Synthesis of indole-fused scaffolds via [3+3] cyclization reaction of 2-indolylmethanols with quinone imines

Copper-Catalyzed [3 + 2] Annulation of O-Acyl Oximes with 4-Sulfonamidophenols for the Synthesis of 5-Sulfonamidoindoles and 2-Amido-5-sulfonamidobenzofuran-3(2H)-ones

A copper-catalyzed [3 + 2] annulation of O-acyl oximes with 4-sulfonamidophenols is developed. The advantage of this method lies in the concurrent double activation of two substrates to form nucleophilic enamines and electrophilic quinone monoimines. The substituent on the α-carbon of O-acyl oxime determines two different reaction pathways, thereby leading to the selective generation of 5-sulfonamidoindoles and 2-amido-5-sulfonamidobenzofuran-3(2H)-ones.

Recent Advances in the Domino Annulation Reaction of Quinone Imines

Quinone imines are important derivatives of quinones with a wide range of applications in organic synthesis and the pharmaceutical industry. The attack of nucleophilic reagents on quinone imines tends to lead to aromatization of the quinone skeleton, resulting in both the high reactivity and the unique reactivity of quinone imines. The extreme value of quinone imines in the construction of nitrogen- or oxygen-containing heterocycles has attracted widespread attention, and remarkable advances have been reported recently. This review provides an overview of the application of quinone imines in the synthesis of cyclic compounds via the domino annulation reaction.

Aryliodonium Salt-Induced Regioselective Access to meta-Substituted Anilines by Arylation of Azoles

A highly efficient aryliodonium salt-induced regioselective access to meta-substituted anilines by arylation of azoles has been developed under catalyst-free conditions. This efficient transformation provides a facile and scalable approach to a wide range of biologically active N-arylazoles with moderate to high yields. According to the control experiments, two plausible pathways, including a Michael pathway and a free radical coupling pathway, for the reaction were proposed.

Regioselective Reaction of 2-Indolylmethanols with Enamides

A highly regioselective reaction of 2-indolylmethanols with enamides has been developed at room temperature by using AlCl₃ as a catalyst. A wide range of hybrids (40 examples) of indoles and enamides were obtained in moderate to good yields (up to 98% yield). This transformation represents the efficient way to introduce biologically important indoles and enamides skeleton into structurally complex hybrids.

Diversity synthesis of indole derivatives via catalyst control cyclization reaction of 2-indolylmethanols and azonaphthalene

A series of indole-fused scaffolds and derivatives was synthesized via the cyclization reaction of 2-indolylmethanols with azonaphthalene. These reactions were realized under mild reaction conditions through catalyst control, providing structurally diverse indole derivatives with moderate to excellent yields. This protocol also shows good substrate adaptability, especially in six-membered ring products.

La(OTf)3 facilitated self-condensation of 2-indolylmethanol: construction of highly substituted indeno[1,2-b]indoles

The Lewis acid-promoted self-condensation of 2-indolylmethanols has been revealed. On treatment with La(OTf)₃, highly substituted indeno[1,2-b]indole derivatives have been synthesized by using easily accessible 2-indolylmethanols with up to 94% yields. The utility of this method is further highlighted by evaluating the initial photophysical properties of some prepared products, indicating that the protocol may have potential applications in the construction of novel fluorescent materials.

2-Indolymethanols as 4-atom-synthons in oxa-Michael reaction cascade: access to tetracyclic indoles

The first Brønsted acid-catalyzed oxa-Michael reaction cascade of 2-indolylmethanols with trione alkenes was accomplished. By using this practical approach, a variety of tetracyclic indoles were readily created in an ordered sequence with excellent regio- and diastereoselectivity. 2-Indolylmethanols commendably served as four-atom synthons, as opposed to the common three-atom synthons in the previous literature reports. The regioselectivity issue was well handled by the employment of a strong Brønsted acid catalyst. In addition, its dual role in activation of substrates via hydrogen-bonding interaction and acceleration of subsequent intramolecular cyclization and dehydration was proposed to account for the high reaction efficiency.