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%).
For the asymmetric hydrophosphonylation of aldehydes, an efficient organocatalytic approach with a diaminomethylenemalononitrile‐based hydrogen‐bonding donor catalyst is presented. The catalyst induces high yields and excellent enantioselectivities (up to 98% yield, 96% ee).
An efficient synthesis of indazoles from readily accessible E/Z mixtures of o‐haloaryl N‐tosylhydrazones has been developed. The thermo‐induced isomerization of N‐tosylhydrazones is discussed. A series of valuable indazole derivatives are prepared in good yields, and the method has been successfully applied to the synthesis of the bioactive compounds, lonidamine, AF‐2785, axitinib, YC‐1 and YD‐3.
The synthesis of chiral bidentate bisphosphonite ligands based on the TADDOL motif from readily available starting materials has been developed. Taking advantage of the modular nature of the building blocks, a diverse ligand library has been prepared. Their catalytic potential has been evaluated in the asymmetric hydroformylation of styrene and derivatives. These catalysts showed high activity and provided the aldehydes in high enantiomeric purity.
A comparison of the relative catalytic efficiencies of Lewis‐basic amines vs. N‐oxides for the acylation, sulfonylation and silylation of primary, secondary and tertiary alcohols is reported. Whilst the amines are generally superior to the N‐oxides for acylation, the N‐oxides are superior for sulfonylation and silylation. In particular, 1‐methylimidazole N‐oxide (NMI‐O) is found to be a highly efficient catalyst for sulfonylation and silylation reactions. To the best of our knowledge, NMI‐O is the first amine or N‐oxide Lewis basic organocatalyst capable of promoting the efficient silylation of tert‐alcohols in high yield with low catalyst loading under mild reaction conditions.
A chemoselective reduction of α‐keto amides to biologically important α‐hydroxy amides (mandelamides) by polymethylhydrosiloxane (PMHS) using 5 mol% potassium phosphate (K3PO4) as catalyst has been developed. This transition metal‐free protocol discloses excellent chemoselectivity for the ketone reduction of α‐keto amides in the presence of other reducible functionalities like ketone, nitro, halides, nitrile and amide. Also, the chemoselectively reduced α‐hydroxy amide has been derivatized to isocyanide‐free Passerini adducts. The N‐alkyl‐α‐hydroxy amides have been successfully converted to 3‐phenyloxindole derivatives by treatment with methanesulfonyl cholride and triethylamine.
10% Palladium on carbon (10% Pd/C) successfully catalyzed the intramolecular C−H amination of various N‐mesylated 2‐aminobiphenyls in the presence of a catalytic amount of pyridine N‐oxide in heated dimethyl sulfoxide (DMSO) under an oxygen atmosphere to afford the corresponding N‐mesylcarbazoles. The reaction would proceed via a single‐electron transfer process based on its significant suppression by the addition of a single‐electron scavenger, tetracyanoquinodimethane (TCNQ), and the substituents on the aromatic rings of the substrate have an insignificant effect on the reaction progress.
Polyfunctional molecules, 1,5‐enynes, have been achieved via a palladium(0)‐catalyzed domino coupling reaction of (Z)‐β‐bromostyrenes with norbornenes in the presence of cesium carbonate and N,N‐dimethylformamide. The process involves a double Heck‐type procedure, two‐fold C(sp2) H activation and formation of two carbon‐carbon bonds. There are possibilities of diversified transformation for the domino coupling of (Z)‐β‐bromostyrenes with norbornenes, the procedure is successfully driven to 1,5‐enynes via accurate adjustment of the reaction conditions.
A straightforward approach for the chemodivergent synthesis of quinolines is described through site‐selective coupling of ortho‐aminoaryl ketones with α‐enolic dithioesters (DTEs) under solvent‐free conditions. The operationally and user‐simple one‐pot methodology is based on the trifunctional nature of DTEs. Both the carbonyl and the thiocarbonyl moiety in α‐enolic dithioesters were employed for the efficient construction of three differently substituted quinolines in a chemoselective manner simply by variation of an easy to handle acid catalyst.
Gold carbenes generated via 1,2‐migration of a propargylic ester group can be transferred over a tethered alkyne. The use of aromatic backbones leads after a 1,7‐carbene transfer to a benzyl‐stabilized carbene as intermediate. A 1,2‐shift of a methyl group delivers vinyl‐substituted β‐naphthol derivatives as the final products.
