(7aR*,7bR*)-7a,7b-Dihydro-15Н-dibenzo[f,f’]cyclopenta[1,2-b:5,4-b’]dichromene

The reaction of a 2-naphthol-derived Mannich base with the push–pull 5-morpholinopenta-2,4-dienal under acidic conditions unexpectedly afforded (7aR*,7bR*)-7a,7b-dihydro-15H-dibenzo[f,f']cyclopenta[1,2-b:5,4-b']dichromene. The structure of this product was unambiguously confirmed by NMR spectroscopy and X-ray diffraction analysis. A plausible mechanism involves the in situ generation of 1,2-naphthoquinone-1-methide, followed by a [4 + 2] cycloaddition and a subsequent interrupted iso-Nazarov cyclization. In this process, the enol tautomer of the resulting fused cyclopentenone is trapped by a second equivalent of the 1,2-naphthoquinone-1-methide, leading to the observed polycyclic framework.