Reike powders

The zinc metal is typically activated before use and methods for accomplishing this have been reviewed. The use of highly reactive forms of zinc (Reike powders), obtained by reduction of zinc salts with an alkali metal, detracts from the convenience of the classical procedure but much higher yields have been obtained, at least with the simple substrates that have so far been examined. One of the most convenient preparations of a Reike powder uses sodium naphthalide, as shown in Scheme 4. Reactive zinc powders so allow the use of a-chloro esters which are unsatisfactory with the usual forms of... 

Cyclopentene anndation The Grignard derivative (2) of 1, prepared efficiently with Reike s magnesium powder (5,419), undergoes conjugate addition to enones in the presence of a copper(I) salt, particularly with CuBr-S(CH3)2 (6, 235). The adducts are converted to annelation products on treatment with aqueous THF containing HCl. 

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