Imidazole-catalyzed construction of bridged bicyclo [3.3.1] ketals via formal [3 + 3]-cycloaddition of naphthols and 2-hydroxyl chromene derivatives

Abstract

Bridged bicyclo[3.3.1]nonanes having the O,O-ketal subunit are widely found in medicinal compounds. While several acid-catalyzed approaches have been reported for the construction of ketals, this study discloses an imidazole-catalyzed modular construction of bicyclo[3.3.1]nonanes from naphthols/phenols and 3-acyl-2-hydroxyl chromenes. The proposed reaction pathway follows a formal [3 + 3] cycloaddition of phenols and an oxonium dipolar intermediate. The reaction is efficient regarding scalability, environmentally benign conditions, and resulting in the products in good to excellent yields.