A Concise Asymmetric Synthesis of Torcetrapib

Facile Transfer Hydrogenation of N-Heteroarenes and Nitroarenes Using Magnetically Recoverable Pd@SPIONs Catalyst

Catalysts with active, selective, and reusable features are desirable for sustainable development. The present investigation involved the synthesis and characterization of bear-surfaced ultrasmall Pd particles (<1 nm) loaded onto the surface of magnetic nanoparticles (8-10 nm). The amount of Pd loading onto the surface of magnetite is recorded as 2.8 wt %. The characterization process covered the utilization of scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), inductively coupled plasma (ICP), and X-ray photoelectron spectroscopy (XPS) methods. The Pd@Fe3O4 catalyst has shown remarkable efficacy in the hydrogenation of quinoline, resulting in the production of >99% N-ring hydrogenated (py-THQ) product. Additionally, the catalyst facilitated the conversion of nitroarenes into their corresponding aniline derivatives, where hydrogen was achieved by H2O molecules with the aid of tetrahydroxydiboron (THDB) as an equilibrium supportive at 80 °C in 1 h. The high efficiency of a transfer hydrogenation catalyst is closely related to the metal-support synergistic effect. The broader scope of functional group tolerance is evaluated. The potential mechanism underlying the hydrogenation process has been elucidated through the utilization of isotopic labeling investigations. The application of the heterocyclic compound hydrogenation reaction is extended to formulate the medicinally important tubular polymerization inhibitor drug synthesis. The investigation of the recyclability of Pd@Fe3O4 has been conducted.

One-Pot Stereoselective Synthesis of Furantetrahydroquinoline Derivatives Using d/l-Ribose with a 2,3-O-Isopropylidene Group

An efficient and convenient strategy has been successfully developed for the preparation of novel furantetrahydroquinoline derivatives using d/l-ribose with a 2,3-O-isopropylidene group through the aza-Diels-Alder mechanism. This method has high atom and step economy, high stereoselectivity, and gram-scale synthesis (yield 67%).

Enantioselective Friedel-Crafts Alkylation of Indoles with β,γ-Unsaturated α-Ketoesters Catalyzed by New Copper(I) Catalysts

New Cu(I) catalysts are effective in enantioselective Friedel-Crafts alkylation of a variety of indoles with different β,γ-unsaturated α-ketoesters. A control study shows that such a catalyst system is less sensitive to air, and the reactions can be carried out without special cares such as glovebox operation or moisture/oxygen-free conditions. Preliminary computation results suggest that there exists π-π stacking between the substrate and the catalyst, and such an interaction seems to play a role in stabilizing the reaction intermediate and enhancing the stereoselectivity of the reactions. The desired products can be obtained in up to 98% yield at 99% enantiomeric excess. The same high enantioselectivity can be observed when the reaction is carried in a gram scale, indicating a good scalability of the catalyst system in enantioselective Friedel-Crafts alkylation of different indoles with β,γ-unsaturated α-ketoesters.

Enantio- and diastereoselective double Mannich reaction of malononitrile with N-Boc imines using quinine-derived bifunctional organoiodine catalyst

A chiral quinine-derived organic base catalyst with halogen bond donor functionality was used to catalyze the asymmetric double Mannich reaction of malononitrile with N-Boc and N-Cbz imines to afford 1,3-diamines in excellent yields with high enantio- and diastereoselectivities. With 2.2 equiv. of a single imine electrophile, symmetrical 1,3-diamines were obtained, whereas, with two different imine partners, unsymmetrically substituted 1,3-diamine was obtained. The monohydration of the double Mannich product was also achieved.

Facile syntheses of tetrahydroquinolines and 1,2-dihydroquinolines via vinylogous cascade hydride transfer/cyclization

The medicinally significant 3-monosubstituted tetrahydroquinolines and 1,2-dihydroquinolines were controllably constructed via redox-neutral vinylogous cascade condensation/[1,5]-hydride transfer/cyclization in EtOH.

Enamides and dienamides in phosphoric acid-catalysed enantioselective cycloadditions for the synthesis of chiral amines

This feature article describes how enamides and dienamides can participate in chiral phosphoric acid catalyzed enantioselective cycloadditions to prepare a wide range of cyclic amines.

Intramolecular Umpolung Allylation of Imines

An intramolecular umpolung allylation of imines is reported. This reaction occurs via the intermediacy of 2-azaallyl anions. It could proceed either under transition-metal-catalyzed conditions or under transition-metal-free conditions. Importantly, this approach afforded trans-3-vinyl-4-aminochromanes with high diastereoselectivity, while conventional, nonumpolung methods often display high cis-selectivity.

Recent Advances in Metal-Catalyzed Asymmetric 1,4-Conjugate Addition (ACA) of Nonorganometallic Nucleophiles

The metal-catalyzed asymmetric conjugate addition (ACA) reaction has emerged as a general and powerful approach for the construction of optically active compounds and is among the most significant and useful reactions in synthetic organic chemistry. In recent years, great progress has been made in this area with the use of various chiral metal complexes based on different chiral ligands. This review provides comprehensive and critical information on the enantioselective 1,4-conjugate addition of nonorganometallic (soft) nucleophiles and their importance in synthetic applications. The literature is covered from the last 10 years, and a number of examples from before 2007 are included as background information. The review is divided into multiple parts according to the type of nucleophile involved in the reaction (such as C-, B-, O-, N-, S-, P-, and Si-centered nucleophiles) and metal catalyst systems used.

