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Trends in Heterocyclic Chemistry   Volumes    Volume 2 
New free and grafted, more stable NADH models for chemo and enantioselective reductions
G. Dupas, J. Duflos, J. Bourguignon, G. Queguiner
Pages: 127 - 141
Number of pages: 15
Trends in Heterocyclic Chemistry
Volume 2 

Copyright © 1991 Research Trends. All rights reserved

NADH models bearing a 1,4-dihydronicotinamide moiety have been widely studied in three directions : I) Design of an insoluble support where the dihydronicotinamide reagent was grafted with a view of faciliting the use of the reagent. The optimal conditions for using such models were defined, and the scope and limitations of these reagents were examined. II) Synthesis of stable reagents towards secondary reactions. In this field, an original method for the construction of a pyridine ring substituted with suitable groups was used leading to numerous precursors of annelated NADH models. Several of these reagents show high reactivity: they allow the reduction of previously reported non-reducible substrates, some of them being precursors of target molecules. Other models could be used in the presence of hard Lewis acid allowing the first efficient reductions of non actived ketones. Ill) Chiral models were developed bearing chiral aminoalcohols as chiral auxiliaries. The alcoholic function plays an important role in the rigidification of the chiral auxiliary which favors the stereodifferenciation of the two faces of the dihydropyridine. By using this methodology it was possible to perform high enantioselective transfers of hydrogen to prochiral substrates. In some cases it was possible to obtain, with high enantiomeric excess, one major enantiomer, or the other, by using the same reagent under different proper experimental conditions. Grafted chiral models also allow the obtention of high enantiomeric excesses.
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