Novel isoxazoline ligand with ferrocene backbone: preparation and application in Heck reaction with water as solvent

Two novel isoxazoline N,N‐bidentate ligands with ferrocene backbone have been synthesized and employed for the palladium‐catalyzed Heck coupling reaction. Among them, 1,3‐bis‐(5‐ferrocenylisoxazoline‐3‐yl)benzene was found to be thermally stable and a highly effective ligand for Heck coupling reaction in neat water without N₂ protection, affording the desired coupling products in good to excellent yield with high diastereoselectivity. The developed catalytic system was also well workable for 1,2‐disubstituted alkenes, which were less involved in the Heck reaction for its larger steric hindrance. Copyright © 2014 John Wiley & Sons, Ltd.     

Palladium‐Catalyzed Annulation of 1,2‐Diborylalkenes and ‐Arenes with 1‐Bromo‐2‐[(Z)‐2‐bromoethenyl]arenes: A Modular Approach to Multisubstituted Naphthalenes and Fused Phenanthrenes

(Z)‐1,2‐Diaryl‐1,2‐bis(pinacolatoboryl)ethenes underwent double‐cross‐coupling reactions with 1‐bromo‐2‐[(Z)‐2‐bromoethenyl]arenes in the presence of [Pd(PPh₃)₄] as a catalyst and 3 M aqueous Cs₂CO₃ as a base in THF at 80 °C. The double‐coupling reaction gave multisubstituted naphthalenes in good to high yields. Annulation of 1,2‐bis(pinacolatoboryl)arenes with bromo(bromoethenyl)arenes in the presence of a catalyst system that consisted of [Pd₂(dba)₃] (dba=dibenzylideneacetone) and 2‐dicyclohexylphosphino‐2′,6′‐dimethoxybiphenyl (SPhos) under the same conditions produced fused phenanthrenes in good to high yields. The first annulation coupling occurred regiospecifically at the bromoethenyl moiety. This procedure is applicable to the facile synthesis of polysubstituted anthracenes, benzothiophenes, and dibenzoanthracenes through a double annulation pathway by using the corresponding dibromobis[(Z)‐2‐bromoethenyl]benzenes as diboryl coupling partners.     

Palladaphosphacyclobutenes as catalysts in Heck and Suzuki reactions

Heck reactions of aryl halides with various olefins and Suzuki reactions of aryl halides with phenylboronic acid catalyzed by palladaphosphacyclobutene have been investigated. The scope of the Heck reaction has been investigated in N,N‐dimethylacetamide at 140 °C using NaOAc as base. Using 0.1% molar ratio of palladaphosphacyclobuyenes, aryl bromides were converted into 1,2‐substitutedethene products in good to high yields through coupling with both vinylarenes and acrylates. Actived aryl chloride reacted with styrene to afford 1,2‐substitutedethene products in moderate yields. The scope of the Suzuki reaction has been conducted in toluene at 110 °C using Cs₂CO₃ as base. Using 0.1% molar ratio of palladaphosphacyclobutene, aryl bromides reacted with phenylboronic acid to afford diaryl derivatives in excellent yield. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of 4‐substituted styrene compounds via palladium catalyzed Suzuki–Miyaura reaction using bidentate Schiff base ligands

Air‐stable symmetric Schiff base have been synthesized and proved to be efficient ligands for Suzuki–Miyaura reaction between aryl bromides and arylboronic acids using PdCl₂(CH₃CN)₂ as palladium source under aerobic conditions. The coupling reaction proceeded smoothly using N,N‐bis(anthracen‐9‐ylmethylene)benzene‐1,2‐diamine (L₇) as ligand to provide 4‐substituted styrene compounds in good yields. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of trans‐Disubstituted Alkenes by Cobalt‐Catalyzed Reductive Coupling of Terminal Alkynes with Activated Alkenes

