Halogenation reactions of derivatives of d-glucose and sucrose

Abstract

Treatment of methyl 4,6- O-benzylidene-α- d-glucopyranoside ( 1) with triphenylphosphine-carbon tetrachloride-pyridine (reagent A) gave methyl 4,6- O-benzylidene-2-chloro-2-deoxy-α- d-mannopyranoside ( 2). When reagent A was used in excess, a further elimination reaction occurred to give methyl 4,6- O-benzylidene-2-chloro- ( 6, 60%) and -3-chloro-2,3-dideoxy-α- d- erythro-hex-2-enopyranoside ( 7, 16%). Treatment of 1 with triphenylphosphine-carbon tetrabromide-pyridine (reagent B) caused little or no elimination, and 47% of methyl 4,6- O-benzylidene-2-bromo-2-deoxy-α- d-mannopyranoside ( 14) was obtained. On treatment with reagent A, methyl α- d-glucopyranoside ( 16) gave exclusively methyl 2,4,6-trichloro-2,3,4,6-tetradeoxy-α- d- erythro-hex-2-enopyranoside ( 17), and methyl 4,6- O-benzylidene-β- d-glucopyranoside ( 19) gave methyl 4,6- O-benzylidene-3-chloro-3-deoxy-β- d-allopyranoside ( 20, 70%). However, with reagent B, 19 gave methyl 4,6- O-benzylidene-3-bromo-3-deoxy-β- d-glucopyranoside ( 23, 66%), probably by way of double inversion of configuration at C-3. Likewise, with reagent A, methyl β- d-glucopyranoside ( 25) gave methyl 2,4,6-trichloro- ( 26) and 3,4,6-trichloro-2,3,4,6-tetradeoxy-β- d- threo-hex-2-enopyranoside ( 27), and 4,6- O-isopropylidenesucrose ( 28) gave mainly 3-chloro-3-deoxy-4,6- O-isopropylidene-α- d-allopyranosyl 1,4,6-trichloro-1,4,6-trideoxy-β- d- lyxo-hexulofuranoside ( 29) together with 3-chloro-3-deoxy-4,6- O-isopropylidene-α- d-allopyranosyl 1,4,6-trichloro-1,4,6-trideoxy-β- d-fructofuranoside ( 30). The assignment of structure to 29 is tentative.