An expedient synthesis of salviadione

Nitroarenes and nitroalkenes as potential amino sources for the synthesis of N-heterocycles

Nitro-compounds are one of the cheapest and most readily available materials in the chemical industry and are commonly utilized as versatile building blocks. Previously, the synthesis of N-heterocycles was largely based on anilines. The utilization of nitroarenes and nitroalkenes for the synthesis of N-heterocyclic compounds can save at least one step, however, as compared to anilines. Thus, considerable attention has been paid to nitroarenes and nitroalkenes as new potential amino sources. Significant progress has been made in the reductive cyclization of nitroarenes or nitroalkenes to access various N-heterocycles in recent years. Herein, we comprehensively summarize the recent progress in the construction of N-heterocycles using nitroarenes and nitroalkenes as potential amino sources. The compatibility of the reaction substrate, its mechanism, applications, advantages, and limitations in this field are also discussed in detail.

A palladium-catalyzed Barluenga cross-coupling - reductive cyclization sequence to substituted indoles

A short and flexible synthesis of substituted indoles employing two palladium-catalyzed reactions, a Barluenga cross-coupling of p-tosylhydrazones with 2-nitroarylhalides followed by a palladium-catalyzed, carbon monoxide-mediated reductive cyclization has been developed. A one-pot, two-step methodology was further developed, eliminating isolation and purification of the cross-coupling product. This was accomplished by utilizing the initially added 0.025 equivalents of bis(triphenylphosphine)palladium dichloride, thus serving a dual role in the cross-coupling and the reductive cyclization. It was found that addition of 1,3-bis(diphenylphosphino)propane and carbon monoxide after completion of the Barluenga reaction afforded, in most cases, significantly better overall yields.

Biomimetic synthesis of the natural product salviadione and its hybrids: discovery of tissue-specific anti-inflammatory agents for acute lung injury

Biomimetic synthesis of the natural product salviadione and its hybrids was achieved leading to tissue-specific anti-inflammatory agents for acute lung injury.

Acute lung injury (ALI) is an inflammatory disease with no effective pharmacological treatment. The therapeutic potential of the anti-inflammatory natural product tanshinone IIA (2) for ALI is seriously impaired by its poor pharmacokinetic (PK) properties. Inspired by the unique benzo[def]carbazole-3,5-dione (BCD) core of the natural product salviadione (5), a series of furan-fused BCD hybrids of 5 with 2 was rationally designed with the aim to improve both PK properties and the anti-inflammatory activity. A biomimetic synthetic approach featuring one-pot tandem N-heterocyclization was first developed for convenient assembly of salviadione (56% overall yield over 2 steps) and the designed hybrids (35–85% yields in one step). Compared to 2, most of the resulting compounds exhibited a markedly enhanced inhibitory effect against LPS-induced release of pro-inflammatory cytokines in macrophages. Particularly, compound 15a not only possessed the most potent activity in vitro, but also exhibited significantly improved metabolic stability (4- to 7-fold enhancement), pharmacokinetic properties (T_1/2 = 4.05 h; F = 30.2%), and preferable lung tissue distribution (11- to 300-fold selectivity). An in vivo study in mice showed that pretreatment with 15a at 5 mg kg^–1 distinctly attenuated LPS-induced ALI via lung tissue-specific anti-inflammatory actions, indicating that the furan-fused BCD core presents a unique chemotype with promising therapeutic potential for ALI.

Au-Catalyzed Synthesis of Thiopyrano[2,3-b]indoles Featuring Tandem Rearrangement and Hydroarylation

Gold(III)-catalyzed synthesis of 14-π electron heteroaromatic thiopyrano[2,3-b]indole is reported using conjugated enyne tethered indole sulfides, featuring skeletal rearrangement conjoined with intramolecular hydroarylation (via C3-H functionalization of the indole core) and oxidative aromatization. Subsequent Pd-catalyzed C-C coupling resulted in a 16-π electron heteroaromatic isothiochromeno[1,8,7-bcd]indole.

Double Palladium Catalyzed Reductive Cyclizations. Synthesis of 2,2'-, 2,3'-, and 3,3'-Bi-1H-indoles, Indolo[3,2-b]indoles, and Indolo[2,3-b]indoles

A palladium catalyzed, carbon monoxide mediated, double reductive cyclization of 1,4-, 1,3-, and 2,3-bis(2-nitroaryl)-1,3-butadienes to afford 2,2'-, 2,3'-, and 3,3'-biindoles, respectively, was developed. In contrast, reductive cyclizations of 1,2-bis(2-nitroaryl)ethenes were nonselective, affording mixtures of monocyclized indoles, indolo[3,2-b]indole, indolo[1,2-c]quinazolin-6(5H)-ones, and 5,11-dihydro-6H-indolo[3,2-c]quinolin-6-ones. Nonselective product formation was also observed from reductive cyclization of 1,1-bis(2-nitroaryl)ethenes, producing indolo[2,3-b]indoles and indolo[2,3-c]quinolin-6-ones. Carbon monoxide insertion to give the carbonyl containing products was the major or sole reaction path starting from 1,1- or 1,2-bis(2-nitroaryl)ethenes.