An olefin metathesis route for the preparation of (1→6)-linked C-disaccharide glycals.: A convergent and flexible approach to C-saccharide synthesis

A convergent route to a variety of C-1-disaccharide glycals based on the olefin metathesis reaction of enol ethers and alkenes is described. The DCC-mediated coupling reaction of a variety of pentose enitols (la-c) with a number of C-5- and C-6-monosaccharide carboxylic acids (2a-e) gave the corresponding esters 3a-1 in good yield. Methylenation of these compounds was followed by ring-closing metathesis, mediated by the Schrock molybdenum catalyst 8 in warm toluene, to provide the target C-disaccharide glycals 5a-1. The formed enol ether double bond in 5a was then transformed, via standard manipulations, into a variety of C-disaccharide derivatives 21-25.