A cobalt‐catalyzed reductive coupling of terminal alkynes, RC?CH, with activated alkenes, R′CH?CH₂, in the presence of zinc and water to give functionalized trans‐disubstituted alkenes, RCH?CHCH₂CH₂R′, is described. A variety of aromatic terminal alkynes underwent reductive coupling with activated alkenes including enones, acrylates, acrylonitrile, and vinyl sulfones in the presence of a CoCl₂/P(OMe)₃/Zn catalyst system to afford 1,2‐trans‐disubstituted alkenes with high regio‐ and stereoselectivity. Similarly, aliphatic terminal alkynes also efficiently participated in the coupling reaction with acrylates, enones, and vinyl sulfone, in the presence of the CoCl₂/P(OPh)₃/Zn system providing a mixture of 1,2‐trans‐ and 1,1‐disubstituted functionalized terminal alkene products in high yields. The scope of the reaction was also extended by the coupling of 1,3‐enynes and acetylene gas with alkenes. Furthermore, a phosphine‐free cobalt‐catalyzed reductive coupling of terminal alkynes with enones, affording 1,2‐trans‐disubstituted alkenes as the major products in a high regioisomeric ratio, is demonstrated. In the reactions, less expensive and air‐stable cobalt complexes, a mild reducing agent (Zn) and a simple hydrogen source (water) were used. A possible reaction mechanism involving a cobaltacyclopentene as the key intermediate is proposed.     

Monomeric Homoleptic (2‐Pyridylmethyl)(tert‐butyldimethylsilyl)amido Complexes of the Divalent Metals Mg,Mn, Fe,Co, and Zn

The transamination reaction of M[N(SiMe₃)₂]₂ with (2‐pyridylmethyl)(tert‐butyldimethylsilyl)amine yields the corresponding homoleptic metal bis[(2‐pyridylmethyl)(tert‐butyldimethylsilyl)amides] of Mg ( 1 ), Mn ( 2 ), Fe ( 3 ), Co ( 4 ) and Zn ( 5 ). All these compounds crystallize from hexane isotypic in the space group C2/c. From toluene the zinc derivative precipitates as toluene solvate 5 ·toluene. The molecular structures of these compounds are very similar with large NMN angles to the amide nitrogen atoms with NMN values of 148° ( 1 ) and 150° ( 5 ) for the diamagnetic compounds and 156° for the paramagnetic derivatives 2 and 3 . The Co derivative 4 displays a rather small NCoN angle of 142°. Different synthetic routes have been explored for compound 3 which is also available via the metallation reaction of bis(2,4,6‐trimethylphenyl)iron with (2‐pyridylmethyl)(tert‐butyldimethylsilyl)amine and via the metathesis reaction of lithium (2‐pyridylmethyl)(tert‐butyldimethylsilyl)amide with [(thf)₂FeCl₂]. In course of the metathesis reaction, an equimolar amount of lithium (2‐pyridylmethyl)(tert‐butyldimethylsilyl)amide and [(thf)₂FeCl₂] yields heteroleptic (2‐pyridylmethyl)(tert‐butyldimethylsilyl)amido iron(II) chloride ( 6 ) which crystallizes as a centrosymmetric dimeric molecule. The oxidative C‐C coupling reaction of 5 with Sn[N(SiMe₃)₂]₂ leads to the formation of tin(II) 1,2‐bis(2‐pyridyl)‐1,2‐bis(tert‐butyldimethylsilylamido)ethane, tin metal and Zn[N(SiMe₃)₂]₂.     

Vertically π‐Expanded Imidazo[1,2‐a]pyridine: The Missing Link of the Puzzle

The dehydrogenative coupling of imidazo[1,2‐a]pyridine derivative has been achieved for the first time. In cases in which the most‐electron‐rich position of the electron‐excessive heterocycle was blocked by a naphthalen‐1‐yl substituent, neither oxidative aromatic coupling nor reaction under Scholl conditions enabled the fusion of the rings. The only method that converted the substrate into the corresponding imidazo[5,1,2‐de]naphtho[1,8‐ab]quinolizine was coupling in the presence of potassium in anhydrous toluene. Moreover, we discovered new, excellent conditions for this anion‐radical coupling reaction, which employed dry O₂ from the start in the reaction mixture. This method afforded vertically fused imidazo[1,2‐a]pyridine in 63 % yield. Interestingly, whereas the fluorescence quantum yield (Φ_fl) of compound 3 , despite the freedom of rotation, was close to 50 %, the Φ_fl value of flat naphthalene‐imidazo[1,2‐a]pyridine was only 5 %. Detailed analysis of this compound by using DFT calculations and a low‐temperature Shpol′skii matrix revealed phosphorescence emission, thus indicating that efficient intersystem‐crossing from the lowest‐excited S₁ level to the triplet manifold was the competing process with fluorescence.     

