A Mild and Efficient Synthesis of Dinaphthofuran and Furo[3,2-c] coumarin Derivatives under Ambient Air

Abstract

A highly efficient, straightforward, and eco-friendly strategy for the synthesis of functionalized dinaphthofuran (2) derivatives has been achieved from β-tetralone via an intermolecular cross-coupling, cyclization, and dehydrogenation in a single step using 20 mol% ferric chloride catalyst in dimethyl sulfoxide. Likewise, the synthesis of highly functionalized furo[3,2-c]coumarin (4) derivative was accomplished from various 4-hydroxy-coumarins under identical reaction conditions through the formation of dicoumarol intermediate by insertion of methylene group at the C3-position of 4-hydroxycoumarin from DMSO, followed by reacting with another molecule of 4-hydroxycoumarins. The intermediate dicoumarol undergoes concomitant ring opening, cyclisation, and dehydrogenation, affording furocoumarin derivatives in good yields. The reaction conditions are mild and easily handled, without the use of any external oxidants, additives, or inert atmosphere. Later, the OH group at the 2-position of the benzoyl ring in the product was further explored to synthesise a new class of ether derivative 7, which can be converted into a triazole derivative 9. The salient features of this protocol are a broad substrate scope, good-to-excellent yields, a polyfunctional moiety, and products containing more than one pharmaceutically important motif.