The reaction of N‐[2.2]paracyclophanyl‐substituted amides or amines with phenyliodine diacetate (PIDA) and protic nucleophiles affords mixed para‐substituted [2.2]paracyclophane derivatives in moderate to good yields. As protic nucleophiles carboxylic acids and alcohols as well as pyridine hydrobromide can be used. 4‐Hydroxy[2.2]paracyclophane reacts in an analogous manner.
An efficient regioselective fluorotrifluoromethylation of unactivated alkenes has been developed. The reaction of alkenes with (trifluoromethyl)trimethylsilane (TMSCF3) and Selectfluor in the presence of silver trifluoromethanesulfonate (AgOTf), cesium fluoride (CsF), and iodobenzene diacetate [PhI(OAc)2] in N,N‐dimethylformamide (DMF) at −20 °C gave the corresponding fluorotrifluoromethylated products in moderate to good yields. The silver salt turns out to be crucial for this transformation.
Dehydrogenative coupling of primary alcohols with secondary amines to form tertiary amides and dihydrogen (H2) is efficiently catalyzed by bipyridyl‐based ruthenium pincer complexes (0.2–1 mol%) under neutral conditions (in case of the dearomatized complexes), or with added catalytic amount of base. The reaction is sensitive to steric hindrance; in the case of amidation of bulky secondary amines a less sterically hindered complex is more efficient. Selective acylation of primary amines in the presence of secondary amines was also demonstrated.
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.
Catalytic asymmetric reduction of N‐unsubstituted β‐enamino esters represents a major challenge for asymmetric catalysis. In this paper, the first organocatalytic system that could be used for the asymmetric hydrosilylation of N‐unsubstituted β‐enamino esters has been developed. Using N‐tert‐butylsulfinyl‐L ‐proline‐derived amides and L ‐pipecolinic acid‐derived formamides as catalyst, a broad range of β‐aryl‐ and β‐alkyl‐substituted free β‐amino esters could be prepared with high yields and enantioselectivities. The practicality was illustrated by the gram‐scale asymmetric synthesis of ethyl (R)‐3‐amino‐3‐phenylpropanoate and isopropyl (S)‐3‐amino‐4‐(2,3,5‐trifluorophenyl)butanoate. The resulting product can be smoothly transformed to the FDA approved medicines dapoxetine and sitagliptin in a short synthetic route.
An efficient alkylation method of functionalized alkyl halides under mild nickel‐catalyzed C(sp3) C(sp2) Suzuki cross‐coupling conditions is described. The features of this approach are excellent functional group compatibility, low cost nickel catalyst, and the use of a mild base. This is also the first successful example of the nickel‐catalyzed direct 2,2‐difluoroethylation or 2,2,2‐trifluoroethylation of aryl‐/heteroarylboronic acids.
A copper‐mediated, chelation‐assisted ortho C H bond nitration of benzoic acid derivatives using sodium nitrite as the source of the nitro group has been achieved with the aid of an 8‐aminoquinoline directing group. Selective mono‐ or dinitration can be achieved by simply changing the reaction conditions. The method shows excellent functional group tolerance and provides a novel and straightforward route for the preparation of ortho‐nitrated benzoic acids.
A highly efficient palladium‐catalyzed decarbonylative dehydration reaction of carboxylic acids is reported. This method transforms abundant and renewable even‐numbered natural fatty acids into valuable and expensive odd‐numbered alpha olefins. Additionally, the chemistry displays a high functional group tolerance. The process employs a low loading of palladium catalyst and proceeds under solvent‐free and relatively mild conditions.
An efficient, green and first catalytic process has been developed for the direct synthesis of amides from readily available petroleum by‐products (methylarenes) and amines using an iron catalyst. In this new catalytic reaction, the methyl group of the methylarene is oxidized to the corresponding aldehyde through non‐directed C H oxidation followed by its oxidative amidation with N‐chloroamine, yielding the carboxylic amide. Oxidation with an iron catalyst, tert‐butyl hydroperoxide (TBHP) as sole oxidant, the synthesis of amides under mild reaction conditions and the utilization of methylarenes as starting material make this methodology novel and environmentally benign.
An intermolecular radical cascade reaction between readily prepared o‐methylthio‐arylamines or o‐methylselanyl‐arylamines and alkynes for the preparation of valuable benzothiophenes or benzoselenophenes is reported. These transformations occur efficiently with complete regioselectivity and the products are obtained in moderate to good yields. The current protocol is successfully applied to the synthesis of the key intermediates of the drug raloxifene and an AT1 receptor antagonist.
