Enantioselective de Novo Synthesis of 4-Deoxy-d-hexopyranoses via Hetero-Diels–Alder Cycloadditions: Total Synthesis of Ezoaminuroic Acid and Neosidomycin

The de novo synthesis of carbohydrates constitutes an important aspect of organic chemistry, and its application toward deoxy sugars is particularly noteworthy in targeting biologically active compounds. The enantioselective preparation of 4-deoxy-d-ribo-, 4-deoxy-d-lyxo-, and 4-deoxy-d-xylo-hexopyranosides, along with their uronate counterparts has been successfully accomplished using hetero-Diels–Alder reactions as the key step. Jacobsen chromium(III) catalyst and a titanium–binaphthol complex have been used to successfully catalyze diene and aldehyde cycloadditions, leading to optically active dihydropyran templates. 6-Hydroxydesosamine, orthogonally protected ezoaminuroic acid, and neosidomycin were synthesized using a comparative study. Also, a novel chiron approach to 4-deoxy-lyxo-hexopyranosiduronic acid methyl ester derivatives was efficiently accomplished starting from readily accessible starting materials. This work represents a systematic and comprehensive study toward a de novo synthesis of 4-deoxy-hexopyranoses via enantioselective hetero-Diels–Alder reactions.