Gold‐ and Silver‐Catalyzed Intramolecular Hydroamination of Terminal Alkynes: Water‐Triggered Chemo‐ and Regioselective Synthesis of Fused Tricyclic Xanthines

A simple, convenient and green synthetic approach to diverse fused tricyclic xanthines has been developed via gold(I) complex‐catalyzed intramolecular hydroamination or silver(I)‐catalyzed isomerization‐hydroamination of terminal alkynes under microwave irradiation in water. The first synthesis of N9‐annelated xanthines has also been reported.     

Gold(I)‐Catalyzed Intramolecular Hydroamination of N‐Allylic N′‐Arylureas to form Imidazolidin‐2‐ones

Treatment of N‐allylic N′‐arylureas with a catalytic 1:1 mixture of di‐tert‐butyl‐o‐biphenylphoshphine gold(I) chloride and silver hexafluorophosphate (1 mol%) in chloroform at room temperature led to 5‐exo‐hydroamination to form the corresponding imidazolidin‐2‐ones in excellent yield. In the case of N‐allylic ureas that possessed an allylic alkyl, benzyloxymethyl, or acetoxymethyl substituent, gold(I)‐catalyzed 5‐exo‐hydroamination leads to formation of the corresponding trans‐3,4‐disubstituted imidazolidin‐2‐ones in excellent yield with ≥50:1 diastereoselectivity.     

Cationic Gold‐ and Silver‐Catalyzed Cycloisomerizations of Propargylic Ureas: A Selective Entry to Oxazolidin‐2‐imines and Imidazolidin‐2‐ones

A comparative study on transition metal‐catalyzed cycloisomerizations of propargylic ureas derived in situ from secondary propargylic amines and tosyl isocyanate was performed. The influence of catalytic system on the reaction outcome was thoroughly studied on two model examples resulting in the establishment of two selective protocols for both O‐ and N‐cyclizations. The application of cationic gold(I) catalysis generally resulted in a formation of oxazolidin‐2‐imines as major products while the application of silver(I) triflate selectively provided the corresponding imidazolidin‐2‐ones. An attempt to rationalize the observed chemoselectivity is described. The scope of both processes was demonstrated through the use of variously substituted secondary propargylic amines.     

Zinc(II) Triflate‐Catalyzed Divergent Synthesis of Polyfunctionalized Pyrroles

The zinc(II) triflate‐catalyzed synthesis of highly functionalized pyrroles is described. The sequence involves the preliminary preparation of α‐aminohydrazones by Michael addition of primary amines to 1,2‐diaza‐1,3‐dienes. The treatment of these intermediates with dialkyl acetylenedicarboxylates produces α‐(N‐enamino)‐hydrazones that are converted into the corresponding pyrroles. The substituents on the carbon in position four of 1,2‐diaza‐1,3‐dienes drive the regioselectivity of the ring closure process. Starting from 4‐aminocarbonyl‐1,2‐diaza‐1,3‐dienes only dialkyl 1‐substituted 5‐aminocarbonyl‐1H‐pyrrole‐2,3‐dicarboxylates are achieved by Lewis acid‐catalyzed ring closure. A screening of several Lewis/Brønsted acid catalysts is performed. Zinc(II) triflate is the most efficient catalyst. Under similar reaction conditions, employing 4‐alkoxycarbonyl‐1,2‐diaza‐1,3‐dienes, only 4‐hydroxy‐1H‐pyrrole‐2,3‐dicarboxylates are synthesized. These latter reactions can be accomplished regioselectively also in one pot. Using 4‐aminocarbonyl‐1,2‐diaza‐1,3‐dienes, diamines and dialkyl acetylenedicarboxylates the sequence provides the corresponding α,ω‐di(N‐pyrrolyl)alkanes.     

Gold(I)‐ and Brønsted Acid‐Catalyzed Ring‐Opening of Unactivated Vinylcyclopropanes with Sulfonamides

The gold(I)‐ or Brønsted acid‐catalyzed reaction of unactivated vinylcyclopropanes (VCPs) with sulfonamides affords useful homoallylic amine derivatives. This ring‐opening reaction occurs in a highly selective manner affording in the case of α‐phenyl‐substituted VCPs products with the E‐configuration exclusively.     

Transition Metal‐Catalyzed Synthesis of (E)‐2‐(Alkylthio)alka‐1,3‐dienes from Allenes and Dialkyl Disulfides with Concomitant Hydride Transfer

Reaction of dialkyl disulfides or diselenides with allenes is catalyzed by a rhodium‐phosphine complex and trifluoromethanesulfonic acid giving (E)‐2‐alkylthio(seleno)‐1,3‐dienes and (E)‐2‐alkylthio(seleno)‐2‐alkenes. Unlike the reaction of alkynes, the reaction of allene is accompanied by hydride transfer.     

