Synthesis of fused oxazolocoumarins has been achieved from the one‐pot tandem reactions of o‐hydroxynitrocoumarins with benzyl alcohol in toluene under catalysis in a sealed tube at 150°C. The catalysis was performed by gold nanoparticles supported on TiO2 (0.4 mol% Au) or FeCl3 (5%) or silver nanoparticles supported on TiO2 (1.7 mol% Ag).
Pyrano- and dipyranocoumarins are classes of naturally occurring organic compounds
with very interesting biological activities. This review focuses on the synthetic
strategies for the synthesis of pyranocoumarins and dipyranocoumarins and the biological
properties of those compounds. The synthesis involves the formation of the pyran ring, at
first, from a coumarin or the formation of pyranone moiety from an existing pyran. Pyranocoumarins
and dipyranocoumarins present anti-HIV, anti-cancer, neuroprotective, antidiabetic,
antibacterial, antifungal, anti-inflammatory activities. Especially khellactones
and calanolides are usually potent and selective in anti-HIV activity. Decursin and decursinol
derivatives are effective as anticancer, neuroprotective, antidiabetic, antibacterial, and
antifungal agents.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.