Exploitation of Furanoid 5‐Azido‐3‐C‐Branched‐Chain Sugars Towards Highly Functionalized Nitrogen‐Containing Carbohydrate Derivatives

Abstract

The ability of easily accessed 1,2‐O‐protected 5‐azido‐3‐C‐(ethoxycarbonyl)methylenefuranoses to serve as precursors for the generation of imino sugar derivatives containing an α,β‐unsaturated lactone or ketone functionality has been investigated. A key aspect was the propensity of the corresponding deprotected δ‐amino α,β‐unsaturated esters to undergo 5‐aminofuranose/iminopyranose isomerization. Acid hydrolysis of the δ‐amino (Z)‐α,β‐unsaturated ester followed by treatment with base led to a butenolide‐containing N‐ethylformamide arising from a rearrangement of the imino‐sugar‐fused butenolide intermediate induced by the conjugated system. When carrying out the ring expansion step under neutral conditions, a 2‐keto imino sugar was obtained that was readily converted into a 1,2‐dihydropyridin‐3‐one by acetylation. Furthermore, reduction of the δ‐azido (E)‐α,β‐unsaturated ester to the amine was followed by spontaneous intramolecular cyclization, providing the related furanose‐fused unsaturated δ‐lactam.