Stereoselectivity catalytic

The rhodium cyclopentadienyl complex [T75-C5(CH3)5RhCl2]2, in the presence of base at 50 atm H2, also effects stereoselective catalytic hydrogenation of benzenes. Substrates with unprotected —OH or —C02H groups were not effectively hydrogenated, but aryl ethers, esters, and ketones and N,iV -dimethylaniline were all reduced, some-... 

Stereoselective catalytic cyclizations are now known, with excellent enantioselectivities observed (Equation (117)).106... 

Minerals with stereoselective, catalytic and ion-sieve properties have been discussed. 

Stereoselective catalytic oxidation of Aryl methyl sulfides. 300... 

STEREOSELECTIVE CATALYTIC OXIDATION OF ARYL METHYL SULFIDES... 

The intramolecular cyclopropanation of appropriate y,(5-unsaturated a-diazoketones following a stereoselective catalytic reduction of the cyclopropyl ketone group provides a useful approach in diterpenoid synthesis. Some examples of the use of the cyclopropanation-reductive cleavage approach in synthesis are shown in equations 67 and 68l0f103. 

Metal-n-allyl complexes are important in a number of stereoselective catalytic reactions and are therefore attractive for computational chemists (see also Chapter 13, Section 13.2). An empirical force field study based on the MM2 parameterization scheme aimed at predicting stereoselective nickel(0)-catalyzed cycloadditions was recently conducted 56. As in a similar study 57, where a force field for the structure optimization of palladium-allyl systems was developed, dummy atoms were needed to define the structural model. Based on the assumptions required to model a catalytic process, the results obtained have to be interpreted with caution. 

The key step in the synthesis is the stereoselective catalytic hydrogenation of the acety-... 

Monzani E, Linati L, Casella L et al (1998) Synthesis, characterization and stereoselective catalytic oxidations of chelated deuterohaemin-glycyl-L-histidine complexes. Inorg Chim Acta 273 339-345... 

New, preferentially stereoselective, catalytic reagents will produce enantio-merically pure products, the specific chemical activity of which reduces adverse effects when applied in agriculture or medicine. Biocatalysis will continue to play an important role here. 

The key step in the synthesis of 2-deoxycrustecdysone from the corresponding 20-oxo steroid is the stereoselective catalytic hydrogenation of the a,(3-unsaturated lactone to afford a 2 3 mixture of 8- and "y-lactones, respectively. This crude product was converted into the thermodynamically more stable y-lactone by treatment with aqueous NaOH. a,p-Unsaturated aldehydes and ketones are hydrogenated to produce allylic alcohols in high regioselectivity using hydridoiridium phosphine complexes, such as [Ir(PEt2Ph)4]4. 5 ... 

There must be enantiopure chiral information in the stereoselective step. This can be achieved either by using covalent attachment to one of the substrates (stereoselective auxiliary-based methods) or by creating a complex that is cleaved after the stereoselective elementary step under the reaction conditions and reused for the next molecule (stereoselective catalytic methods). Substrate control is observed when the substrates themselves are chiral,... 

Reactions of this type use palladium in stoichiometric or catalytic amounts. Earlier results are compiled in several reviews1-7 78,79. This section focuses on stereoselective catalytic oxycarborative addition reactions. 

The conversions of lycorine and caranine derivatives to a- and lycoranes take advantage of the stereoselective catalytic reduction of the 3—3a double bond. In these transformations, the configurations of the asymmetric centers at Cub and Cug are the same as in the parent alkaloids. Because of the trans relationship between the Ci-hydroxyl and the Ciiij-hydrogen, dehydration of the alkaloids and their a- and /3-dihydro derivatives occurs readily with phosphorus oxychloride and pyridine to give 1,11b unsaturation. Catalytic reduction of these olefins... 

Commercial hexythiazox is a racemic mixture of the two trans enantiomers Scheme 26.2.2 shows the main synthetic pathways [11, 17, 19]. Starting from 4-chloro propiophenone the key intermediate erythro amino alcohol may be obtained by stereoselective catalytic reduction of the corresponding hydroxy imi-noketone or by sodium borohydride reduction of the aminoketones obtained via Gabriel synthesis. Different routes lead from this aminoalcohol to the trans-thiazolidinone system the basis of all routes is activation of the hydroxy group, e.g., in form of the sulfonate and a ring forming reaction with carbon disulfide or carbonyl sulfide. The final acylation of the NH group with cyclohexyl isocyanate leads to hexythiazox. 

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