Nazarov Cyclization of Geminal-Benzoyl-Phenyl Allenes in Triflic Acid: A Synthetic Route to Pallidol-like Structures

Benzoyl substituted allenes in Brønsted superacid TfOH at room temperature afford Nazarov cyclization products, E-/Z-alkylidene indanones. In TfOH at a higher temperature of 70 °C, allenes bearing geminal benzoyl and phenyl substituents undergo further transformations, yielding fused indano-indanones. The latter have been used as precursors in the stereoselective synthesis of the structural analogue of the natural compound, Pallidol.