C-glycoside synthesis II: Henkt condensations of 4,6-O-alkylidene pyranoses with a 1,3-proton transfer catalyst- a roote to blocked aminomethyl-c-glycosides

Article abstract of DOI:10.1016/S0040-4020(01)86545-5

In the presence of a novel 1,3-proton transfer catalyst (2-hydroxypyridine (2-HP)/ 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)/molecular sieves), 4,6-Obenzylidene-D-glucopyranose (1),4,6-O-isopropylidene-D-mannose (12), and 4,6-O-isopropyridene-D-glucose (16) undergo Henry condensations with nitromethane in THF to give acetal protected nitromethyl C-glycopyranosides (2, 13, and 17, respectively), which were characterized as their O-acetyl derivatives (5, 15, and 18, respectively). The Henry product from 4,6-O-benzyridene-D glucopyranose could be reduced, with retention of the 4,6-O-benzylidene protecting group, by a specially prepared form of elemental iron in aqueous tetrahydrofuran under CO₂ to aminomethyl-C-glycopyranoside (16), characterized as N-acetyl, peracetyl, and N-Cbz derivatives (7, 8, 9, 10), and converted with diazonium salt to a triazene derivative (II). Nitroalkenes are only mechanistic intermediates in our condensations with nitromethane, but they undergo Michael additions with a second mole of nitromethane to give novel 5,7-O-alkylidene-1,2-deoxy-1 nitro-2-nitromethyl-D-heptitols (3 and 14) as side-products.