Protection with methoxyethoxy group

The synthesis of L-ribofuranose derivatives from 16a has been carried out by Walker and Hogenkamp (35). The procedure involves oxidation of the hydroxymethyl group of 16a with dimethyl sulfoxide N,N dicyclohexylcarbodiimide and acid hydrolysis of the protecting group to give L-riburonic acid, which was converted into methyl (methyl a,/ -ribofurano-sid)uronates (26). Reduction of 26 with sodium bis(2-methoxyethoxy)alu-minum hydride gave the chromatographically separable anomers of methyl L-ribofuranoside (27). 

Protection of ethyl L-lactate with a MEM group is easily accomplished by alkylation with (2-methoxyethoxy)methyl chloride in the presence of Hunig s base (2- 372) [100,116,117]. 

Acetylide 241 combines smoothly with electrophiles, in particular, aldehydes (Scheme 1-186). The adducts can be subjected to enzymatic racemate resolution and then converted by Lindlar hydrogenation or reduction with sodium bis(2-methoxyethoxy)-aluminum hydride ("Red-Al") into the cis- and tram-allylic alcohol, respectively. After diastereoselective dihydroxylation with osmium tetroxide and protection of the 1-hydroxyl group 2,6-dideoxy-6,6,6-trifluoro sugars are obtained (Scheme 1-186). ... 

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