Recent advances on the synthesis of acylindoles

TBHP/Et3N-Promoted Chemoselective Formylation and Peroxidation of Pyrrolo[2,1-a]isoquinolines

An efficient formylation of pyrrolo[2,1-a]isoquinoline derivatives has been reached by the use of TBHP (tBuOOH) and Et3N as the mediator. In this strategy, CHO and CDO can be readily incorporated into heteroarenes by the utilization of CHCl3 and CDCl3 as the carbonyl sources. Interestingly, a solvent-controlled chemoselectivity was observed. The use of PhCl as a solvent resulted in dearomatization and peroxidation of pyrrolo[2,1-a]isoquinolines, delivering functionalized peroxides in 53-64% yields.

DDQ/Fe(NO3)3-Catalyzed Aerobic Synthesis of 3-Acyl Indoles and an In Silico Study for the Binding Affinity of N-Tosyl-3-acyl Indoles toward RdRp against SARS-CoV-2

In the present study, we herein report a DDQ-catalyzed new protocol for the synthesis of substituted 3-acylindoles. Being a potential system for virtual hydrogen storage, introduction of catalytic DDQ in combination with Fe(NO₃)₃·9H₂O and molecular oxygen as co-catalysts offers a regioselective oxo-functionalization of C-3 alkyl-/aryllidine indolines even with scale-up investigations. Intermediate isolation, their spectroscopic characterization, and the density functional theory calculations indicate that the method involves dehydrogenative allylic hydroxylation and 1,3-functional group isomerization/aromatization followed by terminal oxidation to afford 3-acylindoles quantitatively with very high regioselectivity. This method is very general for a large number of substrates with varieties of functional groups tolerance emerging high-yield outcome. Moreover, molecular docking studies were performed for some selected ligands with an RNA-dependent RNA polymerase complex (RdRp complex) of SARS-CoV-2 to illustrate the binding potential of those ligands. The docking results revealed that few of the ligands possess the potential to inhibit the RdRp of SARS-Cov-2 with binding energies (-6.7 to -8.19 kcal/mol), which are comparably higher with respect to the reported binding energies of the conventional re-purposed drugs such as Remdesivir, Ribavirin, and so forth (-4 to -7 kcal/mol).

Boron Trifluoride Etherate Promoted Regioselective 3-Acylation of Indoles with Anhydrides

An efficient, high-yielding and scalable procedure for the regioselective 3-acylation of indoles with anhydrides promoted by boron trifluoride etherate under mild conditions was reported. This novel protocol provided a simple way to prepare 3-(benzofuran-2-yl) indole in three steps.

Synthesis of C-1 Deuterated 3-Formylindoles by Organophotoredox Catalyzed Direct Formylation of Indoles with Deuterated Glyoxylic Acid

Direct formylation of feedstock indoles with newly developed, cost-effective deuterated glyoxylic acid as formylation agent under visible light and air (O₂) as terminal oxidant has been developed. An isatin byproduct produced from the corresponding indole reactant serves as a facilitator for the formylation process. The simple, mild, metal- and oxidant-free protocol enables the synthesis of structurally diverse C1-deuterated 3-formylindoles with broad functional group tolerance and late-stage functionalization at a high level of D-incorporation (95-99%).

Formylation and Bromination of Pyrrolo[2,1-a]isoquinoline Derivatives with Bromoisobutyrate and Dimethyl Sulfoxide

We have developed an efficient formylation of pyrroloisoquinolines using bromoisobutyrate and dimethyl sulfoxide as carbonyl reagent. Various formylated pyrroloisoquinolines could be prepared in good yields (up to 94%). This formylation process can be easily scaled up to gram scale with good yield. In most cases of pyrroloisoquinolines without methoxy groups, the combination of bromoisobutyrate and dimethyl sulfoxide could act as a bromination reagent, delivering brominated pyrroloisoquinolines in acceptable to good yields (up to 82%).

Selective Synthesis of Pyrazolo[1,2-a]pyrazolones and 2-Acylindoles via Rh(III)-Catalyzed Tunable Redox-Neutral Coupling of 1-Phenylpyrazolidinones with Alkynyl Cyclobutanols

An unprecedented divergent synthesis of pyrazolo[1,2-a]pyrazolones and 2-acylindoles via Rh(III)-catalyzed [4 + 1] or [3 + 2] annulation of 1-phenylpyrazolidinones with alkynyl cyclobutanols through redox-neutral multiple bond activation by using -NH and -OH units as directing groups is presented. Notably, different annulation reactions were selectively achieved by simply adjusting the reaction conditions. With features such as simple procedures, easily accessible substrates, and high regio/chemoselectivity, these methods may find wide applications in related areas.

Regioselective N-1 and C-2 diacylation of 3-substituted indoles with arylglyoxal hydrates for the synthesis of indolyl diketones

A highly regioselective N-1 and C-2 diacylation of 3-substituted indoles with arylglyoxal hydrates to afford N-1 and C-2 indolyl diketones in moderate to good yields is described. Notably, the control of regioselectivity is achieved by small changes in the Cu catalyst, additive and solvent. Importantly, the intermediates for N-1 and C-2 diacylation were detected and two plausible pathways were also proposed.

A novel synthesis of N-hydroxy-3-aroylindoles and 3-aroylindoles

A straightforward indole synthesis via annulation of C-nitrosoaromatics with conjugated terminal alkynones was realised achieving a simple, highly regioselective, atom- and step economical access to 3-aroylindoles in moderate to good yields. Further functionalizations of indole scaffolds were investigated and an easy way to JWH-018, a synthetic cannabinoid, was achieved.

Copper-catalyzed synthesis of indolyl diketones via C–H oxidation/diacylation of indoles with arylglyoxal hydrates

Copper-catalyzed synthesis of indolyl diketonesviaC–H oxidation/diacylation of indoles with arylglyoxal hydrates is described.

Brønsted acidic ionic liquid-promoted direct C3-acylation of N-unsubstituted indoles with acid anhydrides under microwave irradiation

A green and efficient method for the synthesis of 3-acylindoles using a Brønsted acidic ionic liquid under microwave irradiation has been developed.