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(isopropylidene)-protected glucose, mannose, galactose and fructose afforded O-glycoside methylcarbene complexes 6–9 in 29–84% yield. Upon reaction with 1,2:3,4-di-O-isopropylidene-α-d-galacto-hexodiald-1,5-ose, activated by TiCl4, they undergo a trans-selective aldol condensation to give a 53–89% yield of chromium vinylcarbene O,C-disaccharides (10–13) which are promising candidates for subsequent benzannulation, cyclopropanation, Diels–Alder- and Michael addition reactions.