Carbohydrate Based and Related Ketones

Fructose-derived ketone 39 is readily available, and is a highly general and enantio-selective catalyst for the epoxidation of trans- and trisubstituted olefins. Its utilization in synthesis has been reported by other researchers [70]. For example, recently Corey and coworkers reported that (R)-2,3-dihydroxy-2,3-dihydrosqualene (47) was enantio- 

A precise mechanistic understanding of the origin of the enantioselectivity with ketone 57 awaits further investigation. The scope for the substrate for the epoxidation of 57 is expected to be further expanded in the future. 

The reacting carbonyl and the stereogenic centers are usually contained in a cyclic stracture for most of the ketones discussed above. Several ketones in which the carbonyl and the chiral moiety are combined by a non-cycUc structure have also been studied for epoxidation. 

The author is grateful to Christopher Burke, Zackary Crane, David Goeddel, Dr. Jiang Long, and other research group members for their assistance during the preparation of this manuscript. 

For recent reviews on asymmetric epoxidation of electron-deficient olefins, see (a) M.J. Porter, J. Skidmore Chem. Commun. 2000, 1215-1225  

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Scheme 3.7 Selected examples of carbohydrate-based and related ketones.

The antitumour alkaloids of the pancratistatin and narciclasine classes have been the subject of several synthetic efforts this year. The L-mannonolactone derivative 51 is the starting material for a synthesis of narciclasine analogue 55 and two related compounds. The key transformations are elaboration of the carbohydrate adduct 53, derived by base-catalysed coupling of 51 with the anion derived from benzamide 52 to the cyclohexanone derivative 54. This involves selective removal of the C5,C6 isopropylidene group, oxidative cleavage of the C5,C6 bond and an intramolecular aldol reaction involving the C5-derived aldehyde and the benzylic ketone enolate (Scheme 10). ... 

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