Stereochemically-complex Oxygen Heterocycles

Methods for the preparation of optically active compounds have been reviewed. Still and his co-workers recently developed the hydroboration of acyclic 1,4-dienes as a method for the controlled creation of stereocentres. Two groups have now exploited this method in a short synthesis of the Prelog-Djerassi lactone (111). The key step in both routes is the hydroboration-oxidation of (109) to (110) that is highly stereoselective with respect to three of the four stereocentres of (110). 

Several of the anthracycline antibiotics are highly effective against a wide variety of tumours, but possess a toxicity that severely limits dosage. In consequence considerable efforts have been directed towards modification of structure, and in one case lowering of toxicity has been achieved by replacing the carbohydrate moiety L-daunosamine (115) by its C-4 epimer L-acosamine (116). A chiral synthesis of both these compounds has now been reported. The key step is an intramolecular nitrone-olefin cycloaddition [(112) - (113) and (114) in a ratio of 82 18] in which the chiral side-chain exerts considerable asymmetric induction. The major isomer (113) could be converted to either (115) or (116) by conventional means. 

The utilization of sugars as a source of cheap, chiral starting materials continues to flourish. Thus, D-glucose serves as the starting material in syntheses of tirandamycic acid (117), tylonolide (118), and carbomycin B (119) and leucomycin A3 (120).  

Masamune and his collaborators have contributed much to the development of the stereoselective aldol condensation. Through the use of chiral boron 

Finally, a fitting memorial to the late R. B. Woodward is provided by the publication of three papers describing the total synthesis of erythromycin 

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