Intramolecular C-arylation of 2,3,5-tri-O-benzyl- and 2,3,5-tri-O-(3-methylbenzyl)-pentofuranose derivatives.
Upon treatment with tin(IV) chloride, 1-O-acetyl-2,3,5-tri-O-benzyl- and 1-O-acetyl-2,3,5-tri-O-(3-methylbenzyl)pentofuranose (D-ribo, L-arabino) undergo intramolecular Friedel-Crafts alkylation of the aromatic substituent at O-2 to give unusual internal C-glycosyl compounds (isochroman derivatives) in high yield. The final products are also partially debenzylated at O-3 or O-5 (up to 25%) under these conditions. By contrast, the corresponding methyl glycosides are poor substrates for the intramolecular C-arylation reaction, as methyl 2,3,5-tri-O-(3-methylbenzyl)-beta-D-ribofuranoside was found to give preponderantly methyl 3,5-di-O-(3-methylbenzyl)-alpha-D-ribofuranoside (11) (49%), and the C-arylation product in 30% yield only in the presence of the same Lewis acid. The competitive formation of 11 is thought to be due to the anomerization of the substrate leading to a tin(IV) complex coordinated with O-1 and O-2, which promoted the cleavage of the benzyl group at O-2. These reactions provide a novel and efficient C-arylation method and suggest a new approach to selectively protected D-ribofuranose derivatives. Evidence for the uncommon C-arylated structure of the new products was gained from their 1H- and 13C(APT)-n.m.r. spectra.
Department of Chemistry, University Center at Binghamton, State University of New York 13901.
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Martin
D001593:Benzyl Compounds; D006027:Glycosides / Q000138:chemical synthesis*; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D013329:Structure-Activity Relationship
D001593:Benzyl Compounds; D006027:Glycosides; D007202:Indicators and Reagents