Stereoselective cyclizations of unsaturated esters derived from 2,3-O-isopropylidene-D-ribose

Abstract

We describe the preparation of several α,β-unsaturated esters by means of Wittig reactions with 5-O-dimethyl-t-butylsiloxy-2,3-O-isopropylidene-D-ribose, and methods for the stereoselective cyclization of these compounds to produce 1-β-substituted 1-deoxyribose derivatives. One of these derivatives (1b; R = SiMe₂Bu^t) was converted into a protected form of dihydroshowdomycin (8). Reaction of the die-ester, methyl (6S,7S,8R)-8,9-dihydroxy-6,7-O-isopropylidene-3-methyl (2E,4Z)-non-2,4-dienoate (1c; R = H) with benzeneselenenyl chloride produced 2-hydroxymethyl-3,4-O-isopropylidene-5-phenylselenenyl-6-[3-methoxycarbonyl-(E)prop-2-en-2-yl]pyran (7), for which an X-ray structure was obtained. Crystals were monoclinic, space group P2₁, Z= 2, with a= 10.591(8), b= 10.730(8), c= 9.832(9)Å, β= 109.2(1)°. 1 513 Independent reflections above background were measured on a diffractometer; the structure was refined to R 0.074.