Catalytic allylation of native hexoses and pentoses in water with indium

Abstract

Carbohydrates are an abundant, inexpensive and renewable biomass feedstock that could be a cornerstone for sustainable chemical manufacturing, but scalable and environmentally friendly methods that leverage these feedstocks are lacking. For example, 1-allyl sorbitol is the foundational building block for the polypropylene clarifying agent Millad NX 8000, which is produced on the multi-metric ton scale annually, but the manufacturing process at present requires superstoichiometric amounts of tin1,2. The NX 8000 additives dominate about 80% of the global clarified polypropylene market3 and are used in concentrations of 0.01–1% during polypropylene production to improve its transparency and resistance to high temperatures, translating to 300–30,000 metric tons annually. The market volume of polypropylene in 2022 was approximately 79.01 million metric tons (MMT), with demand expected to rise by nearly 33% to 105 MMT by 2030 (ref. 4). The cost and sustainability benefits of clarified polypropylene are driving this demand, necessitating more clarifying agents5. Here we report a high-yielding allylation of unprotected carbohydrates in water using a catalytic amount of indium metal and either allylboronic acid or the pinacol ester (allylBpin) as donors. Aldohexoses, aminohexoses, ketohexoses and aldopentoses are all allylated in high yield under mild conditions and the indium metal is recoverable and reusable with no loss of catalytic activity. Leveraging these features, this process was translated to a scalable continuous synthesis of 1-allyl sorbitol in flow6 with high yield and productivity through Bayesian optimization of reaction parameters. A longstanding challenge in organic synthesis—the catalytic allylation of unprotected saccharides in an aqueous medium, a key step for the synthesis of Millad NX 8000—is achieved through a simple and efficient indium-catalysed nucleophilic allylation using a three-carbon-unit allylboronic acid or its pinacol ester.