Palladium as a Catalyst

For trisubstituted olefins, the nucleophile attacks predominantly at the less substituted end of the allyl moiety, e.g. to afford a 78 22 mixture of 13 and 14 (equation 7). Both the oxidative addition of palladium(O) and the subsequent nucleophilic attack occur with inversion of configuration to give the product of net retention7. The synthesis of the sex pheromone 15 of the Monarch butterfly has been accomplished by using bis[bis(l,2-diphenylphosphinoethane)]palladium as a catalyst as outlined in equation 87. A substitution of an allyl sulfone 16 by a stabilized carbon nucleophile, such as an alkynyl or vinyl system, proceeds regioselectively in the presence of a Lewis acid (equation 9)8. The... 

The use of palladium as a catalyst is common in the development and synthesis of active pharmaceutical ingredients (APIs). Palladium is an expensive metal and has no known biological function. Therefore, there is a need to recover spent palladium, which is driven both by cost and by government regulations requiring residual palladium in APIs to be <5 ppm (1). Thus, much research has been conducted with the aim of heterogenizing active palladium that can then be removed via simple filtration and hopefully reused without significant loss of activity. 

The first examples of the use of palladium as a catalyst for carbon-carbon coupling reactions were reported almost thirty years ago [14], and over recent decades a massive effort has been devoted to the extension of the scope of palladium-catalyzed reactions. Organic and organometallic chemists have received extensive input from palladium-coordination chemistry in the task of understanding the mechanisms behind these efficient synthetic procedures [14]. 

The activity of palladium as a catalyst in the determination of hydrogen by combustion is unaffected by the presence of traces of arsine.3... 

Colloidal palladium or platinum supported on chelate resin beads were employed for the stereoselective hydrogenation of olefins 86). Colloidal palladium supported on iminodiacetic acid type chelate resin beads was prepared by refluxing the palladium chloride and the chelate resin beads in methanol-water. Using the resin-supported colloidal palladium as a catalyst, cyclopentadiene is hydrogenated to cyclopentene with 97.1% selectivity at 100 % conversion of cyclopentadiene under 1 atm of hydrogen in methanol at 30 °C. Finely dispersed metal particles ranging from 1 to 6 nm in diameter are the active species in the catalyst. 

The simplest case is that of the ATb-methylstrychninium ion with palladium as a catalyst, the acetate undergoes normal allylic hydrogenolysis to give XC as the main product, together with small quantities... 

The ethylidene moiety in these alkaloids does not hydrogenate readily in alcohols if platinum is used, but goes well in the presence of acetic acid, hydrogen usually coming in such a way as to end up with the ethyl in the isoajmaline configuration (20, 23, 63). However, with palladium as a catalyst in alcohol, sarpagine has apparently given only the alternative dihydro product (16, 62). 

The first reported example of DKR of an amine derives from Reetz et al. in which they employed palladium as a catalyst for the racemization of a methylbenzylamine 1 in the presence of CAL B [37]. The reaction was carried out in pyridine, with ethyl acetate as the acyl donor, at a temperature of 50 55 °C. In order to achieve total conversion to the N acylated product, it was necessary to leave the reaction for 5 days giving the (R) amide in 64% yield and 99% ee. Kim and coworkers extended this approach by employing the in situ reduction of the corresponding oxime 56 to the... 

Palladium, as a catalyst with a high selectivity of action, was chosen for investigation. Its properties have been studied in the hydrogenation of unsaturated compounds of various types [63, 64]. However, the selectivity of palladium in the hydrogenation of dienes has not so far been used in their identification. 

Recently, Hada et al. [74] have reported a theoretical study on the reaction mechanism and regioselectivity of silastannation of acethylene with a palladium catalyst. Experimentally, terminal acetylenes react with silylstan-nanes to give highly regio- and stereoselective l-silyl-2-stannylalkenes with tetrakis(triphenylphosphine)palladium as a catalyst [75]. The products are always cis adducts tin adds to the internal position as follows ... 

Table 3.13. Perfluoroalkylation of Vinylic Halides with te-trakis (triphenylphosphine) palladium as a catalyst [73]...

In 1990 Fukuyama and co-workers reported the mild and selective reduction of thioesters to aldehydes with triethylsilane using palladium as a catalyst (Scheme 19).[52),[53] jjjg reaction can be used with aromatic (29) and aliphatic (30) thioesters and tolerates chiral centers very well as applied to the intermediate 31 in the synthesis of (+)-neothramcycin. 

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