(5aS,7S)-7-Isopropenyl-3-methyl-5a,6,8,9-tetrahydro-1H,7H-pyrano[4,3-b][1]benzopyran-1-one

A remarkable asymmetric induction was observed in the one-pot condensation reaction of (S)-(-)-perillaldehyde with 4-hydroxy-6-methyl-2-pyrone in the presence of L-proline which provided the title compound, C₁₆H₁₈O₃, a tricyclic pyrone, as a single diastereomer in 78% yield. As the configuration of the cyclohexane C atom holding the isopropenyl group is the same as that in the (S)-aldehyde substrate, the total absolute stereochemistry could be elucidated from its X-ray structure. The cyclohexane ring has a chair conformation in which the juncture H atom (H5a) is axially oriented and the isopropenyl substituent is equatorial.

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