Cascade Reaction to Selectively Synthesize Multifunctional Indole Derivatives by Ir^III‐Catalyzed C−H Activation

Abstract

An effective and condition-controlled way to synthesize with high selectivity a variety of functionalized indoles with potent biological properties has been developed. Notably, 2,4-dialkynyl indole products were obtained by direct double CÀ H bond alkynylation, whereas alkynyl at the C4 position could convert to carbonyl to generate 2alkynyl-3,4-diacetyl indoles fast and effectively. Additionally, a one-pot relay catalytic reaction led to 2,5-di-alkynyl-3,4diacetyl indoles when using a carbonyl group as the directing group and by controlling the type and quantity of additives. A possible mechanism was proposed based on many studies including deuterium-exchange experiments, the necessary conditions of product conversion, and the effect of water on the reaction.

Transition-Metal-Catalyzed Directing-Group-Assisted C4-H Carbon–Carbon Bond Formation of Indole

“…Recently, a double alkynylation of the indole core was disclosed by the Dong group under Ir(III)-catalysis with the aid of a weakly chelating carbonyl auxiliary (Scheme 10D). 31 Bromo alkyne coupled twice to furnish 2,4-dialkynylated indoles in good yield. The authors revealed that the specific combination of additives is crucial for the di-alkynylation.…”

Weak‐Chelation Assisted Regioselective Indole C(4)‐Alkynylation via Six‐Membered Cobaltacycle Intermediate

“…[16] Recently, the Dong group reported an iridium(III)-catalysed 2,4 di-alkynylation of indole using (bromo-ethynyl)triisopropylsilane as the alkylating agent (Figure 1b). [17] However, these works focused on the use of expensive transition metals such as Iridium and synthetically less accessible alkynylating agents. Though cobalt-catalyzed alkynylation [18] is reported, yet there is no report for Cp*Co(III)-catalyzed regioselective C4-alkynylation of indole.…”

Solid‐Phase Lipase‐CuNPs Biohybrids as Catalysts for One‐Pot Parallel Synthesis of 2,3,4‐Triacetyl‐D‐Gluconic Acid

“…[7] The development of cascade or parallel reaction systems represents the perfect strategy to produce these semiprotected monosaccharides, as they display several advantages compared to a typical single reaction, such as atom economy, step-saving, and high yield, therefore providing high efficiency to the chemical process. [8][9][10][11] In particular, regioselective biocatalytic strategies and metal-catalysis have been successfully applied in carbohydrate chemistry, [12] thus a combination of both would be an ideal task, low exploited until now. [13] However, a proper design of enzyme-metal combination is challenging, because these two types of catalysts often deactivate mutually and the reaction conditions for one cannot be applied to the other.…”

“…The development of cascade or parallel reaction systems represents the perfect strategy to produce these semiprotected monosaccharides, as they display several advantages compared to a typical single reaction, such as atom economy, step‐saving, and high yield, therefore providing high efficiency to the chemical process [8–11] …”