Methyl 3,4-0-benzylidene 2,3-dibromo-2,3-dideoxy

Methyl 2,4 3,5-di-0-benzylidene-D-ribonate, R-128 Methyl 2,4 3,5-di-0-benzylidene-D-xylonate, X-9 Methyl 2,4-dibromo-2,4-dideoxy-L-erythronate, D-541 Methyl 2,4-dibromo-2,4-dideoxy-D-threonate, D-541 Methyl 2,4-dibromo-2,4-dideoxy-L-threonate, D-541 Methyl 2,3-dideoxy-5,6-0-isopropylidene-D-er ytAra-hexonate, T-167 Methyl 2,3-dideoxy-5,6-0-isopropylidene-4-0-tosyl-D-erj i/iro-hexonate, T-167... 

For the synthesis of the D-C portion, two different concepts were followed either by modification of laminaribiose (166) [89] or by a stereospecific P, 1 ->3-glycosylation [20]. Laminaran is isolated from seaweeds or from Poria cocos Wolf, degraded by selective acetolysis, and the lower oligomers separated by preparative HPLC [90]. Following acetylation, the heptaacetyl laminaribiosyl bromide is prepared and transformed into the disaccharide glycal 167 by the classical approach in 93 % yield. The 2-deoxy-2-iodo-a-glycoside is formed by application of the NIS procedure after deprotection and subsequent 4,6-0-benzylidenation, the precursor 168 for the radical formation of the 6,6 -dibromo-6,6 -dideoxy derivative is at hand. This compound may be further reduced to methyl-3-0-(P-D-chinovosyl)-a-D-olivoside (169). 

The isolated alkenes undergo normal additions, frequently with high regio- and stereoselectivity. For example, methyl 4,6-0-benzylidene-2,3-dideoxy-a-D-eryi/2w-hex-2-enopyranoside 87 gives the 2,3-dibromo-D-a(fro-adduct 88 on treatment with bromine, and the 2-0-acetyl-3-bromo-3-deoxy adduct 89 is obtained when treated with acetyl hypobromite (O Scheme 46), indicating that the reactive bromonium ion intermediate is formed on the lower (a) face of the ring [78]. 

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-... 

Me glycoside, 4,6-benzylidene Methyl 4,6-0-benzylidene-2,3-dibromo-2,3-dideoxy-a-D-altropyranoside [20853-45-6]... 

Methyl 3,4-0 - R )-benzylidene-2-deoxy-2-iodo-a-D-altropyranoside, D-246 Methyl 3,4-0-(5 )-benzylidene-2-deoxy-2-iodo-a-D-altropyranoside, D-246 Methyl 4,6-0-benzylidene-2-deoxy-2-iodo-a-D-altropyranoside, D-246 Methyl 4,6-0-benzylidene-2-deoxy-2-iodo-p-D-altropyranoside, D-246 Methyl 4,6-0-benzylidene-2-deoxy-2-iodo-a-D-idopyranoside, D-261 Methyl 4,6-O-benzylidene-2,3-dibromo-2,3-dideoxy-a-D-altropyran0side, D-525... 

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