Alkenyl iodides with Grignard reagents

In addition to Ni and Pd catalysts, Li2CuCU is also an effective catalyst for the coupling of alkenyl iodides with Grignard reagents. Since the stereochemistry of alkenyl iodides is also retained, the coupling reactions are useful for the stereoselective synthesis of disubstituted alkenes, - trisubstituted al-kenes, allylsilanes, allyl alcohols and tetrasubstituted alkenes (equations 25-29). ... 

The direct coupling of two unlike alkenyl groups, for example via vinylic cuprates and vinyl iodides, has not proved useful as a stereospecific process. However, Dang and Linstrumelle have now shown that stereospecific substitution (>97%) of alkenyl iodides with a variety of Grignard reagents can occur in high yield and under mild conditions, when catalysed with tetrakis(tri-phenylphosphine)palladium (Scheme 6). Linstrumelle and his co-workers have... 

The direct coupling of two unlike alkenyl groups by reaction of an alkenyl metal derivative with an alkenyl halide has in the past proved difficult. In the presence of a catalytic amount of [(Ph3P)4Pd], however, alkenyl iodides react stereo-specifically with Grignard reagents of the type (44) under very mild conditions to produce the dienes (45) in high yield (ca. 80%). ... 

In 2001, Cahiez, Knochel and coworkers reported an extension of this work to the coupling of functionalized aryhnagnesium compounds with alkenyl bromides or iodides (Scheme 20). It should be noted that with aryl Grignard reagents the use of NMP is not necessary. 

Dang, H. P., Linstrumelle, G. An efficient stereospecific synthesis of olefins by the palladium-catalyzed reaction of Grignard reagents with alkenyl iodides. Tetrahedron Lett. 1978,191-194. 

Vinyl, 1-alkenyl and 2-alkenyl Grignard reagents couple with alkyl bromides or iodides in the presence of CuP -or AgNOa the configuration of the alkenyl Grignard reagent is essentially... 

Alkenyl iodides are also readily alkylated by Grignard reagents under catalytic conditions to yield the corresponding alkenes with retention of the configuration of the double bonds (Scheme 3.65). Yields are usually higher than in the reaction with dialkylcuprates. Because alkenyl iodides themselves are readily obtained by a variety of procedures, the sequence provides a general route to di- or tri-substi-tuted alkenes. The reactive intermediate is believed to be a homocuprate. 

Fe(III) salts catalyse the coupling of Grignard reagents with alkenyl and aryl halides. The mechanism is not fully understood, but probably resembles the standard palladium sequence, through either an Fe(0)-Fe(II) or an Fe(I)-Fe(III) cycle. A particular feature is that chlorides are superior, in terms of yield, to bromides and iodides as substrates. Triflates also give very high yields and couple selectively in the presence of chlorides. Heterocyclic examples include 6-chloropurines, 4-chloropyrimidines, 6-chloro-l,3-dimethyluracil and 2-chloropyridines," and the dichloropyridine example below." ... 

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