Ruthenium-Catalyzed Cross Dehydrogenative Annulation of N-(7-Azaindole)benzamides with Maleimides: One-Step Access to Highly Functionalized Pyrroloisoquinoline

Ruthenium(II)-Catalyzed Annulation of Oximes with Maleimides: Synthesis of Pyrrolo[3,4-c]isoquinoline-1,3-diones

A series of pyrroloisoquinoline-1,3-diones has been synthesized using ruthenium(II) as the catalyst and oxygen as the oxidant in a straightforward manner. The reaction proceeds through a tandem C-C/C-N bond formation process between maleimides and ketoximes, providing a direct approach for the synthesis of the titled products. This operationally simple reaction procedure supplies suitable conditions for synthesizing diverse isoquinoline-based heterocycles with a range of functional groups in moderate to good yields and compatible with gram-scale synthesis. Furthermore, the compatibility of this reaction with oxygen as a green and environmentally friendly oxidant raises the importance of the present method.

Electrochemical Oxidative (4 + 2) Cyclization of Anilines and o-Phenylenediamines for the Synthesis of Phenazines

Phenazines, crucial constituents of nitrogen-containing heterocycles, widely exist in functional compounds. Herein, we report an anodic oxidative (4 + 2) cyclization between anilines and o-phenylenediamines for the uniform construction of phenazines in a simple undivided cell. Dual C-H amination followed by oxidation represents an outstanding step and atom efficiency. A sequence of phenazines is produced with excellent functional group tolerance at room temperature.

A rhodium-catalyzed cascade C-H activation/annulation strategy for the expeditious assembly of pyrrolidinedione-fused 1,2-benzothiazines

A cascade annulation strategy triggered by rhodium(III)-catalyzed C-H activation has been reported for the expeditious assembly of pyrrolidinedione-fused 1,2-benzothiazines from free NH-sulfoximines with maleimides under mild conditions. Without the need for inert atmosphere protection, a broad range of sulfoximines with maleimides were well tolerated, producing diverse fused-thiazine derivatives in moderate to good yields. Additionally, the late-stage transformation of the target product demonstrated the potential synthetic value of this protocol.

Unlocking New Prenylation Modes: Azaindoles as a New Substrate Class for Indole Prenyltransferases

Aza-substitution, the replacement of aromatic CH groups with nitrogen atoms, is an established medicinal chemistry strategy for increasing solubility, but current methods of accessing functionalized azaindoles are limited. In this work, indole-alkylating aromatic prenyltransferases (PTs) were explored as a strategy to directly functionalize azaindole-substituted analogs of natural products. For this, a series of aza-l-tryptophans (Aza-Trp) featuring N-substitution of every aromatic CH position of the indole ring and their corresponding cyclic Aza-l-Trp-l-proline dipeptides (Aza-CyWP), were synthesized as substrate mimetics for the indole-alkylating PTs FgaPT2, CdpNPT, and FtmPT1. We then demonstrated most of these substrate analogs were accepted by a PT, and the regioselectivity of each prenylation was heavily influenced by the position of the N-substitution. Remarkably, FgaPT2 was found to produce cationic N-prenylpyridinium products, representing not only a new substrate class for indole PTs but also a previously unobserved prenylation mode. The discovery that nitrogenous indole bioisosteres can be accepted by PTs thus provides access to previously unavailable chemical space in the search for bioactive indolediketopiperazine analogs.

Unexpected Cascade Sequence Forming the C(sp3)-N/C(sp2)-C(sp2) Bond: Direct Access to γ-Lactam-Fused Pyridones with Anticancer Activity

An unexpected Ugi cascade reaction was developed for the facile construction of γ-lactam-fused pyridone derivatives with high tolerance of substrates. A C(sp3)-N bond and a C(sp2)-C(sp2) bond were formed together, accompanied by a chromone ring-opening in Ugi adducts, under the basic conditions without any metal catalyst for the whole process. Screening data of several difficult-to-inhibit cancer cell lines demonstrated that 7l displayed a high cytotoxicity against HCT116 cells (IC50 = 5.59 ± 0.78 μM). Taken together, our findings revealed new insights into the molecular mechanisms underlying compound 7l and provided potential usage of this scaffold for cancer therapeutics.

