Synthesis of an intensely sweet chlorodeoxysucrose: Mechanism of 4′-chlorination of sucrose by sulphuryl chloride

A new synthesis of 6-O-acylsucroses and of mixed 6,6'-di-O-acylsucroses

Various 6-O-acylsucroses were synthesized in good yields from unprotected sucrose in N,N-dimethylformamide and the appropriate 3-acylthiazolidine-2-thiones 6 or 3-acyl-5-methyl-1,3,4-thiadiazole-2(3H)-thiones 7. A selective ionization of the free sugar by sodium hydride or triethylamine, followed by acylation with 6, gave 2-O-acylsucroses which were subjected in situ to intramolecular isomerizations using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or an aqueous solution of triethylamine to yield 6-O-acylsucroses. The later were otherwise obtained directly when sucrose was acylated with 6 or 7 in the presence of DBU. Moreover, mixed 6,6'-di-O-acylsucroses were readily obtained from 6'-monoacylates by using a Mitsunobu reaction without involving the concomitant formation of the 3',4'-epoxide.

Halogenation reactions of derivatives of D-glucose and sucrose

Treatment of methyl 4,6-O-benzylidene-alpha-D-glucopyranoside (1) with triphenylphophine-carbon tetrachloride-pyridine (reagent A) gave methyl 4,6-O-benzylidene-2-chloro-2-deoxy-alpha-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-alpha-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-alpha-D-mannopyranoside (14) was obtained. On treatment with reagent A, methyl alpha-D-glucopyranoside (16) gave exclusively methyl 2,4,6-trichloro- 2,3,4,6-tetradeoxy-alpha-D-erythro-hex-2-enopyranoside (17), and methyl 4,6-O-benzylidene-beta-D-glucopyranoside (19) gave methyl 4,6-O-benzylidene-3-chloro-3-deoxy-beta-D-allopyranoside (20, 70%). However, with reagent B, 19 gave methyl 4,6-O-benzylidene-3-bromo-3-deoxy-beta-D-glucopyranoside (23, 66%), probably by way of double inversion of configuration at C-3. Likewise, with reagent A, methyl beta-D-glucopyranoside (25) gave methyl 2,4,6-trichloro- (26) and3,4,6-trichloro-2,3,4,-6-tetradeoxy- beta-D-threo-hex-2-enopyranoside (27), and 4,6-O-isopropylidenesucrose (28) gave mainly 3-chloro-3-deoxy-4,6-O-isopropylidene-alpha-D-allopyranosyl 1,4,6-trichloro-1,4,6-trideoxy-beta-D-lyxo-hexulofuranoside (29) together with 3-chloro-3-deoxy-4,6-O-isopropylidene-alpha-D-allopyranosyl 1,4,6-trichloro-1,4,6-trideoxy-beta-D-fructofuranoside (30). The assignment of structure to 29 is tentative.