CYCLIC ACETALS OF 4,1',6'-TRICHLORO-4,1',6'-TRIDEOXY-GALACTO-SUCROSE AND THEIR CONVERSION INTO METHYL-ETHER DERIVATIVES

The acid-catalysed reaction of 4,1′,6′-trichloro-4,1′,6′-trideoxy-galacto-sucrose (1) with 5.5 equiv. of 2-methoxypropene in N,N-dimethylformamide followed by acetylation gave 3′,4′-di-O-acetyl-4,1′,6′-trichloro-4,1′,6′-trideoxy-2,3-O-isopropylidene-6-O-(1-methoxy-1-methylethyl)-galacto-sucrose (2, 2%), 6,3′,4′-tri-O-acetyl-4,1′,6′-trichloro-4,1′,6′-trideoxy-2,3-O-isopropylidene-galacto-sucrose (3, 31%), 3′,4′-di-O-acetyl-4,1′,6′-trichloro-4,1′,6′-trideoxy-2,3-O-isopropylidene-galacto-sucrose (4, 38%), 3′-O-acetyl-4,1′,6′-trichloro-4,1′,6′-trideoxy-2,3-O-isopropylidene-galacto-sucrose (5, 13%), and 2,3′,4′-tri-O-acetyl-4,1′,6′-trichloro-4,1′,6′-trideoxy-galacto-sucrose (6, 13%). Methylation of 4 followed by removal of the protecting groups gave 4,1′,6′-trichloro-4,1′,6′-trideoxy-6-O-methyl-galacto-sucrose (8). 4,1′,6′-Trichloro-4,1′,6′-trideoxy-3-O-methyl-galacto-sucrose (11) was synthesised from 6 by preferential tert-butyldiphenylsilylation of HO-6 followed by methylation and removal of the protecting groups. Likewise, 4,1′,6′-trichloro-4,1′,6′-trideoxy-4′-O-methyl-galacto-sucrose (14) was synthesised from 5. Treatment of 3 with aqueous acetic acid followed by methylation and removal of the protecting groups afforded 4,1′,6′-trichloro-4,1′,6′-trideoxy-2,3-di-O-methyl-galacto-sucrose (17). © 1990.