The importance of glycals as useful organic substrates and intermediates in carbohydrate chemistry is well recognized and they are extensively used as glycosylating agents, especially in the synthesis of 2-deoxy sugars and oligosaccharides and as precursors of C-glycosyl compounds. They are also widely recognized as versatile chiral building blocks in multistep organic syntheses. These applications often require availability of selectively protected glycals. Benzyl ethers are widely used as a protective group in sugar chemistry because of their stability in both acidic and basic conditions and the ability to remove them in neutral conditions simply by catalytic hydrogenation using Pd/C, even in the presence of many other protective groups. Up to this point, various methods have been used to obtain selective benzylated carbohydrates-all of them multistep processes. We propose a novel approach that selectively and efficiently produces 4-substituted derivatives directly from peracetylated glycals. The usefulness of this easily scalable, high-yield, one-pot synthetic process was demonstrated by the synthesis of 4-O-benzylated glycals directly from per-O-acetylated-D-glucal, -D-galactal, -L-fucal and -L-rhamnal. We will discuss the synthetic procedures and mechanistic origins of the observed selectivity.

Facile, selective one-pot synthesis of 4-O-benzylated glycals

247th National Meeting (2014)

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