Enamides catalytic hydrogenation

The catalytic hydrogenation of enamide 34 in the presence of 0.5-1 mol% of (/ )-BINAP complex in a 5 1 mixture of ethanol and dichloromethane under 1-4 atm of hydrogen affords 35 with quantitative yield and higher than 99.5% ee. The (fi)-isomer is not reduced under similar reduction conditions. This approach provides a route to a number of alkaloid compounds (Scheme 6-19).47... 

Enantioselective catalytic hydrogenation. The ruthenium(II) complexes of (R)- and (S)-l, bearing a chiral BINAP ligand, catalyze asymmetric hydrogenation of N-acyl-l-alkylidenetetrahydroisoquinolines to give (1R)- or (lS)-tetrahydroiso-quinolines in 95-100% ee.1 Thus the (Z)-enamide (2), prepared by acylation of 3,4-dihydropapaverine, is hydrogenated in the presence of (R)-l to (1R)-tetrahydroisoquinolines (3). The enantiomeric (lS)-3 is obtained on use of (S)-l as catalyst. 

Only a few reactions have been studied with N-allenylsulfenimides. Despite the presence of a sulfur function in allene 281, van Vranken and co-workers carried out its heterogeneous catalytic hydrogenation (Eq. 8.39) [148], The reaction occurs only at the terminal C=C bond, providing the Z-configuration enamide 296 in 70% yield. 

Fig. 8 Optimal arrangement of the enamide substituents for catalytic hydrogenation...

Heterogeneous catalytic hydrogenation was initiated using enamide substrate 88. Various catalysts were employed and the effects of pressure and solvent variation were investigated (Scheme 43). The results obtained at atmospheric pressure are summarized in Table 7. 

By using the p-methoxy-substituted enamide (192), Ninomiya et al. (54) succeeded in a simple synthesis of alloyohimbone (196) via the unconjugated lactam 194, which has an enol ether structure. Lithium aluminum hydride reduction of the lactam 194, followed by hydrolysis with hydrochloric acid and subsequent catalytic hydrogenation over platinum dioxide, yielded alloyohimbone (196) stereoselectively in an overall yield of 59% from harmalane (54) this was the most convenient synthesis of alloyohimbone (196) so far reported (Scheme 75). 

Oxidative photocyclization of the enamide 273 gave the same aporphine (271) in 15% yield this was then converted to ( )-nuciferine by LAH reduction of the carbamate, followed by catalytic hydrogenation of ring C (136) (Scheme 100). 

L-dopa, used in the treatment of Parkinson s disease, is best prepared by asymmetric catalytic hydrogenation (15) of the enamide [6]. The hydrogenation, performed with a soluble rhodium catalyst modified with the... 

Quantitative yields of the adducts (109) are obtained by low temperature, -20 to 40°C, irradiation of the enamine carbaldehyde (110) with the alkenes (111). The enamide (112) also undergoes photoaddition of acrylonitrile. The adduct from this, on catalytic hydrogenation, provides a synthetic route to the carboxamides (113). ... 

Recent work by several research groups has shown that supercritical fluids can be superior to other solvents for several chemical processes. For example, DeSimone has demonstrated the ability of supercritical CO2 to replace Freons in the free radical polymerization of fluorinatkl acrylate monomers. 34) Noyori has shown that significant rate enhancements can be achieved in supercritical carbon dioxide relative to other solvents for the homogeneous catalytic hydrogenation of carbon dioxide to either formic acid or its derivatives in the presence of triethylamine or triethylamine/methanol respectively, (equation 1). (55-57) As discussed below, we have recently demonstrated that improved enantioselectivities can be achieved in supercritical carbon dioxide for the catalytic asymmetric hydrogenation of several enamides. 5 8)... 

In addition, as discussed above, oxidation reactions and reactions which use CO2 as a reagent as well as a solvent are worth investigating. Examples of both are discussed below. Finally, electrophilic processes may be advantageously transferred to supercritical CO2, as demonstrated by the improved isomerization of C4-C12 paraffins catalyzed by aluminum bromide. 2,44) Below, we describe three catalytic reactions which appear promising by these criteria asymmetric catalytic hydrogenation of enamides, ruthenium-catalyzed two-phase oxidation of cyclohexene, and the catalytic copolymerization of CO2 with epoxides. 

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