Fluorination by anchimeric assistance of a diallylamino group: application to the synthesis of some methyl aminofluoropentofuranosides

The Synthesis and Glycoside Formation of Polyfluorinated Carbohydrates

“…With the β-anomer of methyl 2,3-anhydro-D-lyxofuranoside β-635, obtained in five steps from D-xylose as discussed in Scheme 92, the epoxide opening with dimethyl amine was less selective (Scheme 135B), giving a 75:25 ratio of inseparable 958 and 959. 450 Mesylation of this mixture led to another inseparable mixture of 960 and 961. These converged to the same aziridinium ion β-954 upon treatment with Et 4 NHF 2 , which underwent regioselective opening with fluoride, with some fluorination at C-5 as well, to give β-955 and 962 in modest yields.…”

“…295 It was also demonstrated that oxime resin aminolysis was possible, leading to the C-terminal fluoroglycopeptide 951. 448 449,450 Methyl 2,3-anhydro-β-D-lyxofuranoside α-635, whose synthesis in five steps from D-xylose was discussed in Scheme 96, was converted to the N,N-dimethyl aminosugar derivative 952 with full regioselectivity. 450 Following hydroxyl group mesylation, treatment with Et 3 N•2HF initially gave rise to formation of aziridinium species α-954, whereupon nucleophilic substitution with fluoride took place with moderate regioselectivity to give α-955 and 956.…”

“…448 449,450 Methyl 2,3-anhydro-β-D-lyxofuranoside α-635, whose synthesis in five steps from D-xylose was discussed in Scheme 96, was converted to the N,N-dimethyl aminosugar derivative 952 with full regioselectivity. 450 Following hydroxyl group mesylation, treatment with Et 3 N•2HF initially gave rise to formation of aziridinium species α-954, whereupon nucleophilic substitution with fluoride took place with moderate regioselectivity to give α-955 and 956. Fluorine substitution at the 5position, reported to be difficult, only proceeded in low yield with the more reactive tetraethylammonium hydrogen difluoride to yield 957.…”

“…Fluorine substitution at the 5position, reported to be difficult, only proceeded in low yield with the more reactive tetraethylammonium hydrogen difluoride to yield 957. 450 Direct treatment of 953 with Et 4 NHF 2 only returned a complex reaction mixture.…”

“…These converged to the same aziridinium ion β-954 upon treatment with Et 4 NHF 2 , which underwent regioselective opening with fluoride, with some fluorination at C-5 as well, to give β-955 and 962 in modest yields. 450 With the 2,3-anhydroribofuranoside substrate β-721 (Scheme 135C), obtained in five steps from the commercially available 717 as discussed in Scheme 102, regioselective epoxide opening with ammonia followed by protection as the diallyl amine led to 963. Mesylation of the alcohols to 964 was followed by fluorination, which now proceeded first through azetidinium Subsequent fluorination proceeded then via an aziridinium intermediate, giving both the F-2 and F-3 products 966 and 967.…”