A versatile strategy for the synthesis of fused cyclopentenones, key structural motifs in biologically relevant compounds such as indenones and indole alkaloids, has been established successfully through regioselective palladium‐catalyzed cyclization of 2‐iodoaryl allenols.
A method for copper‐catalyzed aryltrifluoromethylation of N‐phenylcinnamamides is reported. This method provides a straightforward route to a variety of CF3‐containing 3,4‐dihydroquinolin‐2(1 H)‐ones with excellent regioselectivity and diastereoselectivity.
Novel copper‐catalyzed three‐component reactions of phenylacetonitrile, sulfur and DMF (dimethyformamide) for the selective preparation of N,N‐dimethylthiobenzamide and N,N‐dimethyl‐2‐phenylethanethioamides in yields of up to 96% are described.
A synthetically useful 1,3‐insertion reaction of a rhodium‐carbenoid into the C(sp2) H bond of simple indole is disclosed, which produces structurally divergent 2‐indolylenamides in good to excellent yields and decent chemo‐ and regioselectivities. The obtained tryptamine vinylogues can be transformed into biologically important tryptamine derivatives or 3,3′‐biindoles with ease.
A convenient gold‐catalyzed strategy for the synthesis of imidazo[1,2‐a]pyridine derivatives has been developed via gold carbene complexes. This transformation opens a new synthetic route to a variety of 3‐carbonyl‐substituted imidazo[1,2‐a]pyridines using air as oxidant affording the products in good yields.
The N‐heterocyclic carbene (NHC)‐catalyzed oxidative amidation of aromatic aldehydes with amines in the presence of N‐bromosuccinimide (NBS) as an oxidant has been developed for the synthesis of amides. This amidation strategy is tolerant to both the electronic and the steric nature of the aryl aldehydes employed. The present methodology was extended to chiral amino acid derivatives to generate the corresponding amides in good yields and excellent ee values (>98%).
A convenient palladium‐catalyzed tandem reaction of aryl iodides and salicyl N‐tosylhydrazones has been achieved to afford a series of compounds containing the novel spiro[benzofuran‐3,2′‐chromene] scaffold in moderate to good yields. This efficient catalytic reaction, which tolerates various functional groups, combines alkyne‐based 5‐exo‐dig cyclization, palladium(II) carbene migratory insertion and intramolecular cyclization, generating three new bonds in one reaction.
A straightforward assisted tandem palladium(II)‐ and palladium(0)‐catalyzed direct C‐3 and N‐4 arylation of quinoxalin‐2(1 H)‐ones with boronic acids and aryl halides in water as safe and cheap solvent is reported. This environmentally friendly catalytic protocol is compatible with a wide range of functional groups and allows construction of various biologically important quinoxalin‐2(1 H)‐one backbones.
A copper‐catalysed multicomponent coupling reaction between readily available (Z)‐3‐iodoacrylic acids, terminal alkynes, and primary amines was developed to smoothly access a small library of 5‐hydroxy‐1H‐pyrrol‐2(5H)‐ones in good yields. This practical and general process was applied to a short‐steps synthesis of the natural product pulchellalactam.
In order to investigate significant differences in asymmetric induction for pseudo enantiomeric carbohydrate olefin ligands in rhodium(I)‐catalysed 1,4‐addition reactions, we designed a set of new olefin ligands differing in relative configuration and pyranoside conformation. With these, we have successfully elucidated structural requirements for metal binding and also identified an improved alternative for one pseudo enantiomer. Furthermore, we report the efficient kinetic resolution of a racemic 4‐hydroxycyclopentenone derivative by 1,4‐addition.
A sequential one‐pot synthesis of Michael adducts of aroylmethylidenemalonates with activated aromatics is described. The method involves treatment of trans‐2‐aryl‐3‐nitro‐cyclopropane‐1,1‐dicarboxylates with boron trifluoride etherate to form aroylmethylidenemalonates in situ and then addition of activated aromatics such as indoles, carbazole, pyrrole, thiophenes, methoxybenzenes and benzodioxole followed by a catalytic amount of indium(III) triflate to the same reaction vessel. To prove the synthetic potential of the resulting Michael adducts, one of the adducts was transformed into a pharmaceutically interesting dihydropyridazinone derivative.
The first example of enantioselective nitronate protonation following Michael addition of a carbon nucleophile to an α,β,β‐trisubstituted nitroalkene is reported. An N‐sulfinylurea catalyst was employed to catalyze the addition of a variety of 3‐substituted pyrazol‐5‐one nucleophiles to trisubstituted nitroalkenes incorporating an oxetane or azetidine ring at the β‐position. The nitroalkane‐pyrazolone adducts were obtained with good yield and enantioselectivity. Furthermore, the Michael addition products can be reduced to the corresponding enantioenriched amines with minimal loss of enantiomeric purity.
This paper describes the aerobic oxidation of styrenes catalyzed by iron(III) chloride (FeCl3) to form β‐keto‐N‐alkoxyphthalimides in fair to good yields. This oxidative process employs mild conditions with green and atom efficient dioxygen (O2) as the oxidant.
An efficient route to 4‐cyanoquinolines via a palladium‐catalyzed cyanative reaction of 2‐alkynylbenzaldimines with isocyanides has been developed. The transformation proceeds through 6‐endo cyclization, isocyanide insertion, and cyanation. 4‐Amidylisoquinolines can be generated as well if water is involved in the reaction.
A method for using amine–borane complexes directly in palladium catalyzed borylation has been developed. The reaction proceeds through the sequential formation of a boronium species followed by deprotonation leading to the aminoborane. This reagent is then directly used in the borylation process leading, after work‐up, to various boronic acid derivatives. The reaction was applied to (hetero)aryl triflates, iodides, bromides and chlorides.
An efficient protocol has been developed for the methylenation of imidazo[1,2‐a]pyridines using dimethylacetamide (DMA) as methylene source in the presence of vanadyl acetylacetonate [VO(acac)2] as the catalyst and iodobenzene diacetate as the oxidant. The reaction involves coupling of sp3‐ and sp2‐hybridized carbons and proceeds through the formation of an iminium ion. A wide variety of imidazo[1,2‐a]pyridines were converted to bis(imidazo[1,2‐a]pyridin‐3‐yl)methanes in good to excellent yields. A gram‐scale reaction demonstrated the potential for the scale‐up processes.
An efficient synthesis of (E)‐5‐aryl(halo)methylenebicyclo[2.2.2]oct‐2‐enes is reported. Lewis acid‐promoted carbohalogenation of 4‐(3‐arylprop‐2‐ynyl)‐cyclohex‐2‐enols in dichloromethane proceeds rapidly to afford the exo‐methylene‐bridged bicycles in good yields. This method also provides an easy access to (E)‐5‐aryl(halo)methylenebicyclo[2.2.1]hept‐2‐enes from the five‐membered ring 2,6‐enynols. The reactions are procedurally simple and high yielding, producing the aryl(halo)methylene‐bridged bicycles in minutes under air and mild conditions.
The first active aza analogue of narciclasine was synthesized from a pentasubstituted derivative of nicotinic acid. The key features of the synthesis include a halogen dance of bromopyridine and an intramolecular Heck reaction with a conduramine derived chemoenzymatically from bromobenzene. 10‐Aza‐narciclasine was found to have reasonable activity against several cancer cell lines.
1‐Bromo‐2‐(cyclopropylidenemethyl)benzenes react with 2‐alkynylphenols under palladium catalysis, leading to indeno[1,2‐c]chromenes in moderate to good yields. The molecular complexity and diversity can be introduced efficiently from easily available starting materials.
