Conjugated dienes palladium-catalyzed

After that, studies on the palladium-catalyzed reactions of conjugated dienes attracted little attention. They have only been reexamined since the late 1960 s. The scope of the reaction of butadiene catalyzed by palladium complexes has gradually been established. The catalysis by palladium is different from those of other transition metals. Although palladium is located below nickel in the periodic table, the catalytic... 

There are two main types of reactions of conjugated dienes catalyzed by palladium complexes. The first type is the linear dimerization to form 1,3,7-octatriene (16) in the absence of a nucleophile ... 

A mild aerobic palladium-catalyzed 1,4-diacetoxylation of conjugated dienes has been developed and is based on a multistep electron transfer46. The hydroquinone produced in each cycle of the palladium-catalyzed oxidation is reoxidized by air or molecular oxygen. The latter reoxidation requires a metal macrocycle as catalyst. In the aerobic process there are no side products formed except water, and the stoichiometry of the reaction is given in equation 19. Thus 1,3-cyclohexadiene is oxidized by molecular oxygen to diacetate 39 with the aid of the triple catalytic system Pd(II)—BQ—MLm where MLm is a metal macrocyclic complex such as cobalt tetraphenylporphyrin (Co(TPP)), cobalt salophen (Co(Salophen) or iron phthalocyanine (Fe(Pc)). The principle of this biomimetic aerobic oxidation is outlined in Scheme 8. 

If the side chain with the nucleophile is situated in the 1-position of the conjugated diene, a palladium-catalyzed spirocyclization occurs. In this case stereoselective oxa-spirocyclizations were obtained from the diene alcohols 59 and 60 (equation 23 -25)58. The reaction worked well for the formation of a tetrahydrofuran and tetrahydropyran in the spirocyclization. In the absence of chloride ions 59 gave high yields of the acetoxy oxaspirocyclic compound 61 via a 1,4-anti addition across the diene (equation 23). In the presence of stoichiometric amounts of LiCl a 1,4-syn oxychlorination took place and allylic chloride 62 was obtained (equation 24). Under chloride-free conditions, cyclohep-tadiene alcohol 60 afforded oxaspirocyclic acetate 63 (equation 25). 

PALLADIUM-CATALYZED SYNTHESIS OF CONJUGATED DIENES (5Z.7E)-5,7-HEXADECADIENE... 

Other conjugated cyclic dienes undergo a similar palladium-catalyzed stereoselective 1,4-diacetoxylation.578... 

Palladium acetate triarylphosphine complexes catalyze the addition of vinylic groups from vinylic halides to olefinic compounds in the presence of amines. Conjugated dienes are major products from 0,/3-unsaturated acids, esters, or nitriles while unactivated olefinic compounds react best in the presence of secondary amines where allylic amines are major products. The reactions are usually regio- and stereospecific. The synthetic utility of the reaction is illustrated with a wide variety of examples. 

Early findings by Heck and co-workers [56] have shown that the palladium-catalyzed coupling of aromatic halides, non-conjugated 1,3 dienes and secondary amines gives the corresponding arylallylated amines. A representative example is given in Scheme 8.20. 

This palladium-catalyzed three-component coupling reaction leading to the formation of aryl-substituted allylic amines was recently adapted to solid-phase synthesis (Scheme 8.23). Amines were chosen to attach to a solid support (Rink resin) in this three-component coupling process and were reacted with a variety of aryl halides and linear or cyclic non-conjugated dienes, the reaction being carried out at 100 °C for two days in the presence of palladium acetate and diisopropylethyl-amine. A wide variety of aryl-substituted allylic amines were then obtained after cleavage from the solid support by trifluoroacetic acid [60],... 

Palladium(II)-catalyzed couplings of vinyl(phenyl)iodonium salts with mono-substituted alkenes to give conjugated dienes have also been explored132. Such reactions proceed readily at room temperature and generally occur with retention of configuration in the vinyliodonium component and rnam-stereoselectivity in the olefinic substrate (equations 253-256). 

Conjugated (E, )-dienes can also be synthesized from ( -1 -alkenyl-1, 3,2-bcnzo-dioxaboroles by palladium catalyzed reactions (Eq. 88) 142145> and (Eq. 89)146) in high regio- and stereospecificity. 

Three-component additions, comprising two conjugated diene molecules and a nucleophile, can be catalyzed by palladium salts, such as palladium acetate. The major products are 1-substituted 2,7-octadienes, along with minor amounts of 3-substituted 1,7-octadienes (equation 65). Water, alcohols, phenols, carboxylic acids, and amines are some of the nucleophiles that have been used in this reaction. 

Catalytic hydroboration is a new methodology of great synthetic potential. The reaction is usually carried out with catecholborane in the presence of rhodium, palladium, iridium and ruthenium compounds.2 In contrast to olefins, very little is known on catalytic hydroboration of conjugated dienes and enynes. Our earlier studies on the uncatalyzed monohydroboration of conjugated dienes,6 reports on the hydroboration of 1-decene with catecholborane catalyzed by lanthanide iodides,7 and monohydroboration of 1,3-enynes in the presence of palladium compounds,8 prompted us to search for other transition metal catalysts for monohydroboration of conjugated dienes and enynes 9 10... 

---