Reaction with vinylic halide

The procedure described here Is an example of a general method for preparing conjugated alkadienes by the palladium-catalyzed reaction of 1-alkenylboranes or boronates with vinylic halides. Hydroboratlon of l-a1kynes with catecholborane Is a standard method for obtaining (E)-l-alkenylboronates (1). Several different types of alkenylboranes and boronates (2-4) are now available as reagents for the cross-coupling reaction with vinyl halides. 

Some success has been achieved using all of the above olefinic compounds in reactions with vinylic halides and amines to add the number of carbons indicated, selectively to form one isomeric product or one which is separated easily from a mixture that may have been formed. Numerous other similar reagents may be imagined, but either they have not been tried or successful reactions were not found. 

Additions to functionalized three-carbon olefins have been studied extensively. We have used methyl acrylate as a standard olefin since it always reacts only at the terminal carbon and the a,/3-double bond in the product is always trans. The stereospecificity of its reactions with vinylic halides varies with structure. The simple 1-halo-l-alkenes with methyl acrylate under normal conditions give mixtures of E,Z- and E,E-dienoates. The reaction is more selective with the bromides than with the iodides and the stereoselectivity increases with increasing triphenylphosphine concentration. This occurs because the excess phosphine displaces the hydridopalladium halide group from the diene 7r-complex before readdition to form the ir-allylic species occurs (see Equation 6). The disubstituted vinylic bromides react stereospecifically with methyl acrylate (4). 

Isocoumarins. Isocoumarins can be prepared from benzoic acids by orf/jo-thal lation followed by olefination promoted by PdCI. Reaction with simple alkenes requires 1 equiv. of PdCb and a base-catalyzed reaction to effect the final cyclization. The reaction with vinyl halides or acetates generates isocoumarins directly and requires only catalytic amounts of PdCT. 

Coupling reactions with vinyl halides are stereospecific. For example, reaction of trans-1 -bromo-1-hexene with (CH3)2CuLi forms rrara-2-heptene as the only stereoisomer (Equation [3]). 

Substitution reactions of sp halides have been achieved with the aid of a palladium catalyst (Scheme 23). 14,19 variety of aryl bromides and iodides serve as electrophiles. Reactions with vinyl halides are stereospecific. Vinyl trifluoromethanesulfonates (triflates) also react rapidly with homoenolates. 

Ene reactions. The antimony pentafluoride—methyl fluoride complex in SO2 undergoes the ene reaction with vinyl halides (1) at -65 to give unsaturated methyl sulfinates (2), isolated after addition of methanol. Yields... 

Under carefully optimized conditions nickel complexes have shown excellent performance in the catalytic cross-coupling reactions. The possibility of Ni catalysis in Csp -S bond formation was first shown by Cristau et al. in 1981 [15]. The reaction of Ar2S formation was carried out with NiBr2 as a catalyst precursor and o-(Ph2P)2C6H4 as a ligand. The same authors have shown the possibility of the cross-coupling reaction with vinyl halides (Scheme 3.19) [46]. 

Macnaughtan ML, Johnson MJA, KampfJW. Olefin Metathesis Reactions with Vinyl Halides Formation, Observation, Interception, and Fate of the Ruthenium-Monohalomethylidene Moiety.JHm Chem Soc. 2007 129(25) 7708-7709. 

Even simple alkenes, such as 1-hexene 9.270, can yield ir-allyl complexes on reaction with vinyl halides under Heck conditions (Scheme 9.75). This is only apparent when a nucleophile is present, such as a secondary amine or a malonate anion. The ir-allyl complex 9.279 is generated by isomerization of the corresponding T -complex 9.278 that is itself generated by a -hydride elimination-reinsertion sequence from the initial insertion product 9.275. Nucleophilic attack on the Tr-allyl complex gives the three component coupling product 9.273, while the Heck product, diene 9.272, can arise from dissociation from t -complex 9.276 or p-hydride elimination from the -intermediate 9.278. Again, the reaction is particularly effective in an intramolecular sense. °°... 

Ethynylcopper reagents couple in dipolar solvents with various aromatic halides. The reaction can be used effectively for heterocyclic synthesis (Gump et al., 1967 Castro et al., 1966, 1969). The reaction with vinylic halides is also... 

Reaction with Vinylic Halide. Synthesis of Conjugated Alkadienes... 

The stereochemistry of the double bond is retained in the reaction with vinylic halides. 

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