Zinc, organozinc carbenoid preparation

Functionalized zinc carbenoids have been prepared from carbonyl compounds by an indirect strategy. The deoxygenation of a carbonyl compound to an organozinc carbenoid can be induced by a reaction with zinc and TMSCl. Therefore, the aldehyde or ketone, when treated with TMSCl or l,2-bis(chlorodimethylsilyl)ethane in the presence of an alkene, generates the cyclopropanation product. This method is quite effective for the production of alkoxy-substituted cyclopropane derivatives. A 55% yield of the... 

Recently, even organozinc carbenoids have been used for the preparation of vinylcyclo-propanes. These species are formed upon reaction of zinc with an aldehyde or ketone in the presence of 1,2-bis(dichlorodimethylsilyl)ethane. A synthetic procedure that avoids competitive carbonyl coupling has been developed the carbonyl compound is added to a refluxing mixture of the reagents, namely amalgamated zinc, the silyl chloride and two equivalents of the alkene. 

Insertion of zinc into the carbon-halogen bond of organozinc carbenoids is accelerated by the presence ofa catalytic amount of Pb(II) salts [40]. By this means, several l,l-(biszincio)alkane reagents such as 14,15 [41], or 16 [42] can be prepared (Scheme 4.4). The commercially available Nysted reagent 17 is also prepared through zinc insertion with zinc-lead couple [43]. In the case of aUcyl-substituted l,l-(biszincio)aIkanes, P-hydride elimination is prevented with the adjunction of TMEDA (N,N,N, N -tetramethylethylenediamine) [44]. 

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