From Diol Groups on Cyclic Carbohydrates

From Diol Groups on Cyclic Carbohydrates.—Acid-catalysed acetonation of D-glycero-n-galacto-h Xo Q yielded only 1,2 3,4 6,7-tri-O-isopropylidene- 

6- (major) and 2,3 6,7-di-0-isopropylidene-j3-D- /ycero-L-/wfl/i/io-hepto-furanose (minor), respectively. Unsaturated acetal derivatives have been prepared by heating methyl D-hexopyranosides with acrolein, crotonaldehyde, and cinnamaldehyde, etc., in the presence of toluene-p-sulphonic acid methyl a-and /S-D-glucopyranoside and methyl a-D-galactopyranoside afforded 4,6-acetals, whereas methyl a-D-mannopyranoside gave 2,3 4,6-diacetals. Methyl 4,6-0-benzylidene-2,3-0-methylene-a-D-mannopyranoside was formed when the parent c/j-2,3-diol was treated with dichloromethane in a two-phase system in the presence of a phase-transfer catalyst.  

Acetalation of l,6-anhydro-l(6)-thio-D-glucitol with acetone, formaldehyde, or benzaldehyde furnished 2,3 4,5-diacetals whose structures, after desulphurization, were established by m.s. On partial hydrolysis of the 2,3 4,5-di-0-isopropylidene derivative, one of the isopropylidene groups was removed and the other migrated to 0-3 and -4 to give the monoacetal (53). 

Methyl 2,3-0-benzylidene-4-0-methyl-a-L-rhamnopyranoside (54) was converted by butyl-lithium at — 30 °C into methyl 2,6-dideoxy-4-0-methyl- 

Jedlinski, J. Maslinska-Solich, and A. Dworak, Uniw. Adama Michiewicza Poznaniu, 

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