Enantioselective Carbonyl‐Ene Reactions of Arylglyoxals with a Chiral Palladium(II)‐BINAP Catalyst

The palladium(II)‐BINAP‐catalyzed enantioselective carbonyl‐ene reactions between ten arylglyoxals and five alkenes were systematically investigated and demonstrated good to excellent enantioselectivities with high ee values of up to 93.8 %. The results showed that both arylglyoxals and alkenes exert evident effects on the enantioselectivity. Particularly, the ortho‐methyl substituents of the substrates could increase the enantioselectivity. The achieved excellent enantioselectivities may be due to the corresponding substrate matches well fitting the chiral space created by the chiral palladium(II)‐BINAP catalyst. The ortho‐methyl substituents may improve the fitting of the substrate match to the chiral space created by the chiral catalyst, hence the enantioselectivity is improved. When using dienes (1,4‐diisopropenylbenzene and 1,3‐diisopropenylbenzene) as substrates in this reaction, only one of the two carbon‐carbon double bonds participated into the reaction affording tetrafunctional organic compounds with moderate enantioselectivities of up to 83.8 % ee. The chiral Lewis acid palladium(II) catalyst incorporating (R)‐BINAP, which is a conformationally restricted chiral ligand, is very stable in ionic liquids and could be recycled 21 times with retention of the high enantioselectivity.     

Microwave‐Assisted Synthesis of Pyrazino[2,1‐b]quinazolines and 3‐Indolyl‐2(1H)‐pyrazinones Employing a Chemoselective Silver(I)‐ and Gold(I)‐Catalyzed Reaction

Novel microwave‐assisted syntheses of pyrazino[2,1‐b]quinazolines and 3‐indolyl‐2(1H)‐pyrazinones employing silver(I)‐ or gold(I)‐catalyzed protocols have been elaborated. The scope and limitations of these processes have been investigated.     

Practical Synthesis of Allylic Silanes from Allylic Esters and Carbamates by Stereoselective Copper‐Catalyzed Allylic Substitution Reactions

The first copper‐catalyzed allylic substitution reactions of allylic acetates and carbamates employing a bis(triorganosilyl)zinc reagent are reported. This novel procedure avoids the use of stoichiometric amounts of copper salts which are usually mandatory with this chemistry. Application of this methodology to standard model substrates substantiates a high diastereoselectivity for the double bond geometry (E : Z) as well as the relative configuration (syn : anti).     

Simple Chiral Diaminobinaphthyl Dilithium Salts for Intramolecular Catalytic Asymmetric Hydroamination of Amino‐1,3‐dienes

Simple and easily accessible chiral lithium amide salts are reported as efficient (pre)catalysts for the diastereo‐ [up to (E:Z)=92:8] and enantioselective [up to 72% ee (E)] hydroamination/cyclisation of conjugated primary aminodienes. These chiral lithium salts are straightforwardly prepared by in situ combination of an N‐substituted (R)‐(+)‐1,1′‐binaphthyl‐2,2′‐diamine ligand and a commercial methyllithium solution. Information on the solid‐state structure of these salts was obtained by X‐ray analysis of a single crystal.     

On the Trapping of Vinylgold Intermediates

An internal aryl‐substituted ortho‐alkynylphenol and a similar aniline with stoichiometric amounts of N,N′‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene‐gold tosylate [(IPr)AuOTs] and triethylamine gave the aurated heterocycles as stable intermediates of the corresponding gold(I)‐catalysed hydrooxylation and hydroamination reactions. X‐ray crystal structure analyses of both products could be obtained. A similar internal alkyl‐substituted ortho‐alkynylphenol gave only the cycloisomerised product, no aurated intermediate could be detected.     

Binaphthol‐Based Diphosphite Ligands in Asymmetric Nickel‐Catalyzed Hydrocyanation of Styrene and 1,3‐Cyclohexadiene: Influence of Steric Properties

A series of chiral (R)‐binaphthol‐based diphosphite ligands with different substituents was prepared and applied in the asymmetric nickel‐catalyzed hydrocyanation of styrene and 1,3‐cyclohexadiene to investigate the influence of their steric properties. The optimum steric properties for the hydrocyanation reaction lie within a narrow window. With the optimized ligand, hydrocyanation of styrene gave full conversion (Subs/Ni=100) with 49 % ee, the TON was determined to be 600. Hydrocyanation of 1,3‐cyclohexadiene gave 50 % conversion (Subs/Ni=500) with an excellent ee of 86 %. This demonstrates that high ees are not only accessible for vinylarenes but also for conjugated dienes in the asymmetric nickel‐catalyzed hydrocyanation.     

