Based on the electronic properties of different hybridized oxygen atoms (sp3versus sp2) in the structure of O,O-acetals containing an enol ether moiety, the chemoselective formation of oxocarbenium ions was realized to furnish diversified chiral heterocyclic compounds with excellent stereoselectivities by reacting with different types of nucleophiles. Additionally, an unexpected intramolecular oxocarbenium ion transfer was also reported to form polycyclic products containing the O,O-acetal functional group.
An asymmetric organocatalytic direct arylation approach to construct arylated quaternary stereogenic centers with a catalyst loading of 1 mol % is reported. The formation of the hemiketal moiety in stabilizing the hydroquinone intermediate proves to be important in leading to hydroquinone products instead of oxidation quinone products obtained in previously reported methods. A series of structurally and stereochemically complex heterocyclic frameworks are obtained, including spiro-, dispiro-, fused, and bridged heterocycles.
Starting from substituted racemic lactols, the combination of organo/gold catalytic system works extremely well providing epimeric bicyclic O,O-acetals as 5,6-, and 6,6-fused ring systems in good isolated yield with excellent enantioselectivities as pure diastereomers only after simple chromatographic purification. To highlight the synthetic potential, several oxygen-containing heterocycles were prepared smoothly via a diversityoriented sequential process with high regio-and stereoselectivity, which are important structural units found in natural products and bioactive unnatural molecules.
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