Intramolecular Reactions of Carbohydrate Triflates

Article abstract of DOI:10.1021/jo00034a030

Each of the four possible methyl 2,6-dideoxy-β-D-hexopyranosides (3-6) was treated with an equivalent amount of triflic anhydride in the presence of 2,6-di-tert-butyl-4-methylpyridine (7).The ribo isomer 3 produced both the 3-O-triflyl (8, 15percent) and the 4-O-triflyl (9, 73percent) derivatives while the lyxo isomer 4 gave only the 3-O-triflyl compound (11, 84percent).Upon heating, the triflate 8 lost the elements of triflic acid to form methyl 2,3,6-tri-deoxy-β-D-glycero-hexopyranosid-4-ulose (23, 72percent), while 9 experienced ring contraction involving the pyranoid ring oxygento form methyl 3,5-anhydro-2,6-dideoxy-β-D-xylo-hexofuranoside (20, 54percent).Compound 11 produced methyl 3-C-aldehydo-2,5-dideoxy-β-D-threo-pentofuranoside (13, 65percent).Upon reaction with triflic anhydride, methyl 2,6-dideoxy-β-D-arabino- and -xylo-hexopyranosides (5 and 6, respectively) generated hydroxy triflates which were not isolated due to their further reaction below room temperature.Compound 5 produced aldehyde 13 (54percent) while reaction of 6 gave methyl 3,4-anhydro-2,6-dideoxy-β-D-lyxo- and -ribo-hexopyranosides <15 (48percent) and 16 (24percent), repectively>.The mechanisms for these reactions are discussed and the reactivity of the hydroxy triflates is compared to that of related carbohydrate derivatives.