Palladium-catalyzed hydrogenation reaction

Substituted-2-phenylbenzo[. ]furans were able to undergo a palladium-catalyzed hydrogenation reaction to give their corresponding 2,3-dihydrobenzo[ ]furans, but the yields are quite low (Scheme 51) <2002T4261>. 

As previously mentioned, the tin(ll) chloride reduction used by medicinal chemistry was replaced by a palladium catalyzed hydrogenation reaction. The amine 6 could be isolated as a crystalline solid or salt, but it was more efficient to use the ethyl acetate solution of 6 directly in the next stage. The activation of the acid 9 was studied using thionyl chloride, oxalyl chloride, and... 

Thus, in contrast to benzothiepins, dibenzo compounds can be synthesized by direct acid-catalyzed elimination of water from hydroxy derivatives, or of amines from amino derivatives, at elevated temperatures due to their thermal stability. As in the case of benzothiepins, dibenzo derivatives can also be prepared by base-catalyzed elimination from the corresponding halo derivatives however, the yields are somewhat lower compared to the acid-catalyzed reactions. As a special case, an aziridine derivative was deaminated by palladium-catalyzed hydrogenation to afford the corresponding dibenzothiepin.69... 

Catalysis and Synthesis in the Laboratory. Research on the practical applications of catalysis was not matched in the laboratory. We began a study of metal and non-metal catalyzed reactions early in our sonochemistry program. Our first project was to develop a convenient method of hydrogenating a wide range of olefins. We chose formic acid as our hydrogen source and found it to be effective. For example, with continuous irradiation, palladium catalyzed hydrogenations of olefins are complete in one hour(44). 

The 2,3-substituted indols are formed via a palladium-catalyzed coupling reaction of aryl halide, o-alkenylphenyl isocyanide, and amine (Equation (122)).481 Oxidative addition of an aryl halide, insertion of both the isonitrile and alkene moieties of o-alkenylphenyl isocyanide, and 1,3-hydrogen migration may form a 7r-allylpalladium species, which is then attacked by an amine to afford an indol. 

It was concluded that the high selectivity observed in the hydrogenation experiments using 26 b is explained by the relatively strong coordination of the alkyne to the palladium center, which only allows for the presence of small amounts of alkene complexes. Only the latter are responsible for the observed minor amounts of ( )-alkene, which was shown to be a secondary reaction product formed by a subsequent palladium-catalyzed, hydrogen-assisted isomerization reaction. Since no n-octane was detected in the reaction mixture, only a tiny... 

Secondary phosphine oxides are known to be excellent ligands in palladium-catalyzed coupling reactions and platinum-catalyzed nitrile hydrolysis. A series of chiral enantiopure secondary phosphine oxides 49 and 50 has been prepared and studied in the iridium-catalyzed enantioselective hydrogenation of imines [48] and in the rhodium- and iridium-catalyzed hydrogenation functionalized olefins [86]. Especially in benzyl substituted imine-hydrogenation, 49a ranks among the best ligands available in terms of ex. 

Another variation of the palladium-catalyzed carbonylation reaction occurs when hydrogen is added rather than an alcohol or a primary or secondary amine. This variation leads to aldehyde formation the hydrogen reduces the acylpalladium intermediate to aldehyde and metal hydride (76). A basic tertiary amine is also added as in the ester-forming reaction to neutralize the hydrogen halide formed in the dissociation of the hydride ... 

In Figure 2 are compared the activities of various palladium catalysts for the reductions carried out with carbon monoxide (9) (in these experiments, the hydrogen necessary for the reduction is obtained by the palladium catalyzing the reaction CO -f- H2O — CO2 -f- H2). It can be... 

The palladium-catalyzed hydrogenation of this molecule at room temperature has been investigated both in the gas phase, using a flow-system (90), and in the liquid phase using a solvent (57). The products of the gas phase reaction were cis-2-butene, 52% trans-2- mtene, 7% 1-butene, 40% and w-butane, 1%. Isomerization of the reactant was also observed, 2-butyne being produced to the extend of about 10% of the total olefin yield, together with traces of 1-butyne and 1,3-butadiene. 

A variety of palladium-catalyzed organic reactions involve the oxidative addition process. A typical example is seen in the catalytic arylation and alkenylation of olefins (eq (60)) [85]. Aryl- and alkenylpalladium(ll) complexes (9) formed by oxidative addition undergo olefin insertion into the palladium-carbon bond to give an alkylpal-ladium species (10), which provides arylated and alkenylated olefins via p-hydrogen elimination. The hydridopalladium species 11 thus generated is reduced to a Pd(0) species upon its interaction with a base and carries the sequence of reactions... 

Palladium catalyzed hydrogenation of 3/3-acetoxy- or 3/3-hydroxy-A- -steroids affords 5-10% of the corresponding 3-desoxy steroids. The hydrogenation can be catalyzed by 70% perchloric acid. 3/3-Acetoxy-5a-steroids are resistant to hydrogenolysis hence the reaction probably involves partial isomerization of the A -double bond to the Apposition, followed by hydrogenolysis of the allylic group.40... 

Palladium-catalyzed hydrogenation in the presence of a base, such as ammonia gas, sodium or ammonium hydroxide, is the preferred method for the removal of chloro substituents reaction with red phosphorus and hydriodic acid has been found to be ineffective.58,75,56 Thus, dechlorination of 5,8-dichloropyrido[2,3-tf]pyridazine by hydrogenation gives the parent compound 3 in 69% yield.58... 

The palladium catalyzed hydrogenation of compound I was carefully studied for the effect of pH, solvent, catalyst load, temperature, and concentration. Standard reaction conditions described in the experimental section were used for all screening reactions. 

Platinum and palladium are expensive metals, so the accidental finding by Paul Sabatier 1854-1941) that nickel, a much cheaper metal, can catalyze hydrogenation reactions made hydrogenation a feasible large-scale industrial process. The conversion of plant oils to margarine is one such hydrogenation reaction. Sabatier was born in France and was a professor at the University of Toulouse. He shared the 1912 Nobel Prize in chemistry with Victor Grignard (p. 468). 

---