The Variation of Reaction Conditions

The success of asymmetric hydrogenation as a route to amino acid derivatives does not find more general applicability. To appreciate why this is so, an analysis of the various factors involved is required. The limitations will only be overcome when a full appreciation of mechanism and of the source of stereoselectivity has been assimilated. 

The simplest case is that of a 5-ring chelate based on 1,2-Z w(diphenylphosphino)ethane. Inorganic stereochemists have long appreciated the chiral conformations adopted by 2,3-diaminobutane derivatives, but it was not until 1977 that Fryzuk and Bosnich applied this knowledge to phosphine chemistry. The synthesis of chiraphos and its cationic rhodium complex (7) was most fruitful, and optical yields of nearly 

CYPHOS, (10). Chiral 1,2-6/5(diphenylphosphino)-ethane units may be derived by resolution procedures as in the case of norphos, 

The basic framework of diop, which is a C2 chiral 1,4-to(diphenylphosphino)butane derivative, is subject to wide variation. The 

A final example of the chelating substrate principle is given by reduction of enol phosphates, an interesting feature being the high (and not 

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It was shown that the variation of reaction conditions (mole ratio of starting substrates, catalyst concentration, temperature, conversion, etc) enables the process to be performed with high selectivity, with respect to target dienes and polyenes of required length and desired stereo-content. 

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