Zincates preparation

It is liquefied by conducting the gas through a condenser cooled with ice water. Where difficult to obtain, it may be prepared by passing chlorine gas through a stirred suspension of sodium tetrakis(cyano-C)zincate prepared in situ from sodium cyanide and zinc sulfate. ... 

The chiral organocopper compound (186) adds diastereoselectively to 2-methyl-2-cyclopentenone, allowing the preparation of optically active steroid CD-ring building blocks (Scheme 68).202-204 A related method was applied to a synthesis of the steroid skeleton via an intramolecular (transannular) Diels-Alder reaction of a macrocyclic precursor.203 Chiral acetone anion equivalents based on copper azaeno-lates derived from acetone imines were shown to add to cyclic enones with good selectivity (60-80% ee, after hydrolysis).206-208 Even better ee values are obtained with the mixed zincate prepared from (187) and dimethylzinc (Scheme 69). Other highly diastereoselective but synthetically less important 1,4-additions of chiral cuprates to prochiral enones were reported.209-210... 

A solution (prepared at the boil) of 60 g. of ZnO and 250 ml. of pure, 51% sodium hydroxide is filtered at about 40 0, cooled to 15 °C, and seeded with zincate prepared as described under (A). After 12 hours the mixture is filtered and worked up as imder (A). Yield 40 g. 

Although the existence and structures of tetraorganozincates in the solid state are now well established, the reactivity patterns of these compounds in organic synthesis are still largely unknown. Homoleptic and heteroleptic tetrasubstituted dianionic zincates of the type [ZnR3X], X = Me, CN, SCN, were prepared as shown in Scheme 58... 

Similarly, alkenylzirconium species prepared by the hydrozirconation of alkynes add in a conjugated fashion to enones. Formation of an intermediate zincate prior to transmetalation to the copper species facilitates the Michael addition (Scheme 2.62) [135]. This methodology has been applied to the preparation of protected misoprostol 129 (Scheme 2.63) [136, 137]. 

Organomagnesium compounds react with imines, prepared from 3-methoxy-2-naphth-aldehydes by a 1.4-addition mechanism. This reaction can be performed with high diastere-oselectivity. The method was applied for the synthesis of optically pure S-tetralones . Vinyhnagnesium bromide reacts as an acceptor with a ketone dimethyl hydrazone zincate 207, yielding a 1,1-bimetallic species, which can be reacted sequentially with two different electrophiles (equations 131 and 132) . The reaction proceeds via a metalla-aza-Claisen rearrangement, where the dimethylhydrazone anion behaves as an aza-allylic system . 

In an approach similar to the synthesis of 12, the neopentyl derivatives [(Me3CCH2)3Zn] K(C6H6) (17) and [(Me3CCH2)3Zn]Na (18) have been prepared from the reaction of (Me3CCH2)2Zn and potassium and sodium, respectively. Also, the structures of these compounds were crystallographically determined and are closely related to the structures of the (trimethylsilyl)methyl zincates described above . 

SCHEME 54. Preparation and uses of zincates on the solid phase... 

Immobilized zincates such as 177 can be prepared by treating serine-bound 4-iodobenzoate with f-BusZnLi at They react readily with aldehydes. 

SCHEME 16. Preparation of ailyl- and benzylzinc derivatives by oxidative zincation... 

As shown in equation 53, when the zincated hydrazone, prepared from hydrazone by treatment with 2 equivalents of f-butyllithium and zinc(II) bromide, is treated with alkenylborane, the a-borylorganozinc is obtained with high diastereoselectivity. This pseudo-gem-dimetal species reacts with allyl halide stereospecifically. Through the transformation, three stereogenic centers are constructed diastereoselectively77. 

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