Carbohydrate‐Derived 3,2‐Enolones in the Base‐Catalyzed Rearrangement to Highly Functionalized C4‐Quaternary 4‐Hydroxy‐2‐cyclopentenones

Abstract

3,4,6‐O‐benzylated β‐2‐ulosides were subjected to 3,4‐elimination, providing carbohydrate‐derived 3,2‐enolones. Reaction of these enolones under basic conditions in polar aprotic solvents afforded highly functionalized racemic 5‐alkoxy‐2‐benzyloxy‐4‐benzyloxymethyl‐4‐hydroxy‐2‐cyclopentenones. The influence of the nature of the base as well as solvent effects were investigated. The rearrangement products obtained from this reaction exhibit a 4‐hydroxy‐C4‐quaternary stereogenic center. In contrast, the rearrangement of comparable dihydropyran‐3‐ones was reported to furnish the C5‐quaternary 5‐hydroxy‐2‐cyclopentenones. Plausible mechanisms for the described rearrangement and subsequent isomerization processes are given.

Studies toward the Synthesis of Colletotrichamide A: Construction of the C19–C30 Segment of the Molecule

“…19 The primary alcohol of 21 was selectively protected as its tert-butyldimethylsilyl ether to give secondary alcohol 22 in 85% yield. 20 Secondary alcohol 22 was oxidized 21 with Dess-Martin periodinane to give ketone 23 with 87% yield. Reduction of ketone 23 with NaBH4 furnished the required sugar with mannose configuration 24.…”