Add time:08/23/2019         Source:sciencedirect.com

The acetonation of lactose with 2-methoxypropene afforded 4,6-O-isopropylidene lactose (2) and a diacetal which, after acetylation, gave an α,β-anomeric mixture of 1, 2,6,3'-tetra-O-acetyl-3,2':4',6'-di-O-isopropylidene lactose (4). Acetonation of benzyl b-lactoside afforded the mixed acetals benzyl 6,6'-di-O-(methoxydimethyt)methyl (6), 6'-O-(methoxydimethyl)methyl-(7) and 6-O-(methoxydimethyl) methyl-β -lactoside (8), the cyclic acetal benzyl 4',6'-O-isopropylidene.-β-lactoside (9) and a diacetal which, after acetylation gave benzyl 2, 6, 3'-tri-O-acetyl-3,2':4',6'-di-O-isopropylidene-β-lactoside (11). The favoured formation of eight-membered 3,2'-cyclic acetals in lactose derivatives has been further demonstrated by acetonation of benzyl 2,3',6'-tri-O-benzyl-β-lactoside (13) and benzyl 2,6,3',6'-tetra-O-benzyl-b-lactoside (12). As an example of the synthetic utility of this acetonation reaction, the chiral macrocyclic polyhydroxyether 25 has been synthesized from benzyl 3',4'-O-isopropylidene-β-lactoside.

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