Abstract
Chitin is an abundant marine biomass consisting of N-acetylglucosamine (NAG) units. NAG is a source for 2-acetamide-2-deoxyisosorbide (ADI), a condensed five-membered ring compound potentially useful for producing nitrogen-containing polymers. The synthetic route of ADI from NAG consists of hydrogenation of NAG to 2-acetamide-2-deoxysorbitol (ADS) by a supported metal catalyst and subsequent dehydration reaction by a Brønsted acid catalyst. However, the dehydration step has remained a challenge due to low reactivity of the substrate and low selectivity. Here, we report a combination of Brønsted acid and Lewis acid catalysts for accelerating the ADS dehydration. The additional use of a catalytic amount of ytterbium triflate in the ADS dehydration by trifluoromethanesulfonic acid catalyst shortens the reaction time by one third and moreover increases the yield of ADI by changing regio-selectivity of the reaction. Mechanistic roles of the ytterbium complex are discussed based on the experimental evidences and density functional theory calculations.
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