Condensation of D-mannosaldehyde derivatives with ethyl diazoacetate. An easy and stereoselective chain elongation methodology for carbohydrates: Application to new syntheses for KDO and 2-deoxy-beta-KDO.

(3R and 3S) beta-Hydroxy-alpha-diazocarbonyl compounds 4(100%, 3:2), 9 (35%, 100:0), 14 (74%, 7:2) and 18 (100%. 100:0), prepared from 2,3,4.5.6-penta-O-acetyl- (3), penta-O-benzyl- (8), 2.3:5,6-di-O-isopropylidene-4-O-(tert-bulyldimethylsilyl)- (13), and 2.3:5,6-di-0-isopropylidene-4-0-acetyl-D-mannosaldehyde (17), respectively, were acetylated, and the resulting beta-ncetoxy-alpha-diazocarbonpl compounds treated with rhodium diacetate to give the corresponding-alpha-enolesters,6 (100%). 11 (35%), 16(100%)and 20 (100%),which are potentially alpha-ketoesiers. Molecularmechanics calculations were used in order to justify the stereoselectivity observed in the initial addition process. The problematic removal of the protecting groups from the alpha-keto esters is discussed. Finally, hydrazinolysis of the cc-enol acetates (to quench the labile resulting a-keto ester as the corresponding and less reactive hydrazines), mild oxidation to the corresponding alpha-diazoesters, deprotection, and final oxidation of the diazo group with m-chloroperhenzoic acid, gave KDO in good yield. Intermediate products were used in the completely stereoselective synthesis of 2-deoxy-beta-KDO, a potent inhibitor for CMP-KDO synthetase. (C) 1997 Published by Elsevier Science Ltd.