One–pot Selective Synthesis of 2,3‐Dihydro‐4H‐Furo[3,2‐c]coumarins by Palladium‐Catalyzed Silver‐Assisted Propargylation/Intramolecular 5‐exo–dig Cyclization

Abstract

A new catalytic system using bis(triphenylphosphine)palladium(II) dichloride and Ag2CO3 was developed for the one‐pot selective synthesis of dihydrofuro[3,2‐c]coumarin 3 from 4‐hydroxycoumarin (1) and propargylic carbonate 2 under the mild condition. Our catalytic system afforded distinct regioselectivity compared to reported methodologies using palladium catalysts, 2 and active methylene compounds. In addition, furo[3,2‐c]coumarin 4 was derived from 3 with Et3N. The proposed reaction mechanism involved 4‐hydroxycoumarin (1) reacting with the η1–(propargyl)palladium complex to generate a terminal alkyne, and subsequent intramolecular 5‐exo‐dig cyclization selectively synthesized 3 in one‐pot. The newly developed methodology is beneficial in the construction of a novel compound library related to furocoumarins with distinct regioselective preference.

Furo[3,2-c]coumarins carrying carbon substituents at C-2 and/or C-3. Isolation, biological activity, synthesis and reaction mechanisms

“…On the other hand, a similar transformation was reported under palladium catalysis, with Ag 2 CO 3 as oxidant, which results in 2,3-disubstituted compound 178 through the Et 3 N-mediated isomerization of the related exo-olens 177. 165…”

One-Pot Synthesis of 4H-Pyrano[3,2-c]coumarin Derivatives Catalyzed by Deep Eutectic Solvent

“…21 In addition, tetrabutylammonium bromide (TBAB) can be used to catalyze the reaction of 4-hydroxycoumarin with ethyl benzylidenecyanoacetate to synthesize pyrano [3,2-c]coumarin derivatives (Scheme 1b). 22 There have been many related reports on synthetic methods for these compounds using many catalysts, such as metal catalysts (Fe, Cu, Pd), [23][24][25][26][27][28] NaBr, 29 ZnO, [30][31][32] hexamethylenetetramine, 33 and potassium phthalimide. 34 The major disadvantages of using these catalysts are unsatisfactory yields, long reaction times, complicated operations, and high cost.…”