Total Synthesis of 4-O-Methyl-DL-lyxose and 4-Deoxy-DL-ribose. Further Evidence of the Stereoselective Hydroxylation of Double Bonds by Osmic Acid

Abstract

Methyl 4-O-methyl-α-DL-lyxopyranoside (6) and methyl 4-deoxy-β-DL-erythro-pentopyranoside (3) were obtained in excellent yield as the sole isolable products of the reaction of osmic acid in pyridine on cis-2,5-dimethoxy-5,6-dihydro-2H-pyran (2) and 2-methoxy-5,6-dihydro-2H-pyran (1), respectively. Hydrolysis of 6 and 3 gave respectively 4-O-methyl-DL-lyxose (9) and 4-deoxy- DL-ribose (8).The attack on the double bond of 1 and 2 occurs nearly completely if not exclusively from the unhindered side, remote from the substituent. These results indicate that 1 must be predominantly in the conformation in which the C-2 alkoxy group is quasi axial.