Competitive thermal ene reaction and Diels-Alder reactions of 2-[N-(alk-2-enyl)benzylamino]-3-vinylpyrido[1,2-a]pyrimidin-4(4H)-ones

Thermal reaction of 2-[N-(alk-2-enyl)benzylamino]-3-(2-substituted and 2,2-disubstituted)vinylpyrido[1,2-a]pyrimidin-4(4H)-ones gave azepine, the desired ene products, and/or pyran derivatives. The formation of the latter was responsible for the [4+2] cycloaddition reaction between the α,β-unsaturated ester carbonyl moiety as a diene part and the alkenylamino moiety as an ene one. The reaction features depended upon the kinds of substituents both on the vinyl and alkenyl counterparts; strongly electron-withdrawing substituents on the vinyl moiety or an electron-donating substituent on the alkenyl one changed the reaction feature from the ene reaction to the hetero Diels-Alder reaction.     

Recent advances in ionic liquids: green unconventional solvents of this century: part II

Abstract

In the second part of our paper, further recent developments of ionic liquids in selected name reactions of carbonyl chemistry such as Mannich, Reformatsky, Cannizaro, Streacker, Barbier, Pechmann, etc. are described.     

Palladium bis(2,2,6,6-tetramethyl-3,5-heptanedionate) catalyzed Suzuki, Heck, Sonogashira, and cyanation reactions

Palladium bis(2,2,6,6-tetramethyl-3,5-heptanedionate): a structurally well-defined O-containing transition metal complex is reported as an efficient catalyst for Suzuki, Heck, and Sonogashira cross-coupling reactions. The protocol was also applied successfully for cyanation of aryl halides under milder operating conditions. The system tolerated the coupling of various aryl halides with alkenes, alkynes, and organoboronic acid along with the cyanation of aryl halides providing good to excellent yields of desired products.     

One-pot and regioselective synthesis of polysubstituted 3,4-dihydroquinazolines and 4,5-dihydro-3H-1,4-benzodiazepin-3-ones by sequential Ugi/Staudinger/aza-Wittig reaction

An efficient one-pot and regioselective synthesis of 3,4-dihydroquinazolines and 4,5-dihydro-3H-1,4-benzodiazepin-3-ones by Ugi/Staudinger/aza-Wittig sequence has been developed. The Ugi reactions of 2-azidobenzylamines, aldehydes, acids (or α-keto acids) and isocyanides produced the azide intermediates, which were then treated with tributylphosphine or triphenylphosphine to give polysubstituted 3,4-dihydroquinazolines or 4,5-dihydro-3H-1,4-benzodiazepin-3-ones in moderate to good yields by tandem Standinger/aza-Wittig reactions.     

Preparation of α- or β-trifluoromethylated vinylstannanes and their cross-coupling reactions

α- or β-Trifluoromethylated vinylstannanes 1, 2a, 3 and 4 were prepared form 1,1-bis(phenylthio)-2,2,3,3,3-pentafluoropropylbenzene (5) via several steps. The cross-coupling arylation reactions of 1–4 with aryl iodides bearing a bromo, methoxy, methyl, nitro or trifluoromethyl group on para- or meta-position of benzene ring afforded the corresponding coupling products in good yields. Compounds 1, 2a and 4 underwent the acylation reaction with various types of acyl chlorides to give the corresponding trifluoromethylated enone derivatives in good yields. Reduction of trifluoromethylated enone derivatives with LiAlH₄, followed by Fridel-Craft’s type of cyclization with AlCl₃ provided trifluoromethylated indene derivatives in good yields.     

A Manifold Three‐Step Synthetic Route to Polycyclic Annulated Hydantoins via Cyclic Imines

A new three‐step synthetic pathway to generate polycyclic annulated hydantoins via rarely investigated heterocyclic imines is described. This procedure includes a one‐pot reaction forming imines as precursor structures (e.g., Asinger reaction), followed by an Ugi reaction to build up a bisamide structure that allows a ring‐closing reaction to the targeted hydantoins via substitution. This pathway leads to a multiplicity of substances with a potential pharmacological activity.     

