Alkenyl chlorides with Grignard reagents

Trisubstituted alkenes.9 A stereoselective synthesis of trisubstituted alkenes uses (E)-alkenyl sulfoxides (1)>U as the starting material. These are reduced to the corresponding sulfides (2)," which undergo coupling with Grignard reagents in the presence of complexes of nickel chloride and phosphines as catalyst.12 The products (3) are obtained in steroisomeric purity of > 99%. 

Base-catalyzed elimination of -acetoxy sulfones is highly stereoselective, leading to ( )-alkenyl sulfones which undergo transition metal-catalyzed coupling with Grignard reagents with retention of configuration to provide a stereoselective synthesis of trisubstituted alkenes. Either nickel(II) acetylacetonate, tris(acetylacetonato)iron(III), or iron(III) chloride can be used as the catalyst (eq 17). ... 

Aryl and alkyl organozincate reagents, generated in situ by reaction of Grignard reagents and sub-stoichiometric amounts of ZnCl2, cross-couple smoothly in refluxing THF with functionalized aryl and alkenyl as well as primary and secondary alkyl chlorides in the presence of Pd(dppf)Cl2. ... 

In 1971, Tamura and Kochi described the reaction of aUcyl Grignard reagents with alkenyl bromides in the presence of iron(III) chloride in THF. Only very reactive snbstrates such as vinyl and propenyl bromide were nsed (Scheme 16). Yields of conpling product are moderate to good but, unfortunately, a large excess of alkenyl bromide is required (3 to 9 equivalents). ( )-Bromopropene reacts 15 times faster than the (Z)-isomer. It should be noted that the reaction is stereoselective. 

In 2002, Figad re and coworkers reported the mono-reduction of 2-aryl (or heteroaryl)-1,1-dibromo-l-alkenes (Scheme 23). The reaction is achieved with one equivalent of isopropylmagnesium chloride in the presence of iron(III) acetylacetonate. Pure ( )-alkenyl bromides are obtained. With two equivalents of alkyl Grignard reagent, the mono-substituted product is obtained in moderate yield. 

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