Altropyranoside 4.6- 0-benzylidene-2-deoxy

C. B. Barlow and R. D. Guthrie, Periodate oxidation of methyl amino-4,6-0-benzylidene-deoxy-a-D-altropyranosides, Carbohydr. Res., 13 (1970) 199-202. 

C21H20BrNO7S Methyl 4,6-0-benzylidene-2-0-(p-bromophenylsulfonyl)-3-cyano-3-deoxy-a-D-altropyranoside BZSALT 30 455... 

The reaction of methyl 2-azido-4,6-0-benzylidene-2-deoxy-a-D-altropyranoside (46) with 39 in refluxing 1,1,2,2-tetrachloroethane afforded a product which was formulated83(b) as methyl 2-azido-3,4-0-benzylidene-6-chloro-2,6-dideoxy-a-D-altropyranoside (47) the n.m.r. spectrum indicated that the product was a mixture of two diastereoisomers which differed in the configuration of the carbon atom of the benzylidene acetal. A possible mechanism for the formation of 47 is outlined. 

The reaction of 39 with methyl 4,6-0-benzylidene-2-deoxy-2-iodo-a-D-altropyranoside (48) gave a complex mixture of products, from which methyl 4,6-0-benzylidene-2,3-dideoxy-a-D-eryf/iro-hex-2-eno-pyranoside (50) could be isolated. The formation of 50 was ex-plained83(b) by attack by chloride ion on the iodine atom in intermediate 49, followed by elimination of the substituent at C-3. Compound 50 itself reacts with reagent 39, and, therefore, prolonged reaction times led to extensive decomposition. 

A novel method of opening of oxiranes involves the use of (chlo-romethylene)dimethyliminium chloride (39) [see Section II,2c p. 250], monochlorodeoxy or dichlorodideoxy derivatives are obtained, depending upon the reaction conditions employed.83 Thus, methyl 2,3-anhydro-4,6-0-benzylidene-a-D-allopyranoside (110) reacts with 39 in 1,1,2,2-tetrachloroethane at room temperature to give, upon hydrolysis of the primary adduct 111 with an aqueous solution of sodium hydrogen carbonate, methyl 4,6-0-benzylidene-2-chloro-2-deoxy-3-0-formyl-a-D-altropyranoside (112). If a solution of 39 and 110 in 1,1,2,2-tetrachloroethane is heated at reflux temperature, methyl 3,4-0-benzylidene-2,6-dichloro-2,6-dideoxy-o -D-altropyrano-side (113) is obtained in high yield the n.m.r. spectrum of 113, like that of 47 (see Section II, 2c p. 250), showed the presence of two diastereoisomers which differed in the configuration of the benzyl-idene-acetal carbon atom. 

As might be expected, the nitrous acid deamination of methyl 2-amino-4,6-0-benzylidene-2-deoxy-a-D-altropyranoside (10) hydrochloride leads45,46 uniquely to methyl 2,3-anhydro-4,6-0-benzylidene-a-D-allopyranoside (11). The benzylidene group does not play an... 

The deamination of methyl 3-amino-3-deoxy-/3-D-altropyranoside was studied in 1934, but the products were not fully characterized.14411 The syrupy product was converted into a methylated derivative that had an elemental analysis corresponding to that calculated for a methyl tetramethylhexoside. The conditions used for methyl-ation would have opened an epoxide ring. Methyl 2,3-anhydro-4,6-0-benzylidene-a-D-mannopyranoside precipitated quantitatively from solution when the corresponding 3-amino-3-deoxyaltroside derivative was deaminated in aqueous medium.145 Epoxide formation was likewise reported to be quantitative in the deamination of the analogous 2-amino-2-deoxyaltroside.83 145 On deamination, 4-amino-l,6-anhydro-4-deoxy-/3-D-mannopyranose also gave an epoxide, namely, 1,6 2,3-dianhydro-/3-D-talopyranose, in unspecified yield.146... 

When benzyl 3-azido-3-deoxy-4,6-0-benzylidene-a-D-altropyranoside (compound I) is treated with diethylaminosulfur trifluoride (DAST), three products are obtained II, III, and IV. Compound II results from... 

A number of epimino sugars have been prepared by the action of lithium aluminum hydride in tetrahydrofuran on vicinal benzamido sulfonates oriented in the trans relationship. Treated in this way, methyl 3 - benzamido -4,6-0 -benzylidene - 3 - deoxy -2-0- (methylsul-fonyl)-a -D-altropyranoside afforded - methyl 4,6-O-benzylidene-... 

Fig. 11. A planar, extended W coupling pathway (heavy bonds) in methyl V-2, 4 -dinitrophenyl-3-amino-4,6-0-benzylidene-3-deoxy-2-0-methyl-a-D-altropyranoside, which results in a long-range coupling constant of 5J16 0.5 Hz.

B. Coxon and R. C. Reynolds, Boat conformations. Synthesis, NMR spectroscopy, and molecular dynamics of methyl 4,6-0-benzylidene-3-deoxy-3-phthalimido-a-D-altropyranoside derivatives, Carbohydr. Res., 331 (2001) 461 67. 

Methyl 4,6-0-benzylidene-3-deoxy-3-phthalimido-a-D-altropyranoside derivatives 246... 

A re-investigation of the reaction (conducted with methyllithium free from halide ion) which afforded the methylated derivative (1, R = Me, R = H), indicated that it proceeded by way of methyl 4,6-0-benzylidene-2-deoxy-2-C-methyl-a-D-altropyranoside (2, R= Me, R = H), because this compound [prepared by opening the corresponding 2,3-anhydroalloside with (methylsulfinyl)methyl carbanion, to give methyl 4,6-0-benzylidene-2-deoxy-2-C-[(methylsulfinyl) methyl]-a-D-altropyranoside (2, R = MeSOCH2, R = H), followed by reduction with Raney nickel], on treatment with methyllithium, also gave the C-methyl compound (1, R = Me, R = H).5... 

Other additions to the double bond of compounds in this series have not been studied extensively, but reports now indicate that several such additions can be accomplished efficiently. Nitryl iodide is, however, not added92 to the double bond of compound 45, but bromination in methanol, in the presence of barium carbonate, gives crystalline methyl 4,6-0-benzylidene-2,3-dibromo-2,3-dideoxy-a-D-altropyranoside in 70% yield.93 On treatment with potassium tert-butoxide in refluxing xylene, this compound undergoes elimination of the elements of hydrogen bromide to give methyl 4,6-O-benzylidene-2-bromo-2,3-dideoxy-a-D-t/ireo-hex-3-enopyranoside (46, R = Br) in 90% yield. Likewise, compound 45 reacts with acetyl hypobromite to give methyl 3-0-acetyl-4,6-0-benzylidene-2-bromo-2-deoxy-a-D-glu-... 

A more satisfactory synthesis of compounds of this type has been achieved by use of sulfonic esters. Thus, methyl 4,6-0-benzylidene-3-O - (methyl sulfonyl) - 2 - S - phenyl - 2 - thio - a - D - altropyranoside gave methyl 4,6-0-benzylidene-3-deoxy-2-S-phenyl-2-thio-a-D-ert/ hro-... 

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