Oxidative addition of N-halosuccinimides to palladium(0): the discovery of neutral palladium(II) imidate complexes, which enhance Stille coupling of allylic and benzylic halides

The Stille coupling of organostannanes and organohalides, mediated by air and moisture stable palladium(II) phosphine complexes containing succinimide or phthalimide (imidate) ligands, has been investigated. An efficient synthetic route to several palladium(II) complexes containing succinimide and phthalimide ligands, has been developed. cis-Bromobis(triphenylphosphine)(N-succinimide)palladium(II) [(Ph₃P)₂Pd(N-Succ)Br] is shown to mediate the Stille coupling of allylic and benzylic halides with alkenyl, aryl and allyl stannanes. In competition experiments between 4-nitrobromobenzene and benzyl bromide with a cis-stannylvinyl ester, (Ph₃P)₂Pd(N-Succ)Br preferentially cross-couples benzyl bromide, whereas with other commonly employed precatalysts 4-nitrobromobenzene undergoes preferential cross-coupling. Furthermore, preferential reaction of deactivated benzyl bromides over activated benzyl bromides is observed for the first time. The type of halide and presence of a succinimide ligand are essential for effective Stille coupling. The type of phosphine ligand is also shown to alter the catalytic activity of palladium(II) succinimide complexes.     

Extension of solution‐reaction‐surface description to examination of nonequilibrium solvation effect for microsolvated reaction

A microscopic method to examine a nonequilibrium solvation effect is reported. The solution reaction is simplified as a barrier‐crossing reaction within a solution reaction surface that corresponds to a two‐dimensional space determined by solute and solvent reactive coordinates. For this simplification, the motions within the space spanned by nonreactive coordinates are frozen. We derive three rate constant expressions: (1) in the nonadiabatic solvation limit, (2) in the equilibrium solvation limit, and (3) of the transition‐state theory. This method was applied to the examination of the contact‐ion‐pair formation of t‐BuCl in four waters. We found that the nonadiabatic solvation picture overestimates the nonequilibrium solvation effect. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 791–796, 2000     

Sulfilimine palladacycles: stable and efficient catalysts for carbon-carbon coupling reactions

A new family of sulfilimine-based palladacycles (1-4) has been synthesized in high yields from easily accessible starting materials and is found to exhibit high catalytic activities for carbon-carbon bond-formation in Suzuki, Heck, Sonogashira and Ullmann-type reactions, affording coupled products in excellent yields.     

Mono-Gold(I)-Catalyzed Enantioselective Intermolecular Reaction of Ynones with Styrenes: Tandem Diels–Alder and Ene Sequence

Gold-catalyzed intermolecular reaction leading to dihydronaphthalene derivatives in one pot from two equivalents of ynones with respect to styrene is uncovered. The [4+2] Diels–Alder cycloaddition of ynones and styrenes is catalyzed by a mono-gold(I) complex and the conjugated acid to provide an unstable 3,8a-dihydronaphthalene to subsequently undergo an intermolecular ene-type reaction with the π-activated ynone to afford multi-component coupling dihydronaphthalene products. Linear relationships between chiral ligand-gold complexes and chiral dihydronaphthalene products proves mono-gold catalysis that triggers an asymmetric tandem Diels–Alder and ene reaction sequence.     

Di(2-pyridyl)methylamine-palladium dichloride complex covalently anchored to a styrene-maleic anhydride co-polymer as recoverable catalyst for C-C cross-coupling reactions in water

A new polymer-supported di(2-pyridyl)methylamine-palladium dichloride complex covalently anchored to a styrene-alt-maleic anhydride co-polymer is prepared. This complex catalyzes Heck, Suzuki and Sonogashira cross-coupling reactions in neat water with similar efficiency than the monomeric complex. The turnover number (TON) of this polymer reaches up to 10⁴ for Heck reactions, whereas for Suzuki and Sonogashira couplings TONs up to 10⁵ are achieved. There is low leaching of palladium after filtration of the polymer and the activity remains almost constant after fourth and five reaction cycles especially in Sonogashira reactions. In the case of the Suzuki reaction Pd nanoparticles are dispersed into the polymer after the first cycle according to TEM images and 2.4% of Pd are found by ICP-OES in the corresponding filtrate. Alternatively, these palladium-catalyzed reactions can also be performed under microwave heating. These couplings take place with better efficiency with polymer-supported di(2-pyridyl)methylamine-palladium dichloride complex than with the polyurea-encapsulated Pd EnCat™ 40.     

