Reaction Conditions Bases, Solvents, and Additives

Since strong acids are formed, the reaction must be carried out in the presence of bases. Coordinating and polar solvents, such as DMF, MeCN, NMP and DMSO, are preferable solvents. DMF is the most widely used. Water, a highly polar liqvud, has been found to accelerate some reactions, which are carried out smoothly in aqueous solvents using water-soluble ligands. 

Poly(ethylene glycol) (PEG) having molecular weight 2000 (or lower) has been used as a good biphasic solvent for regioselective reaction of n-butyl vinyl ether 

Uses of some additives are recommended. Addition of Ag2C03 cleanly suppresses double bond isomerization in products. In addition, Ag salts accelerate reactions, possibly by removing halide ions strongly attached to Pd from a coordination sphere to generate a cationic Pd catalyst, making the insertion easier. Thallium salts also accelerate reactions, and suppress the double bond isomerization. A favorable effect of some alkali halides, sueh as LiCl and KBr, on the reaction is known [25]. 

Larock found that the reaetion of 2-iodo -methylbiphenyl (34) with acrylate provided two products 35 and 36 in equal amounts using cesium pivalate as a base. Of course, 35 is an expected produet [27]. Also the reaction of 37 afforded the mixture of 35 and 36. Gallagher also diseovered a similar migration using 3-bromo-4-phenylpyridine (38) and acrylate to afford 39 and 40 [28]. Although the mechanism of the migration process to form the crossover produets is not clear, certainly a reversible 1,4-Pd shift of arylpalladium intermediates 41 and 43 via the palladacycle 42 is occurring. 

Reetz reported that a highly active ligandless Pd eatalyst for HR of aryl bromides can be generated by combining Pd(OAc)2 or PdCl2(PhCN)2 with N,N-dimethylglycine (DMG), and TON 106700 was obtained with this catalyst in the reaction of bromobenzene with styrene, although the reaction was slow [29,30]. 

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