Best Synthetic Methods Reduction

The stereocontrolled reductive amiaation of cyclic ketones such as 15 has been a continuing challenge. Shawn Cabral of Pfizer, Inc. in Groton, CT has reported Tetrahedron Lett. 2007, 48, 7134) complementary reagent combinations, leading selectively to either 16 or 17. 

To control catalytic hydrogenation, it is often desirable to control the supply. John S. McMurray of the University of Texas M. D. Anderson Cancer Center in Houston has shown J. Org. Chem. 2007, 72, 6599) that EtjSiH is a convenient Hj source. 

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Best Synthetic Methods Enantioselective Oxidation and Reduction... 

R. L. Augustine (1965). Catalytic Hydrogenation Techniques and Application in Organic Synthesis. London Arnold M. Hudlicky (1984). Reduction in Organic Chemistry. Chichester Horwood P. N. Rylander (1985). Hydrogenation methods , in Best Synthetic Methods. Eds A. R. Katritzky, O. Meth-Cohn and C. V. Rees. London Academic Press. 

During the course of developing a synthetic method for the central eight-membered ring of Taxol, the preparation of alcohol 5 was required.7 Thus, the Luche reduction of ketone 4 proceeded smoothly to give 5 with undefined stereochemistry. This reaction best demonstrates the enhanced regioselectivity obtained in the Luche process. In addition to... 

Reactions of Amides Because amides are the most stable acid derivatives, they are not easily converted to other derivatives by nucleophilic acyl substitution. From a synthetic standpoint, their most important reaction is the reduction to amines, which is one of the best methods for synthesizing amines. Amides are hydrolyzed by strong acid or strong base. Just as nitriles can be hydrolyzed to amides, amides can be dehydrated to nitriles. 

Reduction of nitro compounds to amines is an essential step in what is probably the most important synthetic route in aromatic chemistry. Nitro compounds are readily prepared by direct nitration when a mixture of o- and p-isomers is obtained, it can generally be separated to yield the pure isomers. The primary aromatic amines obtained by the reduction of these nitro compounds are readily converted into diazonium salts the diazonium group, in turn, can be replaced by a large number of other groups (Sec. 23.11). In most cases this sequence is th best method of introducing these other groups into the aromatic ring. In addition, diazonium salts can be used to prepare the extremely important class of compounds, the azo dyes. 

Use of imines as synthetic intermediates has been limited to mainly two processes reduction to amines, and as precursors to azaallyl anions for reaction with a variety of electrophiles (equation 36). The former transformation can often provide the best access to highly substituted amines and the latter represents one of the highest yield methods for carbon-carbon bond formation a to the carbonyl group of an aldehyde or ketone. Thus, the following sections will deal not only with imines but also with the properties and chemical reactions of the derived anions. Several reviews are available (in addition to those that cover both enamine and imine anion chemistry) as the result of recently uncovered methods for asymmetric induction through reactions of the anions. > ... 

Synthetic ways to dihydropyridines can be classified into ring-forming processes and ring transformations, liie first general approach is best represented by the versatile Hantzsch synthesis. This method conveniently affords 1,4-dihydro- or 3,4-dihydro-, but not 1,2-dihydro-pyridines. The second approach may be illustrated by partial reduction of pyridines or pyridinium salts and nucleophilic addition of organometallic reagents to pyridines and pyridinium salts leading to 1,2- or l,4-dihydropyridines . 

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