Lewis Acid Catalyzed Synthesis of 1‐Aryl‐1,2‐dihydro‐naphtho[1,2‐e][1,3]oxazin‐3‐ones under Solvent Free Conditions: A Mechanistic Approach

Lewis acids catalyzed highly efficient one‐pot three component coupling of β‐naphthol, benzaldehydes and urea to produce 1‐aryl‐1,2‐dihydro‐naphtho[1,2‐e][1,3]oxazin‐3‐one derivatives under solvent free conditions is described. Mechanistic studies confirmed that product formation is possible only at very high temperature (140–150°C) and at lower temperature (90–100°C) formation of 14‐aryl‐14H‐dibenzo(a,j)xanthenes was observed. Among the nine Lewis acids screened, iodine, P₂O₅ and Yb(OTf)₃ are found to be most effective catalyst for this multicomponent reaction.     

Visible‐Light‐Driven Self‐Coupling of Methylarenes Catalyzed by Ni2P@Cd0.5Zn0.5S Nanoparticles

The Ni₂P@Cd_0.5Zn_0.5S nanoparticles photocatalyzed self‐coupling of p‐xylene was reported here, and the corresponding coupling product 1,2‐di‐p‐tolylethane was obtained. The reaction could be extended to toluene derivatives with electron‐donating and electron‐withdrawing substituents. Ni₂P@Cd_0.5Zn_0.5S nanoparticles had already been characterized by XRD, ICP‐AES, SEM, TEM, UV/Vis, FL, XPS. The Mott–Schottky curves of Ni₂P@Cd_0.5Zn_0.5S were made through electrochemical methods. An active carbon free‐radical was captured through ESR measurement under irradiation. The research demonstrated this photocatalytic system feasible for the self‐coupling reaction of toluene derivatives.     

Preparations of Saturated N‐P‐N Type Secondary Phosphine Oxides and their Applications in Cross‐Coupling Reactions

A series of cyclohexane‐1,2‐diamine ( 3a – 3d ) and benzene‐1,2‐diamine derivatives ( 3e – 3h ) were pre‐ pared. Followed by hydrolysis, the reaction of 3a – 3c with PCl₃ successfully led to the formation of cor‐ responding metastable saturated heteroatom‐substituted secondary phosphine oxides (HASPO 4a – 4c ), a tautomer of the saturated heteroatom‐substituted phosphinous acid (HAPA). Whereas ambient‐stable diamine‐coordinated palladium complexes were obtained, HAPA‐coordinated palladium complexes were not successfully synthesized. The molecular structures of HASPO 4c , Pd(OAc)₂(3a) , PdBr₂(3b) and Pd(OAc)₂(3c) and [Cu(NO₃)(3d)⁺][NO₃ ^? ] were determined by single‐crystal X‐ray diffraction method. Catalysis of in‐situ Suzuki‐Miyaura cross‐coupling reactions for aryl bromides and phenylboronic acid using diamine 3a as ancillary ligand showed that the optimized reaction condition at 60 °C is the combination of 2 mmol % 3a /3.0 mmol KOH/1.0 mL 1,4‐dioxane/1 mmol % Pd(OAc)₂. Moreover, moderate reactivity was observed when using aryl chlorides as substrates (supporting infor‐ mation). When diamine 3d was employed in Heck reaction, good tolerance of functional groups of aryl bromides were observed while using 4‐bromoanisole and styrene as substrates. The optimized condi‐ tion for Heck reaction at 100 °C is 3 mmol % 3d /3.0 mmol CsF/1.0 mL toluene/3 mmol % Pd(OAc)₂. In general, cyclohexane‐1,2‐diamine derivatives exhibited better catalytic properties than those of benzene‐1,2‐diamines.     

Kinetics of the reaction of O3 with selected benzenediols

The kinetics of the reaction of O₃ with the aromatic vicinal diols 1,2‐benzenediol, 3‐methyl‐1,2‐benzenediol, and 4‐methyl‐1,2‐benzenediol have been investigated using a relative rate technique. The rate coefficients were determined in a 1080‐L smog chamber at 298 K and 1 atm total pressure of synthetic air using propene and 1,3‐butadiene as reference compounds. The following O₃ reaction rate coefficients (in units of cm³ molecule^?1 s^?1) have been obtained: k(1,2‐benzenediol) = (9.60 ± 1.12) × 10^?18, k(3‐methyl‐1,2‐benzenediol) = (2.81 ± 0.23) × 10^?17, k(4‐methyl‐1,2‐benzenediol) = (2.63 ± 0.34) × 10^?17. Absolute measurements of the O₃ rate coefficient have also been carried out by measuring the decay of the dihydroxy compound in an excess of O₃. The results from these experiments are in good agreement with the relative determinations. Atmospheric implications are discussed. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 223–230, 2003     

