Synthesis of Cyclopenta[b]indoles via Rhodium‐Catalyzed Cascade Migration‐Annulation of 1‐Sulfonyl‐1,2,3‐triazoles and Indoles

Abstract

A rhodium-catalyzed cascade 1,3-sulfinate migration, intermolecular [3 + 2] annulation of 1-sulfonyl-1,2,3-triazoles and indoles was achieved. The one-pot protocol provided a method to construct cyclopenta[b]indoles bearing four stereocenters in 45% to 99% yields with 1.6:1 to > 20:1 diastereoselectivities.In addition, cyclopenta [b]indoles could be transformed into a variety of functionalized compounds, demonstrating the synthetic value of this migration-annulation strategy in ring system synthesis.

Lewis-Acid-Catalyzed (3+2) Annulation of 2-Indolylmethanols with Propargylic Alcohols to Access Cyclopenta[b]indoles

“…Other common triflates, such as Bi(OTf)3, Yb(OTf)3, Cu(OTf)2, and AgNTf2, all promoted the reaction and gave the desired cyclopenta[b]indole product in moderate yields (entries 2-5, 13-70%). Sc(OTf)3 was found to be the best catalyst, and we then further evaluated the effect of the solvent (entries [6][7][8][9][10][11][12][13][14][15][16][17]. Apart from dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) (entries 14 and 15), many common solvents worked well, providing 3a in moderate yields ranging from 41% to 78% (entries 8-16).…”

“…Owing to their important biological properties, various synthetic protocols have been developed for preparing cyclopenta[ b ]indoles. Among these protocols, the (3+2) annulation of 2-indolylmethanols and olefins is an atom-economic strategy for the synthesis of these fused indole derivatives [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. In recent years, 2-indolylmethanols have become intriguing reactants because of their unique properties of electrophilicity and nucleophilicity at the C3 position [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ].…”

Molecular-iodine catalyzed selective construction of cyclopenta[b]indoles from indoles and acetone: a green gateway to indole-fused cycles

“…8,9 Some of the prominent approaches were based on [3 + 2]cycloaddition, [10][11][12] Nazarov cyclization, 13,14 Michael addition/ Friedel-Crafts process, 15,16 and various acid-promoted [17][18][19] and transition metal-mediated cyclization processes. [20][21][22][23] However, the majority of the processes relied on pre-functionalized aniline or indole derivatives, requiring specialized designing and multistep preparation of the starting com-pounds. 24 Hence, the quest for a simple process from readily available starting materials is highly desirable.…”

Copper-Catalyzed Synthesis of Furan-Tethered Benzocyclobutenes via Carbene-Mediated 1,4-Sulfinate Migration-Annulation

“…C yclobutane derivatives have garnered sustained interest within the chemical community. 1 Notably, benzocyclobutene occupies a significant position as a key synthetic intermediate, frequently utilized as a diene precursor for Diels−Alder reactions, both intermolecularly and intramolecularly. 2 Furthermore, benzocyclobutene derivatives exhibit a high degree of selectivity in their interactions with biological receptors, which has led to their widespread application in the pharmaceutical industry.…”