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

摘要

Organometallic disaccharides containing a chromium carbene speacer habe 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-#alpha#-D-galacto-hecodiald-1,5-ose,activated by TiCl_4,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.