Alkenylchromium compounds

Coupling of vinyl iodides with aldehydes (12, 137). Further study1 of this 1,2-addition of alkenylchromium compounds to aldehydes to form allylic alcohols indicates that the reaction is applicable to a-alkoxy and a,(i-bisalkoxy aldehydes by use of a solvent other than DMF, which can promote elimination to an enal. A wide number of other functional groups can also be accommodated. Both vinyl iodides and p-iodo enones can be used as precursors to the alkenylchromium reagent. The reaction is only modestly diastereoselective, but the stereochemistry of a disubstituted vinyl iodide is retained. 

Alkenylchromium compounds. Addition of CrCh to a vinyl iodide or bromide in DMF forms a vinylchromium compound that adds selectively to aldehydes to form an ally lie alcohol. CrCl, also effects addition of iodobenzene to aldehydes to form benzyl alcohols. 

The ability of the anhydrous chiomiuin(n) ion to reduce vinyl halides and provide alkenylchromium compounds which participate in aldehyde addition reactions was first described by Takai and cowoik-ers. Treatment of 2-iodopropene (173) and benzaldehyde with anhydrous chromium(II) chloride in DMF afforded allylic alcohol (174) in quantitative yield (equation 62). ... 

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