Organotransition metal modified sugars Part 21. Synthesis of organometallic disaccharides bearing two monosaccharide moieties linked by a chromium carbene spacer

Organometallic disaccharides containing a chromium carbene spacer have been synthesized from tetramethylammonium acetyl(pentacarbonyl)chromate(-I) (1) in a two-step protocol. An acylation/alcoholysis sequence applying di(isop ropylidene)-protected glucose, mannose, galactose and fructose afforded O-g lycoside methylcarbene complexes 6-9 in 29-84% yield. Upon reaction with 1, 2:3,4-di-O-isopropylidene-alpha -D-galacto-hexodiald-1,5-ose, activated by TiCl4, they undergo a trans-selective aldol condensation to give a 53-89% y ield of chromium vinylcarbene O,C-disaccharides (10-13) which are promising candidates for subsequent benzannulation, cyclopropanation, Diels-Alder- a nd Michael addition reactions. (C) 2001 Elsevier Science B.V. All rights re served.