One-pot Synthesis of Fused Dipyranocoumarins from Dihydroxycoumarins and Propargyl Chlorides under Microwave Irradiation

Dipetalolactone and 4-methyldipetalolactone are prepared in excellent yield by a one-pot tandem propargylation/Claisen rearrangement/cyclization reaction of the corresponding 5,7-dihydroxycoumarins with 3-chloro-3-methylbut-1-yne in the presence of Cs2CO3 under microwave irradiation. The analogous reactions of propargyl chloride with esculetins or 5,7-dihydroxycoumarins led to dipropargyloxy derivatives. The later by treatment with gold nanoparticles supported on TiO2 or BF3.Et2O in N,N-dimethylformamide (DMF) under microwave irradiation resulted in very good to excellent yield to the corresponding fused dipyranocoumarins. The reactions of esculetins with 3-chloro-3-methylbut-1-yne gave mainly exomethylene fused dioxino[g]coumarins.