Ag(I)-Promoted, Diastereoselective Cyclo-isomerization of N-Alkynyl-7-azaindole-2-carbinols. Selective Synthesis of syn-1,2-Diarylpyrrolo[1,2-a]indol-3-ones and (Z)-8-Benzylideneoxazolo[3',4'':1,5]pyrrolo[2,3-b]pyridines

Iodine-Catalyzed Regioselective C-3 Chalcogenation of 7-Azaindoles: Access to Benzothiophene-Fused 7-Azaindole Analogs

An iodine-catalyzed method has been reported for efficient regioselective C-3 sulfenylation, selenylation, thiocyanation, and selenocyanation of NH-free 7-azaindoles using thiophenols, diselenides, potassium thiocyanates, and selenocyanates, respectively. This approach showcases high efficiency and remarkable versatility, facilitating the synthesis of diverse chalcogenated 7-azaindoles. Additionally, the sulfenylated derivatives have been further diversified to generate a new array of benzothiophene-fused 7-azaindole cores of pharmaceutical interest. The synthetic flexibility of this protocol has been highlighted through the gram-scale synthesis of sulfonylated 7-azaindole-based bioactive 5-HT6 receptor agonists.

Cooperative Catalysis-Enabled (4 + 3) Cycloaddition of 2-Indolylmethanols with In Situ-Generated ortho-Naphthoquinone Methides

A cooperative catalysis-enabled (4 + 3) cycloaddition of 2-indolylmethanols with ortho-naphthoquinone methides (o-NQMs), which were in situ-generated from enynones, has been established in the presence of silver/Brønsted acid cocatalysts. In the reaction pathway, the key o-NQM intermediates were formed through Ag(I)-catalyzed cyclization of enynones, while the indole-based carbocation intermediates were generated via Brønsted acid-catalyzed dehydration of 2-indolylmethanols. By this approach, a wide range of seven-membered cyclohepta[b]indoles were synthesized in good yields with high efficiency under mild reaction conditions, which serves as a useful strategy toward constructing indole-fused seven-membered rings. Moreover, the catalytic asymmetric version of this (4 + 3) cycloaddition has been realized under the cooperative catalysis of Ag(I) with chiral phosphoric acid, which offered chiral cyclohepta[b]indole with a good enantioselectivity (75% ee). This work not only represents the first cooperative catalysis-enabled (4 + 3) cycloaddition of 2-indolylmethanols but also provides a good example for o-NQM-involved cycloadditions, which will contribute to the chemistry of 2-indolylmethanols and enrich the research contents of cooperative catalysis.

Iron-Mediated Hydrogen Atom Transfer Radical Cyclization of Alkenyl Indoles and Pyrroles Gives Their Fused Derivatives: Total Synthesis of Bruceolline E and H

The iron-mediated hydrogen atom transfer (HAT) reaction is efficaciously employed for the synthesis of dihydropyrroloindoles and dihydropyrrolizines via 5-exo-trig radical cyclization where indoles and pyrroles are used as an acceptor. This radical approach has also been extended for the synthesis of tetrahydrocyclopenta[b]indolones via the Baldwin-disfavored 5-endo-trig cyclization pathway. The formal synthesis of bruceolline J and the total synthesis of bruceollines E and H have been expeditiously carried out by employing the former strategy.