Zinc-copper couples Reformatsky reactions

Several techniques have been used to activate the zinc metal and improve yields. For example, pretreatment of zinc dust with a solution of copper acetate gives a more reactive zinc-copper couple.168 Exposure to trimethylsilyl chloride also activates the zinc.169 Wilkinson s catalyst, RhCl(PPh3)3 catalyzes formation of Reformatsky reagents from diethylzinc, and reaction occurs under very mild conditions.170... 

Reformatsky reaction. The Reformatsky reaction of ethyl bromoacetate with several aldehydes and ketones proceeds in improved yields when the zinc is replaced by Le Goff s zinc-copper couple (1, 1020). THF is usually superior to ether as solvent. ... 

Intramolecular Reformatsky-type reactions a-methylene-t-lactones. Reaction of the (Z)-bromoaldehyde (1) in a dilute solution of THF with zinc dust at 65° or with zinc-copper couple at 25 leads to the c/i -fused a-methylene-y-lactone (2) in 60-62% yields. The reaction involves an intramolecular Reformatsky-type reaction followed by spontaneous lactonization. The same product (2) is also obtained from the (E)-isomer of (1) in 46% yield together with the transfused isomer of (2). The reaction of (1) with bis(l,5-cyclooctadicnc)nickel (4, 33-35 5, 34-35) also yields (2) in 527 yield. It is obtained in comparable yield... 

The Reformatsky reagents are the compounds of a a-haloester with zinc. Further, with the compounds of /(- or y-haloester with zinc the coupling reactions are able to proceed in the presence of catalysts such as palladium, copper and nickel compounds. These reactions are called the Remote Reformatsky reactions. For example, the reaction with palladium catalyst is shown in eq. (5.24) [42],... 

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