Vinylzinc derivative

Hydroboration of alkynes R C=CR with Cy2BH, followed by transmet-allation with Mc2Zn, has been shown to produce ( )-vinylzinc derivatives... 

The impetus for the development of gem-bimetallics was initially to discover alkylidene-transfer reagents akin to Tebbe s reagent [14]. Schwartz prepared bimetallic aluminum—zirconocene derivatives by the hydrometallation of various vinyl metallic compounds [15—17]. Knochel has developed zinc—zirconium gem-bimetallics by hydrozircona-tion of vinylzincs and has used them as alkylidene-transfer reagents [18], More recently, other gem-bimetallics have been developed that exhibit different reactivities of the two carbon—metal bonds. Thus, Normant and Marek have reported the allylmetallation of vinyl metals to afford zinc—magnesium and zinc—lithium gem-bimetallics, which react selectively with various electrophiles such as ClSnBu3, H20, etc. [19, and references cited therein]. However, selective and sequential cleavage of the two carbon—metal bonds... 

SCHEME 65. Addition of vinylzinc bromide to miinium salts generated from benzotriazole derivatives... 

Fluorinated vinylzinc reagents readily react (particularly with Cu(I)X catalysis) with allyl halides at room temperature (equation 63)57. With a substituted allyl halide, the 2-propenyl reagent gave products of both a- and -attack. The predominant product is derived from attack at the less hindered position (equation 64)5. 

The palladium-catalyzed reaction of 2-bromocyclopentene-l-carbaldehyde derivatives with vinylzinc, 2-furyl, or 2-thienylzinc halides leads to the dimethylhydrazones which cyclize thermally to pyridines (Scheme 97) <1995T9119>. Palladium-catalyzed hetero-annelation reactions of internal alkynes to pyridines were reported... 

Diethylzinc catalyses allenylation of aldehydes and ketones by an allenyl boronate, via a site-selective B/Zn exchange a balance of allenyl and propargyl alcohols are produced. A mild enantioselective addition of vinylzinc reagents (derived from vinyl iodides and diethylzinc) has been reported, with wide tolerance of functional groups. 

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