacetamide to furnish bimetallic 1-borylalk-1-enylzinc species (‌Scheme 2‌).[‌12‌]

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References