The reaction between phloroglucinol and vic polycarbonyl compounds: extension and mechanistic elucidation of Kimʹs synthesis for bipolarofacial bowl-shaped compounds

Kimʹs serendipitous synthesis of a novel cavitand by the one-pot reaction between phloroglucinol and ninhydrin was revisited and extended. A much deeper cavitand was obtained by replacing ninhydrin with benzo[f]ninhydrin. Performing the reaction in a stepwise manner, employing both ninhydrin and benzo[f]ninhydrin, provided ‘mixed bowls’ of lower symmetry. Other cyclic polyketones, such as 1,2-indanedione and alloxan, form with phloroglucinol only partially closed structures. Crystallographic studies of the intermediate compounds in this reaction confirm Kimʹs postulate that the bowl formation involves hemiketal ring-openings and rearrangements.