Key Oxa-Annulation and the D-Ring Atropisomerism

We attempted the key intramolecular oxa-[3 + 3] annulation reaction of diketo-enal 8 under high-dilution conditions at room temperature using piperidinium acetate salt in THF. We were delighted upon the discovery of the formation of the desired 

While the discovery of this novel D-ring atropisomerism reveals the unique and intricate architecture of these tricycles, it alerted to us the actual alignment of the C3 allyl methyl group in the desired ABD-tricycle 2 and, more importantly, the 

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