Reactions of o-alkynylisocyanobenzenes with a
variety of alkanethiols (Alk-SH) provide the corresponding bis-thiolated
indole derivatives. The advantages of the reaction include metal-free,
room-temperature, mild reaction conditions and broad functional group
compatibility. The reaction proceeds via nucleophilic addition of
an alkanethiol to an isonitrile moiety, 5-exo cyclization,
followed by nucleophilic addition of an alkanethiol to a 3-alkylidene
indole intermediate. Density functional calculations on the electronic
structures and relative free energies of 5-exo and
6-endo cyclization pathways support that the 5-exo cyclization is preferable.
A new synthetic approach for the synthesis of indolo[2,3-b]quinolines and benzothieno[2,3-b]quinolines
has been developed by employing the freshly prepared o-alkynylisocyanobenzenes derived from o-alkynylformamide
derivatives as substrates. The synthetic transformations involved
chloride-ion-triggered 6-endo cyclization of o-alkynylisocyanobenzenes to generate 2-chloroquinolines
in situ, which further cyclized intramolecularly with nitrogen or
sulfur atom via a cascade process to provide the corresponding indolo[2,3-b]quinolines and benzothieno[2,3-b]quinolines,
respectively, in moderate to excellent yields.
A facile synthesis of various functionalized 3-substituted quinolin-2(1H)-ones through Ag(i) nitrate-catalyzed cyclization of o-alkynylisocyanobenzenes is described. The reaction allows rapid and convenient access to 3-substituted quinolin-2(1H)-one scaffolds in moderate to good yields.
An efficient synthesis of 2-sulfonyl- and 2-thiocyanato-3-substituted quinolines through sequential nucleophilic addition/cyclization of o-alkynylisocyanobenzenes is described.
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