Synthesis of 4-Selanyl- and 4-Tellanyl-1H-isochromen-1-ones Promoted by Diorganyl Dichalcogenides and Oxone

A new method was developed for the synthesis of 4-chalcogenyl-1H-isochromen-1-ones through the 6-endo-dig electrophilic cyclization of 2-alkynylaryl esters and diorganyl dichalcogenides under ultrasound irradiation. The reactions were performed under mild conditions, using Oxone as a green oxidant to promote the cleavage of the chalcogen-chalcogen bond in diorganyl diselenides and ditellurides to generate electrophilic species in situ. A total of 25 compounds were selectively obtained after 30-70 min, in good to excellent yields (74-95%). This procedure was extended to prepare 5H-selenopheno[3,2-c]isochromen-5-ones. Additionally, for the first time, the 4-chalcogenyl-1H-isochromen-1-ones were used as substrates in the thionation reaction, using Lawesson's reagent and microwave irradiation under solvent-free conditions, obtaining the thio derivatives in yields of up to 99% in only 15 min.

Modular synthesis of 3-substituted isocoumarins via silver-catalyzed aerobic oxidation/6-endo heterocyclization of ortho-alkynylbenzaldehydes

A method involving silver-catalyzed aerobic oxidation/6-endo heterocyclization of ortho-alkynylbenzaldehydes to yield 3-substituted isocoumarins is described. The developed protocol allows convenient access to a range of synthetically useful 3-substituted isocoumarins and related fused heterocyclolactones in good to high yields, using silver tetrafluoroborate as the catalyst, and atmospheric oxygen as the terminal oxidant and the source of endocyclic oxygen. Mechanistic studies suggest the involvement of a free-radical pathway.

Utilization of ortho-alkynylarylcarbonyl derivatives for creating structurally diverse chemical compounds

ortho-Alkynylarylcarbonyl compounds, including ketones, aldehydes, carboxylic acids, carboxylate esters and amides, have served as useful building blocks for synthetic chemists to prepare numerous classes of important molecules. Various synthetic conversions starting from ortho-alkynylarylcarbonyl precursors are made possible by their unique and enabling structures embedded with reactive carbonyl and alkyne functional groups. These functional groups can be converted directly and independently to other compounds by several reactions. This review highlights the use of these compounds as common precursors for the divergent synthesis of valuable molecules. Moreover, these ortho-alkynylarylcarbonyl compounds can be decorated with other functional group tethers which can lead to an even greater diversity of molecular scaffolds.

Lactonization of 2-Alkynylbenzoates for the Assembly of Isochromenones Mediated by BF3·Et2O

A general and efficient lactonization method of readily available 2-alkynylbenzoates affording biologically important isochromenones has been realized via a solely BF₃·Et₂O-mediated 6-endo-dig cyclization process under mild conditions. An alternative mechanistic pathway in which BF₃·Et₂O activates the carbonyl of the ester moiety, rather than the alkyne triple bond, was postulated on the basis of control experiment results. Gram-scale reaction and further application for the assembly of more complex molecules demonstrated the practicability of the protocol.

Silver triflate/p-TSA co-catalysed synthesis of 3-substituted isocoumarins from 2-alkynylbenzoates

A well-balanced composition of catalytic system partners makes the approach cheap, quick, regioselective, mild, general, scalable and high-yielding.