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Stereochemical aspects of the hydrogenolysis of derivatives of terpenoid and steroidal allylic alcohols

Posted on 23. February, 2018.

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Hydrogenolysis involves the replacement of a C–X bond by a C–H bond in a reaction in which X is typically a halogen, oxygen, sulfur, selenium or nitrogen or, less commonly, carbon. In some cases it may be difficult to distinguish between hydrogenolysis and the protonolysis of an organometallic intermediate.

Although hydrogenolysis is most commonly encountered in the removal of protecting groups such as the benzyl group in synthesis, it occurs in many other situations. There are a number of structural features that promote the hydrogenolysis of a C–X bond involving the presence of an adjacent alkene, aryl or carbonyl group. The regiochemistry and stereochemistry of the reaction depend on the reagent, the conditions and the environment of the C–X bond. These features have been explored in many studies, particularly in the chemistry of the terpenoids and steroids where the cyclic structures enable the stereochemical consequences of the reactions to be more easily evaluated. The hydrogenolysis reactions of terpenoid and steroidal allylic and homoallylic alcohols and their derivatives, in which there is the potential for the participation of the double bond, form the subject of this review.

In the course of the chemical degradation of natural products, hydrogenolysis reactions have provided useful evidence for the relationships between functional groups. In subsequent work, these reactions have played an important role in the transformation of one natural product into another, particularly in the preparation of less readily available compounds from more abundant and more highly oxygenated sources. Useful stereochemical information concerning these reactions has been obtained during these studies. Reducing agents can be divided into heterogeneous and homogeneous catalytic systems, radical reagents, hydride reagents and ionising (‘dissolving’) metal systems. Hydrogenolysis reactions will be discussed in the context of these reagents.

Read the full review article, free of charge in Journal of Chemical Research, Volume 42, Number 1, January 2018, pp. 1-6.


Keywords: hydrogenolysis, allylic alcohol, terpenoid, steroid, stereochemistry

Author: James R. Hanson
Department of Chemistry, University of Sussex, Brighton, Sussex BN1 9QJ, UK