A NEW SYNTHESIS OF 2-C-METHYL-D-RIBONO-1,4-LACTONE AND THE C-9 C-13 FRAGMENT OF METHYNOLIDE

The synthesis of the glucosaccharino lactone, 2-C-methyl-D-ribono-1,4- lactone 7 from 2,3-O-isopropylidene-D-glyceraldehyde 1 is reported. La ctone 7 was transformed into (2R,3R)-2,3-dihydroxy-2-methylpentanoic a cid 18 (the C-9/C-13 fragment of Methynolid) by two new procedures whi ch improve on existing alternatives: conversion of the epoxide derivat ive 9 to the episulfide 14 and subsequent reduction; and reductive ope ning of the 5-bromo derivative of 3-O-isopropylidene-2-C-methyl-D-ribo no-1,4-lactone and subsequent hydrogenation.