A DFT study on a mutipathways,one product reaction: Initially divergent radical reactions reconverge to form a single product

The mechanism for initially divergent radical reactions reconverging to form a single product is studied using density functional theory calculations. The calculation results suggest that there are six possible pathways from reactants to products. The free energy barriers of the rate‐determining steps of each pathway are almost equal. Thus, different from usual reaction, the selectivity of this reaction is determined by the relative value of free energy barriers of the two competitive reactions, that is, cyclization and bimolecular trapping, rather than that of rate‐determining steps. In all reaction pathways, cyclization reaction is more competitive than bimolecular trapping reaction due to its low free energy barrier. In addition, the free energy barriers of bimolecular trapping reaction between Bu₃SnH and reactants are all lower than that of NC? C₆H₁₁. However, Bu₃SnH is not always suitable due to its large steric repulsion. © 2014 Wiley Periodicals, Inc.     

Stereoselective oxidative addition of benzenethiol to idene in the presence of ovoalbumin

The oxidative addition of benzenethiol to indene in the presence of ovoalbumin produces only one isomer on the surface of the protein,trans-anti-2-phenylsulfinyl-1-indanol. This reaction may be considered as a biomimetic model of detoxification of certain hydrocarbons by the liver.

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Stereoselektive oxydative Anlagerung von Thiophenol an Inden in Gegenwart von Ovoalbumin (Kurze Mitteilung)

Zusammenfassung Durch die oxydative Anlagerung von Thiophenol an Inden in Gegenwart von Ovoalbumin bildet sich nur ein Isomer an der Oberfläche des Proteins, dastrans-anti-2-Phenylsulfinyl-1-Indanol. Diese Reaktion kann als ein biomimetisches Modell der Entgiftung von gewissen Kohlenwasserstoffen durch die Leber betrachtet werden.

     

Development of an unexpected reaction pathway for the synthesis of 1,2,4-trisubstituted pyrrolo[1,2-a]quinoxalines through palladium-catalyzed cascade reactions

1,2,4-trisubstituted pyrrolo[1,2-a]quinoxalines are synthesized through the multi-component reaction of 3-substituted 2-chloroquinoxalines, propargyl bromide, and excess secondary amines in the presence of a palladium copper catalytic system. This one-pot process provides an unexpected synthesis of new trisubstituted pyrrolo[1,2-a]quinoxalines by the introduction of two amine substituents onto the fused pyrrole rings in a single reaction procedure. The compounds formed are fully characterized by the analytical spectral data and X-ray analysis. A number of synthesized pyrrolo[1,2-a]quinoxaline derivatives are also screened against the three bacterial strains Micrococcus luteus, Pseudomonas aeruginos, and Bacillus subtilis. According to the results obtained, compounds 3b, 3c, and 3e are active against M. luteus, compounds 3b and 3e are active against Ps. Aeruginos, and only compound 3f is active against all the three bacterial strains.     

One‐Pot Wittig Reactions in Aqueous Media: A Rapid and Environmentally Benign Synthesis of α,β‐Unsaturated Carboxylic Esters and Nitriles

One‐pot Wittig reactions of ethyl bromoacetate and bromoacetonitrile with aldehydes in the presence of PPh₃ and LiOH in water were investigated. Most of the olefination reactions completed within 5–120 min in refluxing water containing 1.2 M LiCl to afford the olefin products in 71–97% yields with 100:0–55:45 ratios of E:Z isomers.     

An enantioselective organocatalyzed aza-MBH domino process: application to the facile synthesis of tetrahydropyridines

A chiral acid-base organocatalyst was found to promote an aza-MBH domino process between α,β-unsaturated carbonyl compounds and N-tosylimines to afford tetrahydropyridine derivatives with high enantioselectivity.     

Ethylcyclopentane ring opening reaction over PtGe/Al2O3 catalysts prepared by controlled surface reaction

Platinum-germanium catalysts supported on a non-acidic Al₂O₃ have been prepared by adding Ge in amounts corresponding nominally to 1/8 (PtGe1/8/Al₂O₃); 1/2 (PtGe1/2/Al₂O₃); 1 (PtGe1/Al₂O₃) and 2 (PtGe2/Al₂O₃) monolayers by controlled surface reaction of Ge(n-C₄H₉)₄ to Pt/Al₂O₃. These catalysts were characterized by electron microscopy (TEM), FTIR of CO adsorption and H₂ chemisorption. The ring opening of ethylcyclopentane (ECP) was studied as a test reaction between 543 and 633 K. PtGe1/8/Al₂O₃ catalyst produced the most ring opening products (ROP) in the whole temperature range. A good agreement with statistical values of ROP was observed at low temperature, but at higher temperature, the opening became selective, producing mostly heptane. Bimetallic catalysts PtGe1/Al₂O₃ and PtGe2/Al₂O₃ led to a nonselective hydrogenolysis, similar to the monometallic platinum catalyst Pt/Al₂O₃. The catalysts PtGe1/Al₂O₃ and PtGe2/Al₂O₃ produced ROP with the lowest selectivity; instead, much aromatics and fragments were formed, in increasing amounts above 600 K.     

