Dearomative Alkylation-Based Two-Step cis-Diastereoselective Synthesis of Indoline-2,3-Fused Chromans and Tetrahydropyrans.

Herein, we describe a two-step, cis-diastereoselective synthesis of indoline-2,3-fused chromans from 3-substituted indoles. The method proceeds without intermediacy of ortho-quinone methides and leverages the dual function of TBS-protected 2-hydroxybenzyl iodides both as highly reactive alkylating agents in a t-BuONa/Et3B-promoted dearomative alkylation step and as a source of masked phenoxide nucleophiles in a subsequent TBAF-induced one-pot deprotection-cyclization step of the resulting indolenines. Importantly, this two-step protocol can also be extended to access indoline-2,3-fused tetrahydropyrans. These syntheses of indoline-2,3-fused chromans and tetrahydropyrans proceed with operational convenience, use easily accessible substrates and reagents, and feature broad substrate scope, high yields and complete diastereoselectivity. Furthermore, the synthesized products have the potential to undergo late-stage functionalization.

Synthesis of benzimidazole-fused 1,4-benzoxazepines and benzosultams spiro-connected to a 2-oxindole core via a tandem epoxide-opening/SNAr approach.

While hundreds of literature reports describe the preparation of spirooxindole-based five- and six-membered heterocycles, the construction of seven-membered heterocyclic rings spiro-connected to a 2-oxindole core has so far been less developed. Herein, we disclose a base-mediated (4 + 3) annulation of spiro-epoxyoxindoles and 2-(2-fluoroaryl)-1H-benzoimidazoles or 2-fluoro-N-arylbenzenesulfonamides toward the synthesis of two new classes of spirooxindole-based polycyclic systems. Mechanistically, this conceptually simple and high atom-economical reaction proceeds via an SN2-like intermolecular epoxide ring-opening, accompanied by a concomitant intramolecular SNAr reaction. From a synthetic aspect, the notable features of the process are its full regioselectivity, operational simplicity using readily available substrates under transition-metal-free conditions, high yields, and broad substrate scope.

Constructing spirooxindoles from non-oxindole precursors: a one-pot nitro-reduction/double lactamization approach to spiro[indoline-3,3'-quinoline]-2,2'-diones.

2-(2-Nitrobenzyl)-2-(2-nitrophenyl)malonates, readily prepared by SNAr-arylation of diethyl malonate with o-fluoronitrobenzenes, followed by SN2-alkylatioin of the resulting products with o-nitrobenzyl bromides, undergo a tandem Fe/AcOH-promoted nitro-reduction and double lactamization sequence to afford spiro[indoline-3,3'-quinoline]-2,2'-diones in high overall yields. The method is operationally simple, economical, and has a broad substrate scope. The synthetic practicality of this methodology was illustrated by performing the reaction on a gram scale with the same efficiency.

Diastereoselective Synthesis of Indoline- and Pyrrole-Embedded Tetracycles via an Unprecedented Dearomative Indole-C3-Alkylation/Aza-Friedel-Crafts Cascade Reaction.

Dearomative indole C3-alkylation─intramolecular iminium trapping cascade reaction of indole-C3-tethered nucleophiles is a well-known blueprint for accessing 2,3-fused indolines. In exploring this strategy, synthetic chemists have utilized diverse classes of electrophilic reagents. However, the tethered nucleophiles have mainly been limited to heteronucleophiles and enolates; exploitation of tethered arenes/heteroarenes remains unknown. We herein describe the first examples of pyrrole-intercepted dearomative indole C3-allylation and benzylation of indole-tethered pyrroles toward the synthesis of 2,3-cis-fused tetracyclic indolines featuring a C3 all-carbon quaternary stereocentre. Our methodology capitalizes on the capability of NaOtBu/Et3B combination to direct the intermolecular alkylation to take place regioselectively at the indole C3 position over the other reactive sites (indole N and C2 and pyrrole C2 positions) and leverages the high nucleophilicity of the pyrrole template for the concomitant aza-Friedel-Crafts ring closure that traditionally would require an additional acid-catalyzed synthetic step. This cascade reaction is accomplished with broad substrate scope and excellent yields and chemo-, regio-, and diastereoselectivities.

