Hydrogenation stereoselective

Table 1 gives a broad summary of the reactions of the corrunon classes of reducing agents, In the following sections some typical examples of synthetically useful reductions (in the educt order given on the table) together with some more sophisticated methods of stereoselective hydrogenations will be discussed. 

An example of a stereoselective hydrogenation in ionic liquids was recently successfully demonstrated by Drie en-H6lscher et al. On the basis of investigations into the biphasic water/n-heptane system [51], the ruthenium-catalyzed hydrogenation of sorbic acid to cis-3-hexenoic acid in the [BMIM][PFg]/MTBE system was studied [52], as shown in Scheme 5.2-8. 

Scheme 5.2-8 Stereoselective hydrogenation of sorbic acid in the [BMIM][PFg]/MTBE biphasic...

R. Noyori and T. Ohkuma, Asymmetric Catalysis by Architectural and Functional Molecular Engineering Practical Chemo- and Stereoselective Hydrogenation of Ketones , Angew. Chem. Int. Ed. Engl, 2001, 40, 40. 

Redox-type reactions show by far the worst performance in meeting the golden atom economical threshold. Three reductions meet this criterion with (AE)min values of 1 hydrogenation of olefins using the Lindlar catalyst (1952), Noyori stereoselective hydrogenation reaction (1985), and Zincke disulphide cleavage reaction (1911) whereas, oxidations... 

Stereoselective hydrogenation of Pd Lindlar cataly.st Insect sex Agrochemicals... 

The event, oxidative addition of a Ni(0) species upon dienes and aldehydes activated by coordination with Lewis acids to provide oxanickellacycles 45, has proven to take place quite generally, and many variations making the best use of the intermediate 45 have been developed. The key issue of the reactions discussed in Sect. 3 is a regioselective and stereoselective hydrogen delivery... 

Changing catalyst support from carbon to calcium carbonate leads to dramatic improvement of the cis/tran ratio from 6 1 to 18 1, that is the cis selectivity increases from 85.7% to 94.7%. The reason for better selectivity on CaC03 supported catalyst is attributed to its lower surface area leading to lower hydrogenation activity, but more selective to the desired product. The successful commercialization of the new route for sertraline synthesis demonstrates that for a stereoselective hydrogenation reaction, improve product selectivity can be achieved by proper selection of catalyst support. 

Noyori, R. and Okhuma, T. (2001) Asymmetric catalysis by architectural and functional molecular engineering practical chemo- and stereoselective hydrogenation of ketones. Angewandte Chemie-International Edition, 40 (1), 40-73. 

Phenylselenation of the position a to the ketone carbonyl in compound 125 followed by oxidative elimination gave the enone 126 in moderate yield, with a selenide as an intermediate. Compound 127, obtained by further manipulation of 126, was stereoselectively hydrogenated over PtC>2 to give the corresponding alcohol 128 (Scheme 18) <20020L1611>. 

There is considerable interest in amino derivatives of chroman and hydrogen bromide has been found to promote a stereoselective hydrogenation of an a-hydroxyoxime enabling the 5,5-aminochromanol 53 to be obtained in over 30% yield from chroman-4-one on a multi-kilo scale (Scheme 31) <00TL8021>. 

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