Synthesis of Selenoflavones via Ruthenium-Catalyzed Selenylation of Unsaturated Acids

An efficient method for pharmaceutically useful selenoflavones via a ruthenium-catalyzed selenylation reaction is demonstrated. The ruthenium-catalyzed selenylation was applied to synthesize diverse alkenyl selenides from simple unsaturated acids/amides and diaryl diselenides. A wide range of differently substituted diaryl diselenides can be applied in this protocol with a good functional group with excellent stereo- and regioselectivity.

Rh(III)-Catalyzed [4 + 1] Annulation of Sulfoximines with Maleimides: Access to Benzoisothiazole Spiropyrrolidinediones

Rh(III)-catalyzed synthesis of benzoisothiazole spiropyrrolidinediones using sulfoximine as a directing group under a C-H activation and [4 + 1] annulation strategy with maleimides as a coupling partner is reported. The cyclization reaction was compatible with various substituted sulfoximine and maleimides. The deuterium-labeling studies were performed to investigate the mechanism of the reaction.

Ruthenium(II)-catalyzed oxidative dehydrogenation and hydroarylation of maleimides with phthalazinones - insights into additive-controlled product selectivity

Herein, we developed ruthenium(II)-catalyzed oxidative dehydrogenation and hydroarylation of maleimides with phthalazinones. The product selectivity is controlled by the additives, and the hydroarylated product was obtained in water, which is an important highlight of this study. Control experiments were conducted to elucidate a plausible mechanism. These experiments suggest the occurrence of an oxidative dehydrogenation pathway over E2-type elimination - the key step in producing Heck-type products.

Chemodivergent Synthesis of Indeno[1,2-b]indoles and Isoindolo[2,1-a]indoles via Mn(III)-Mediated or Electrochemical Intramolecular Radical Cross-Dehydrogenative Coupling

Chemodivergent synthesis of indeno[1,2-b]indoles and isoindolo[2,1-a]indoles from the same starting materials involving radical cross-dehydrogenative couplings have been developed. Mn(OAc)₃·2H₂O selectively promoted an intramolecular radical C-H/C-H dehydrogenative coupling reaction to provide indeno[1,2-b]indoles, while an intramolecular radical C-H/N-H dehydrogenative coupling reaction could proceed via electrochemistry to deliver isoindolo[2,1-a]indoles. Plausible mechanisms of the chemodivergent reactions were proposed.

Recent advances in transition-metal-catalyzed directed C-H alkenylation with maleimides

Transition-metal-catalyzed directed C-H alkenylation with maleimides has attracted much attention in recent years, as maleimide core moieties are present in various natural products and pharmaceuticals. In addition, these derivatives can be readily modified into biologically important compounds including succinimides, pyrrolidines and γ-lactams. The efficient chelation-assisted inert C-H bond activation strategy provides straightforward access to a wide array of structurally diverse molecules containing maleimide units. This review describes the major progress and mechanistic investigations on Heck-type reaction/cyclization of maleimides with organic molecules until early 2022.

Ruthenium-Catalyzed Regioselective C(sp2)-H Activation/Annulation of N-(7-Azaindole)amides with 1,3-Diynes Using N-Amino-7-azaindole as the N,N-Bidentate Directing Group

The ruthenium(II)-catalyzed regioselective annulation of N-(7-azaindole)amides with 1,3-diynes has been demonstrated. Bioactive N-amino-7-azaindole has been used as a new bidentate directing group to furnish an array of 3-alkynylated isoquinolones. Furthermore, the developed protocol works efficiently for both aryl- and heteroaryl-substituted amides producing a range of pharmacologically useful 7-azaindole-based isoquinolones with a wide range of functionality.