Influence of the Metal Ions on the Allylic Rearrangement Reaction of 3,4,5,6‐Tetrahydrophthalic Anhydride

To further investigate the influence of metal ions on the allylic rearrangement of 3,4,5,6‐tetrahydrophthalic anhydride during the hydrothermal reaction, metal ions such as manganese(II), zinc(II) and cadmium(II) have been employed in the synthesis, which leads to the formation of three new lamellar coordination polymers, [Mn^II₅(µ₃‐OH)₃(1‐chec)(1,2‐chedc)(2,3‐chedc)₂(H₂O)] ( 3Mn) , [Zn^II₅(µ₃‐OH)₃(1‐chec)(1,2‐chedc)(2,3‐chedc)₂(H₂O)] ( 4Zn ), and [Cd^II₃(µ₃‐OH)₂(1,2‐chedc)₂] ( 5Cd) (1‐chec=cyclohexene‐1‐carboxylate, 1,2‐chedc=cyclohexene‐1,2‐dicarboxylate, 2,3‐chedc=cyclohexene‐1,2‐dicarboxylate). Interestingly, the allylic rearrangement reaction is metal‐dependent, which occurs only in 3Mn and 4Zn , resulting in the formation of one chiral carbon atom of the corresponding dicarboxylate ligands in both compounds. In addition, the magnetic property of compound 3Mn was studied, which revealed strong antiferromagnetic interactions between the metal centers.     

Why are reactions of 2‐ and 8‐thioquinoline derivatives with iodine different?

The crystal structures of 1,2‐dihydro‐1,1′‐bi[thiazolo[3,2‐a]quinoline]‐10a,10a′‐diium diiodide hemihydrate, C₂₂H₁₆N₂S₂²⁺·2I⁻·0.5H₂O, and 1,2‐dihydro‐1,1′‐bi[thiazolo[3,2‐a]quinoline]‐10a,10a′‐diium iodide triiodide, C₂₂H₁₆N₂S₂²⁺·I⁻·I₃⁻, obtained during the reaction of 1,4‐bis(quinolin‐2‐ylsulfanyl)but‐2‐yne (2TQB) with iodine, have been determined at 120 K. The crystalline products contain the dication as a result of the reaction proceeding along the iodocyclization pathway. This is fundamentally different from the previously observed reaction of 1,4‐bis(quinolin‐8‐ylsulfanyl)but‐2‐yne (8TQB) with iodine under similar conditions. A comparative analysis of the possible conformational states indicates differences in the relative stabilities and free rotation for the 2‐ and 8‐thioquinoline derivatives which lead to a disparity in the convergence of the potential reaction centres for 2TQB and 8TQB.     

Synthesis of 1,2,3,4‐Tetrahydro‐1,2‐dimethylidenenaphthalene: A Reactive s‐cis‐Butadiene Undergoing Highly Chemo‐ and Regioselective Cyclodimerization

1,2,3,4‐Tetrahydro‐1,2‐dimethylidenenaphthalene 11 has been derived in three steps from tetralone. In the condensed state and at −80°, it undergoes a highly chemo‐ and regioselective cyclodimerization to give 3,3′,4,4′‐tetrahydro‐2‐methylidenespiro[naphthalene‐1(2H),2′(1′H)‐phenanthrene] ( 14 ), the structure of which has been established by single‐crystal X‐ray‐diffraction analysis. Dimer 14 undergoes cycloreversion to diene 11 under flash‐pyrolysis conditions. The reaction of diene 11 with SO₂ occurs without acid promoter at −80° and gives a mixture of (±)‐1,4,5,6‐tetrahydronaphth[1,2‐d][1,2]oxathiin 2‐oxide ( 23 ; a single sultine), 1,3,4,5‐tetrahydronaphtho[1,2‐c]thiophene 2,2‐dioxide ( 25 ), and dimer 14 . The high reactivity of diene 1 in its Diels‐Alder cyclodimerization and its highly regioselective hetero‐Diels‐Alder addition with SO₂ can be interpreted in terms of the formation of relatively stable diradical intermediates or by concerted processes with transition states that can be represented as diradicaloids.     

