Rhodium catalysis epoxide reactions

Although C—C connecting reactions are discussed elsewhere in Comprehensive Organic Synthesis , it may be mentioned that epoxides react regioselectively with carbon monoxide under rhodium catalysis (equation 51) and benzyl bromides undergo carbonylation and subsequent lactonization under the influence of a Pd" catalyst (equation 52). The [2 -( 2] cycioaddition of ketenes to carbonyl compounds, catalyzed by Lewis acids, is a familiar route to 3-lactones (equation 53). 

Molecular hydrogen can reduce cyclic peroxo complexes, for example Reaction 30 (111), and Sheldon and Van Doom (33) had envisaged epoxide production via a similar process, Reaction 31. A mechanism based on such reactivity (with subsequent epoxide isomerization) is a possibility for our catalysis using H2/02, although Reaction 31 did not occur under mild conditions (33). Isolation of a related peroxometallocyclic rhodium complex, (Ph3As)2Rh[02C2(CN)4] + (92), allows for a testing of Reaction 31 at a Rh center. 

The present interest in asymmetric catalysis was demonstrated by awarding Nobel prizes to three winners W. S. Knowles (USA) for elaboration of rhodium complex catalysts effective in asymmetric synthesis of anti-Parkinson medicine, R. Noyori (Japan) for elaboration of a new catalytic system based on chiral ruthenium-phosphine complex catalysts that are very effective in hydrogenation reactions, and B. Sharpless (USA) for elaboration of epoxidation and other reactions under the action of chiral titanium complexes. 

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