Iodine catalyzed reduction of quinolines under mild reaction conditions

A reduction of quinolines to synthetically versatile tetrahydroquinoline molecules with I₂ and HBpin is described. In the presence of iodine (20 mol%) as a catalyst, reduction of quinolines and other N-heteroarenes proceeded readily with hydroboranes as the reducing reagents. The broad functional-group tolerance, good yields and mild reaction conditions imply high practical utility.

Highly efficient asymmetric construction of novel indolines and tetrahydroquinoline derivatives via aza-Barbier/C–N coupling reaction

An efficient approach towards stereoselective synthesis of chiral indolines and tetrahydroquinolines via Zn-mediated allylation of chiral-N-tert-butanesulfinyl imines and intramolecular C–N cross-coupling is described.

Levonantradol: asymmetric synthesis and structural analysis

The first asymmetric synthesis of a synthetic cannabinoid levonantradol was accomplished, and the 3-D solution structure of its core architecture was confirmed by NMR and computational methods.

Facile synthesis of functionalized tetrahydroquinolines via domino Povarov reactions of arylamines, methyl propiolate and aromatic aldehydes

In the presence of p-toluenesulfonic acid as catalyst the domino reaction of arylamines, methyl propiolates and aromatic aldehydes in ethanol proceeded smoothly to give polysubstituted 1,2,3,4-tetrahydroquinolines in moderate yields. The reaction is believed to involve the Povarov reaction of in situ generated β-enamino ester with the in situ formed aromatic imine.

Brønsted-acid-catalyzed asymmetric multicomponent reactions for the facile synthesis of highly enantioenriched structurally diverse nitrogenous heterocycles

Optically pure nitrogenous compounds, and especially nitrogen-containing heterocycles, have drawn intense research attention because of their frequent isolation as natural products. These compounds have wide-ranging biological and pharmaceutical activities, offering potential as new drug candidates. Among the various synthetic approaches to nitrogenous heterocycles, the use of asymmetric multicomponent reactions (MCRs) catalyzed by chiral phosphoric acids has recently emerged as a particularly robust tool. This method combines the prominent merits of MCRs with organocatalysis, thus affording enantio-enriched nitrogenous heterocyclic compounds with excellent enantioselectivity, atom economy, bond-forming efficiency, structural diversity, and complexity. In this Account, we discuss a variety of asymmetric MCRs catalyzed by chiral phosphoric acids that lead to the production of structurally diverse nitrogenous heterocycles. In MCRs, three or more reagents are combined simultaneously to produce a single product containing structural contributions from all the components. These one-pot processes are especially useful in the construction of heterocyclic cores: they can provide a high degree of both complexity and diversity for a targeted set of scaffolds while minimizing the number of synthetic operations. Unfortunately, enantioselective MCRs have thus far been relatively underdeveloped. Particularly lacking are reactions that proceed through imine intermediates, which are formed from the condensation of carbonyls and amines. The concomitant generation of water in the condensation reaction can deactivate some Lewis acid catalysts, resulting in premature termination of the reaction. Thus, chiral catalysts typically must be compatible with water for MCRs to generate nitrogenous compounds. Recently, organocatalytic MCRs have proven valuable in this respect. Brønsted acids, an important class of organocatalysts, are highly compatible with water and thereby offer great potential as chiral catalysts for multicomponent protocols that unavoidably release water molecules during the course of the reaction. We present a detailed investigation of several MCRs catalyzed by chiral phosphoric acids, including Biginelli and Biginelli-like reactions; 1,3-dipolar cycloadditions; aza Diels-Alder reactions; and some other cyclization reactions. These approaches have enabled the facile preparation of 3,4-dihydropyrimidinones, pyrrolidines, piperidines, and dihydropyridines with high optical purity. The synthetic applications of these new protocols are also discussed, together with theoretical studies of the reaction transition states that address the regio- and stereochemistry. In addition, we briefly illustrate the application of a recently developed strategy that involves relay catalysis by a binary system consisting of a chiral phosphoric acid and a metal complex. This technique has provided access to new reactions that generate structurally diverse and complex heterocycles. Enantioselective organocatalytic MCRs remain a challenge, but we illustrate success on several fronts with chiral phosphoric acids as the primary catalysts. Further progress will undoubtedly provide even better access to the chiral nitrogen-containing heterocycles that are not only prevalent as natural products but also serve as key chiral building blocks in organic synthesis.

Synthesis of optically active heterocyclic compounds using Pd-catalyzed asymmetric reactions as a key step

Highly enantioselective Pd(II)-catalyzed Michael addition, Mannich-type reaction, aldol reaction, fluorination, conjugate addition of amine, and conjugate reduction have been developed. Asymmetric synthesis of biologically interesting heterocyclic compounds, calycotomine, BMS-204352, torcetrapib, and warfarin, was achieved by using these Pd-catalyzed asymmetric reactions as a key step.