By Palladium Catalysts

Alkenylboronic acids, alkenyl boronate esters, and alkenylboranes can be coupled with alkenyl halides by palladium catalysts to give dienes.223... 

The second characteristic reaction catalyzed by palladium catalysts is cocyclization of butadiene with the C=0 bonds of aldehydes and the C=N bonds of isocyanates and Schiff bases to form six-membered heterocyclic compounds (19) with two vinyl groups, as expressed by the following general scheme ... 

The most characteristic reaction of butadiene catalyzed by palladium catalysts is the dimerization with incorporation of various nucleophiles [Eq. (11)]. The main product of this telomerization reaction is the 8-substituted 1,6-octadiene, 17. Also, 3-substituted 1,7-octadiene, 18, is formed as a minor product. So far, the following nucleophiles are known to react with butadiene to form corresponding telomers water, carboxylic acids, primary and secondary alcohols, phenols, ammonia, primary and secondary amines, enamines, active methylene compounds activated by two electron-attracting groups, and nitroalkanes. Some of these nucleophiles are known to react oxidatively with simple olefins in the presence of Pd2+ salts. Carbon monoxide and hydrosilanes also take part in the telomerization. The telomerization reactions are surveyed based on the classification by the nucleophiles. 

Palladium-catalyzed olefin arylation reactions ( Heck coupling ) have been successfully employed for the generation of C-C bonds in organic synthesis for decades [174-177]. Arylhalides and olefins are coupled by palladium catalysts (typically with phosphine co-ligands) in the presence of base, such as a tri-alkylamine. 

Borylation of 1-alkenyl iodides and triflates with HBpin was catalyzed by palladium catalyst in the presence of Et3N (Equation (61)).330 Platinum(0)-AsPPh3 complexes catalyzed the borylation of allyl chlorides (Equation (62)).331,332... 

The C-allylation to ortho-carborane is accelerated by palladium catalysts. 

It is noteworthy that Takeda and coworkers (Ref. 154) recently proposed allyl isopropenyl dicarbonate made from isopropenyl chloroformate and sodium allyl carbonate as a convenient reagent for the preparation of allyl esters of carboxylic acids. Allyl isopropenyl dicarbonate reacts with carboxylic acids in the presence of DMAP under mild neutral conditions to give allyl esters in high yields. Allyl esters which could be deprotected by palladium catalysts are especially useful in the case of unstable compounds under acid or basic conditions, for example O-glycopeptides, penicillin derivatives, etc. 

Metathesis of Si-Si bonds is promoted by palladium catalysts presumably through bis(organosilyl)palladium(II) complexes. Though metathesis reaction of linear disilanes results only in disproportionation of the disilanes [88],use of cyclic disilane provides a useful method for the synthesis of macrocyclic or polymeric organosilicon compounds having newly formed Si-Si bonds. 

Peptide cleavage. In the presence of BF3-etherate the Cb group of methionine-containing peptides can be removed quantitatively by hydrogenolysis catalyzed by palladium catalyst.21... 

Nickel complexes also exhibit high catalytic activity toward the hydrosiiyiation of conjugated dienes under mild conditions. The reaction usually occurs by 1,4-addition, but the regio- and stereoselectivity is low compared with that achieved by palladium catalysts. 

Table 12.3 Carbonylation of aryl iodides catalysed by palladium catalyst (1).

Figure 19 Alternating ethylene-CO polymerization by palladium catalysts...

The earlier methods of reducing acidp or esters to alcohols Involved the use of metallic sodium with anhydrous alcohols also, an acid derivative, such as the acid chloride, could be reduced by direct hydrogenation to an aldehyde by palladium catalysts. The direct reduction, using molecular hydrogen at high pressure, involves 2 moles of hydrogen per mole of acid reduced, as shown in the following reaction ... 

Figure 3. Representative structure of a highly branched random copolymer of ethylene and methyl acrylate produced by palladium catalysts.

As a typical example, a catalytic cycle for ether formation from aryl halide and alkali metal alkoxide catalyzed by palladium catalyst is shown in Scheme 1.6. 

But the regiospecific oxidation of olefinic compounds by palladium catalysts is enjoying increasing importance as a step in the multistep syntheses of complex organic compounds such as pharmaceuticals, pesticides, and fragrances. The carbonyl compounds are reactive intermediates in such syntheses. 

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