One Step Synthesis of Chiral Olefins via Asymmetric Diamination and their Applications as Ligands for Rhodium(I)‐Catalyzed 1,4‐Additions

A variety of acyclic chiral dienes were synthesized in a single step via palladium(0)‐catalyzed asymmetric allylic and homoallylic C H diamination of terminal olefins. The applications of such simple dienes as steering ligands for rhodium(I)‐catalyzed asymmetric 1,4‐additions afforded the corresponding adducts in excellent yields and up to 85% ee.     

Tandem Gold(III)‐Catalyzed Amination‐Intramolecular Hydroamination Reactions of 1‐En‐4‐yn‐3‐ols with Sulfonamides: Efficient Approach to Highly Substituted Pyrroles

A simple, convenient and efficient synthetic approach to highly substituted pyrroles has been developed by utilizing a gold(III)‐catalyzed tandem amination‐intramolecular hydroamination reaction. The first examples of gold‐catalyzed, selective amination of 1‐en‐4‐yn‐3‐ols have also been disclosed.     

Acceleration of Anti‐Markovnikov Hydroamination in the Synthesis of an Active Pharmaceutical Ingredient

Slow chemical reactions are a big challenge in the modern pharmaceutical industry. Their accelerations together with the introduction of continuous manufacturing modes are major drivers for future development. One example reaction is hydroamination, a reaction between unsaturated hydrocarbons and amines. Such a reaction type is the main focus of this work. More precisely, the anti‐Markovnikov hydroamination reaction between cis/trans 9H‐thioxanthene‐2‐chloro‐9‐(2‐propenylidene)‐(9CI) and 1‐(2‐hydroxyethyl)piperazine (HEP) is investigated in detail. It has been traditionally performed in toluene with a huge excess of HEP and reaction times of up to 24 h. Acceleration of the reaction from 24 down to 4 h is achieved by switching from batch operation mode in toluene to either solvent‐free batch mode or microwave‐assisted hydroamination with tetrahydrofuran as a solvent.     

A Novel Assembly of Substituted Pyrroles by Acid‐Catalyzed Sequential Three‐Component Reaction of Amines,Alkynoates, and 1,2‐Diaza‐1,3‐dienes

A novel protocol for the assembly of polysubstituted pyrroles has been developed through the acid‐catalyzed, sequential three‐component reaction of primary aliphatic amines, alkynoates and 1,2‐diaza‐1,3‐dienes (DDs). This methodology proceeds with complete chemo‐/regioselectivity involving first formation of an enamino ester intermediate, in situ Michael addition with azo‐ene compounds and subsequent intramolecular ring closure.     

A Novel Mode of Reactivity for Gold(I): The Decarboxylative Activation of (Hetero)Aromatic Carboxylic Acids

Gold(I) salts are found to mediate the decarboxylation of a variety of aromatic and heteroaromatic carboxylic acids at significatively lower temperatures (as low as 60 °C) than the currently used copper(I) (180–190 °C) and silver(I) (80–140 °C) systems. In contrast to silver(I)‐ and copper(I)‐mediated decarboxylations, the resulting aryl‐gold(I) complexes are stable towards protodemetallation and can be readily isolated.     

On the Gold‐Catalyzed Intramolecular 7‐exo‐trig Hydroamination of Allenes

Aniline derivatives with allene side tethers were tested as substrates for a gold‐catalyzed 7‐exo‐trig hydroamination reaction. The nucleophilicity of the aniline derivatives plays an important role for the outcome of the reaction. While electron‐deficient protecting groups at the nitrogen led to competing pathways like hydroarylation or an allene to diene isomerization, clean formation of the desired benzoxazepines was obtained with unprotected aniline derivatives.     

The Hydroamination of methyl acrylates with amines over zeolites

H-form zeolites, H-FAU and H-BEA have been studied as heterogeneous catalysts for the hydroamination. They catalyzed the reaction of methyl acrylate with aniline to give N-[2-(methoxycarbonyl)ethyl]aniline (1) as a main product. H-BEA and H-FAU zeolites efficiently catalyzed the hydroamination to afford anti-Markovnikov adduct as a main product. The conversion of aniline around 55–85% was achieved within 18 h over H-BEA and H-FAU zeolites with SiO₂/Al₂O₃ molar ratio of 25–30; however, the formation of N,N-bis[2-(methoxycarbonyl)ethyl]aniline (2) as a product of double addition of methyl acrylate to aniline has also been observed as a by-product over H-BEA and H-FAU catalysts. The influences of the reaction parameters such as temperature and catalyst amount, and type of α,β-unsaturated esters and amines have been also investigated.     

Base‐Catalyzed Hydroamination of Olefins: An Environmentally Friendly Route to Amines

The base‐catalyzed hydroamination of olefins offers a simple and elegant access to various primary, secondary, and tertiary amines. Particular focus is placed on developments in the area of hydroamination of non‐activated olefins. Advantages and disadvantages of the methodology compared to other synthetic methods are presented. Special attention is paid to potential industrial applications of this chemistry.