Synthesis of substituted biaryls via Suzuki,Stille and Hiyama cross‐coupling and homo‐coupling reactions by CN‐dimeric and monomeric ortho‐palladated catalysts

The catalytic activity of dimeric [Pd{C₆H₂(CH₂CH₂NH₂)–(OMe)₂,2,3}(μ‐Br)]₂ and monomeric [Pd{C₆H₂(CH₂CH₂NH₂)–(OMe)₂,2,3}Br(PPh₃)] complexes as efficient, stable and air‐ and moisture‐tolerant catalysts was investigated in the Suzuki, Stille and Hiyama cross‐coupling and homo‐coupling reactions of various aryl halides. Substituted biaryls were produced in excellent yields in short reaction times using catalytic amounts of these complexes. The monomeric complex was demonstrated to be more active than the corresponding dimeric catalyst for the cross‐coupling reaction of unreactive aryl bromides and chlorides. The combination of homogeneous metal catalysts and microwave irradiation gave higher yields of products in shorter reaction times. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of allyl phosphine oxides/boranes via Horner reaction of bis(diphenylphosphine)ethane monoxide reagent with an aldehyde

The Horner-Wittig addition-elimination reaction using bis(diphenylphosphine)ethane monoxide [DIPHOS(O)] with an aldehyde affords Z-allyl phosphine oxides/boranes. Alternatively, the stereoselective Lewis acid mediated intermolecular reduction of its γ-ketobisphosphoranes and stereoselective intramolecular reduction of γ-ketophosphine·borane derivatives followed by elimination of diphenylphosphinate affords E-allyl phosphine oxides/boranes with good to high selectivity. Allyl phosphine oxides are common intermediates in the synthesis of polyenes.     

Evidence of Kinetically Relevant Consistency in Thermal and Photo-Thermal HCOOH Decomposition over Pd/LaCrO3/C3N4 Composite

Photo-thermal catalysis has been an attractive alternative strategy to promote chemical reactions for years, however, how light cooperates with thermal energy is still unclear. We meet this demand by exploring reaction mechanism via pressure dependency studies as well as H/D exchange experiments with HCOOH decomposition as a probe over a palladium nanoparticle (Pd_n) and isolated Pd (Pd₁) decorated LaCrO₃/C₃N₄ composite catalyst, in which the H₂ formation rate shows a first-order dependence on HCOOH and inverse first-order dependence on CO partial pressures no matter the reaction was driven by thermal or photo-thermal energy. Additionally, negligible kinetic isotopic effects (KIEs: k_H/k_D) were determined under both dark and light conditions at 1.04 and 1.18 when the HCOOH was replaced by HCOOD. Besides, when the reactant HCOOH was further replaced by DCOOD, the KIE values of 1.55 (dark) and 1.92 (light) were obtained, which indicates that the HCOOH decomposition follows kinetically relevant (KR) of C−H bond rupture within HCOOH molecule under both thermal and photo-thermal reaction conditions and the catalytic surface was found to be densely covered by CO based on the pressure dependency studies as well as the in situ Fourier transform infrared spectroscopy (FTIR) analysis. Clearly, the HCOOH decomposition driven by thermal and photo-thermal energy follows the same reaction mechanism. Nevertheless, light induced hot electrons and the derived thermal effect do cause the enhancement of the reaction activity in some circumstances compared with bare thermal catalysis, which clarifies the confusion on cooperation mechanism of photo and thermal energies from the kinetic perspective. Hot electrons induced by photo-illumination was confirmed by in situ FTIR CO chemisorption with ∼10 cm⁻¹ redshift identified of the CO feature once light was introduced. Meanwhile, the photo thermal reaction system suffers from severe electron-hole re-combination at high reaction temperatures and make the thermal effect of photo irradiation dominant with respect to the effect at low reaction temperatures. This research provides insight to the mechanism on how photo-thermal reaction works and draws attention to the photo-thermal reaction process in boosting catalytic activity.