We describe here for the first time the synthesis of isochromenones fused to selenophenes. 5H‐Selenopheno[3,2‐c]isochromen‐5‐ones were obtained through a double intramolecular cyclization of methyl 2‐(organyl‐1,3‐diynyl)benzoate promoted by electrophilic species of selenium generated in situ by the reaction of dialkyl diselenides with Oxone®, using ethanol as solvent. The reactions were conducted satisfactorily under mild conditions, using a range of 1,3‐diynes and dialkyl diselenides as substrates. A total of sixteen unprecedent 5H‐selenopheno[3,2‐c]isochromen‐5‐ones were selectively obtained in moderate to good yields (40–86%) under reflux in an open flask and in short reaction times (1.0–2.5 h).magnified image
We
report a protocol for the synthesis of 3-organyl-4-(organylchalcogenyl)isoquinoline-2-oxides
via electrophilic cyclization between alkynylbenzaldoximes and diorganyl
dichalcogenides promoted by Oxone. A total of 21 3-organyl-4-(organylchalcogenyl)isoquinoline-2-oxides
were selectively obtained in yields of up 93% under an ultrasound
irradiation condition in short reaction times (10–70 min).
Additionally, the synthetic usefulness of the 3-phenyl-4-(phenylselanyl)isoquinoline-2-oxide
was demonstrated in the annulation reaction with 1-(2-bromophenyl)-3-phenylprop-2-yn-1-one
and in the deoxygenation reaction with phenylboronic acid.
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.
We report herein an alternative method
for the synthesis of seleno-dibenzocycloheptenones
and seleno-spiro[5.5]trienones through the radical cyclization
of biaryl ynones in the presence of diorganyl diselenides, using Oxone
as a green oxidizing agent. The reactions were conducted using acetonitrile
as the solvent in a sealed tube at 100 °C. The protocol is operationally
simple and scalable, exhibits high regioselectivity, and allows the
synthesis of 24 dibenzocycloheptenones/spiro[5.5]trienones in
yields of up to 99%, 17 of which are unpublished compounds. Additionally,
synthetic transformations of the prepared compounds, such as oxidation
and reduction reactions, are demonstrated.
Oxone is a commercially available oxidant, composed of a mixture of three inorganic species, being the potassium peroxymonosulfate (KHSO5) the reactive one. Over the past few decades, this cheap and environmentally friendly oxidant has become a powerful tool in organic synthesis, being extensively employed to mediate the construction of a plethora of important compounds. This review summarizes the recent advances in the Oxone-mediated synthesis of N-, O- and chalcogen-containing heterocyclic compounds, through a wide diversity of reactions, starting from several kinds of substrate, highlighting the main synthetic differences, advantages, the scope and limitations.
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