New Hybrid Type Squaramide Fused Amino Alcohol Organocatalysts for Enantioselective Diels-Alder Reaction of 3- Hydroxy-2-Pyridones with Maleimides

The hybrid type squaramide fused amino alcohol (SFAA) containing both Brønsted basic site and hydrogen bonding site in the molecule showed highly catalytic activity as an organocatalyst in the enantioselective Diels-Alder reaction (DA) of 3-hydroxy-2-pyridones with maleimides to afford the chiral endo-4-hydroxy-2-azabicyclo[2.2.2]octanes (4-hydroxy-isoquinuclidines) with excellent chemical yields and enantioselectivities (up to 95%, up to 98% ee). Particularly, the use of 4-brominated 2-pyridones afforded the corresponding chiral 4-hydroxyisoquinuclidines in both excellent chemical yield and enantioselectivity (95%, 98% ee) having an opposite absolute stereochemistry in comparison with the chiral endo-DA adduct from the reactions using common 3-hydroxy-2-pyridones. The obtained DA adducts could be used as synthetic precursors for the several natural products that have a broad spectrum of fascinating biologically activities.

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