Hexafluoroisopropanol-Mediated Intramolecular Ring-Opening Cyclization of Indolyl-N-Tethered Epoxides: Tether-Length-Controlled Synthesis of 1,7- and 1,2-Fused Indoles.

Despite having the capability to construct benzo-fused heterocycles in complete atom economy and high chemo-, regio-, enantio-, and diastereoselectivities, intramolecular Friedel-Crafts epoxide arene cyclization (IFCEAC) remains underutilized in organic synthesis. The wide adaptation of this powerful Csp2-Csp3 bond-forming reaction, therefore, requires a broad understanding of the substrate scope to better impact heterocycle synthesis. Along this line, we investigated the applicability of IFCEAC for the synthesis of 1,7- and 1,2-fused indoles. In this article, we report the results of our systematic investigation into the scope and limitations of the first examples of the hexafluoro-2-propanol (HFIP)-mediated IFCEAC of readily accessible indolyl-N-tethered epoxides. We observed that the nature and position of the indole and epoxide substituents and the tether length separating these two reacting moieties have strong effects on the cyclization. This mild and transition-metal-free protocol delivered pyrrolo[3,2,1-ij]quinolin-5-ols in moderate to good yields from substrates bearing both a methylene linker that connects the indole and epoxide moieties and an electron-rich indole carbocyclic ring. Notably, the reactions required the presence of a π-activating aryl substituent on the reacting epoxide carbon atom. Interestingly, replacing the methylene tether with an ethylene unit resulted in regioswitching, which delivered the corresponding tetrahydropyrido[1,2-a]indol-8-ols in good to high yields. We could also successfully extend this methodology to pyrrolyl-N-tethered epoxides for a very high-yielding synthesis of tetrahydroindolizin-7-ols.

Diastereocontrolled Construction of Spiroindolenines via Hexafluoroisopropanol-Promoted Dearomative Epoxide-Indole Cyclization.

Herein, we report the discovery of the ipso-selective, dearomatizing spirocyclization of indole-tethered epoxides as a fundamentally new approach for constructing spiroindolenines equipped with three contiguous stereogenic centers under complete diastereocontrol (dr >99:1) and in high yields. Promoted by hexafluoroisopropanol, the protocol features a broad substrate scope, easy scale-up, and versatile transformations of the synthesized spiroindolenines.

A small molecule potent IRAK4 inhibitor abrogates lipopolysaccharide-induced macrophage inflammation in-vitro and in-vivo.

Increasing evidence supports vanillin and its analogs as potent toll-like receptor signaling inhibitors that strongly attenuate inflammation, though, the underlying molecular mechanism remains elusive. Here, we report that vanillin inhibits lipopolysaccharide (LPS)-induced toll-like receptor 4 activation in macrophages by targeting the myeloid differentiation primary-response gene 88 (MyD88)-dependent pathway through direct interaction and suppression of interleukin-1 receptor-associated kinase 4 (IRAK4) activity. Moreover, incubation of vanillin in cells expressing constitutively active forms of different toll-like receptor 4 signaling molecules revealed that vanillin could only able to block the ligand-independent constitutively activated IRAK4/1 or its upstream molecules-associated NF-κB activation and NF-κB transactivation along with the expression of various proinflammatory cytokines. A significant inhibition of LPS-induced IRAK4/MyD88, IRAK4/IRAK1, and IRAK1/TRAF6 association was evinced in response to vanillin treatment. Furthermore, mutations at Tyr262 and Asp329 residues in IRAK4 or modifications of 3-OMe and 4-OH side groups in vanillin, significantly reduced IRAK4 activity and vanillin function, respectively. Mice pretreated with vanillin followed by LPS challenge markedly impaired LPS-induced IRAK4 activation and inflammation in peritoneal macrophages. Thus, the present study posits vanillin as a novel and potent IRAK4 inhibitor and thus providing an opportunity for its therapeutic application in managing various inflammatory diseases.