Propargylic zinc halide

Interestingly, silylated propargylic zinc reagents, such as 342, may be better viewed as the allenic zinc reagent 343 which reacts with an aldehyde via a cyclic transition state, affording only the a f/-homopropargylic alcohol 344 with 90% yield (Scheme 91) 22. Alkylzinc halides react only sluggishly with aldehydes or ketones. This reactivity can be... 

Aryl and vinyl zinc halides undergo clean reaction with 3-exomethylene tetrahydrofurans of type 38 in the presence of PdlPPhsla to furnish 2,3-dihydrofurans under desulfonylation (Scheme 41) <2000EJ01711>. The starting materials are easily prepared from propargyl alcohol and a sulfonyl cinnamate. 

In the presence of catalytic quantities of zinc halides, propargyl halides are converted into allenyl cations these undergo stepwise [2 + 2] or [3 + 2] cycloaddition to olefins to furnish moderate yields of a-halobenzylidenecyclobutanes or 1-halocyclopentenes depending on the substitution pattern of the propargyl halide (Scheme 29). ... 

Reisse used activated zinc for aqueous Barbier-type reactions.66 Submicromic zinc powder produced by pulsed sono-electroreduction is about three times more effective than the commercial variety. The stereochemical course of the allylation and propargylation of several aldehydes with crotyl and propenyl halides using zinc powder as the... 

Reaction of Zinc-Copper Couple with Propargyl Halides to Give Allenes... 

Allenyl cations. In the presence of a zinc chloride-ether complex allenyl cations (a) can be generated from a propargyl halide such as (1). The cation can undergo either [3 + 2]- or [2 + 2]cycloaddition with an alkene. When the R group is aryl, [2 + 2]cycloaddition is the major pathway (2) when R is CHj or C,H3, [3 + 2]-cycloaddition becomes the major reaction (3) (equation 1).1... 

Direct treatment of propargyl halides with /3-dicarbonyl compounds and subsequent treatment of the products with zinc carbonate yields 2,3,5-trisubstituted furans. ... 

It has proven possible to couple alkynyl iodides and bromides with a wide variety of zinc cyanocuprates. Coupling tolerates a number of functional groups on both the alkyne and the cuprate, including alkynyl ethers and propargyl ethers (equations 46 and 47). The cuprate partners have been primary alkyl, vinyl and aryl based59-61, whereas secondary alkyl organometallics couple in some cases and reduce the alkynyl halide in others. 

Allylic, benzylic, propargylic, and related organic halides react with many aldehydes and ketones in the presence of zinc to form alcohols. This reaction (the Zaitsev reaction) has been used in the synthesis of alcohols containing unsaturated groups. For example,... 

Propargyl halides also react with carbonyl compounds in the presence of zinc powder in concentrated aqueous salt solutions to give homopropargylic alcohols with high selectivity. High yields are obtained with aromatic and aliphatic aldehydes whereas ketones react only partially [1081. 

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