Using the 1,2‐dihydro‐1,2‐diphosphinine ring as a template for the synthesis of new bicyclic structures and new trans‐chelating bis‐phosphines

The 1,2‐dihydro‐1,2‐diphosphinine decacarbonylditungsten complex 1 has been used as a synthetic equivalent of the corresponding 1,2‐dianion 2 . These two 1,2‐positions can be linked by a (CH₂)₄ bridge to yield a [4.4.0] bicyclic structure 6 whose identity has been confirmed by X‐ray crystal structure analysis. Alternatively, two ω‐iodohexyl chains can be grafted onto these positions and the resulting diiodo derivative 9 transformed into a long‐chain bis‐phosphine 10 by reaction with lithium diphenylphosphide. This bis‐phosphine gives a chelate complex with PdCl₂ whose trans‐stereochemistry was established by X‐ray crystal structure analysis. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:44–48, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20073     

Synthesis of poly(L‐lactide)‐grafted pullulan through coupling reaction between amino group end‐capped poly(L‐lactide) and carboxymethyl pullulan and its aggregation behavior in water

Poly(L ‐lactide) (PLLA) with terminal primary amino groups (PLLA‐NH₂) was synthesized and used to construct PLLA‐grafted pullulan (Pul‐g‐PLLA). It consisted of a hydrophilic carboxymethyl Pul (CM‐Pul) main chain and hydrophobic PLLA graft chains that were created through a direct coupling reaction between PLLA‐NH₂ and CM‐Pul using 2‐ethoxy‐1‐(ethoxycarbonyl)‐1,2‐dihydroquinoline as a condensation reagent. Pul‐g‐PLLAs with over 78 wt % sugar unit content were found to form nanometer‐sized aggregates in water. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5482–5487, 2004     

Iron(III) Chloride Catalyzed Oxidative Coupling Reaction of 1,2‐Diarylethylene Derivatives

A nontoxic FeCl₃ catalyzed intramolecular oxidative coupling reaction was developed for mild synthesis of a series of phenanthrenes with different substituents. The method involves cross dehydrogenative coupling of a variety of 1,2‐diarylethylene derivatives with di‐tert‐butylperoxide (DTBP) as a sole oxidant at room temperature in CH₂Cl₂/TFA (9:1 V/V) to yield phenanthrenes in good to excellent yields.     

Electrochemical Reduction of 1,2-Di（p-tolylimino）ethane and 1,2-Di（2,4-dimethylphenylimino）ethane in Dimethylformamide

1,2-Di（p-tolylimino）ethane （Ⅰ） and 1,2-Di（2,4-dimethylphenylimino）ethane （Ⅱ） were synthesized and their electrochemical behavior investigated in dimethylformamide using classical voltammetry, differential pulse voltammetry, cyclic voltammetry, chronoamperometry, controlled potential electrolysis and coulometry. Both bis-Schiff base ligands examined show a cathodic irreversible peak which corresponds to one-electron reduction of the substrate to form anion radical. According to the fact obtained from cyclic voltammetry, that the current function （ip/v^1/2） is a decreasing function of the scan rate, it can be concluded that there is a following coupling chemical reaction （EC mechanism）. Thus, the most probable mechanism of electroreduction of both ligands is the coupling of two radicals to form a dimer.     

Regio‐ and Stereoselective Reductive Coupling of Bicyclic Alkenes with Propiolates Catalyzed by Nickel Complexes: A Novel Route to Functionalized 1,2‐Dihydroarenes and γ‐Lactones

7‐Oxabenzonorbornadienes derivatives 1 a – d underwent reductive coupling with alkyl propiolates CH₃C?CCO₂CH₃ ( 2 a ), PhC?CCO₂Et ( 2 b ), CH₃(CH₂)₃C?CCO₂CH₃ ( 2 c ), CH₃(CH₂)₄C?CCO₂CH₃ ( 2 d ), TMSC?CCO₂Et ( 2 e ), (CH₃)₃C?CCO₂CH₃ ( 2 f ) and HC?CCO₂Et ( 2 g ) in the presence of [NiBr₂(dppe)] (dppe=Ph₂PCH₂CH₂PPh₂), H₂O and zinc powder in acetonitrile at room temperature to afford the corresponding 2alkenyl‐1,2‐dihydronapthalen‐1‐ol derivatives 3 a – n with remarkable regio‐ and diastereoselectivity in good to excellent yields. Similarly, the reaction of 7azabenzonorbornadienes derivative 1 e with propiolates 2 a, b and d proceeded smoothly to afford reductive coupling products 2alkenyl‐1,2‐dihydronapthalene carbamates 3 o – p in good yields with high regio‐ and stereoselectivity. This nickel‐catalyzed reductive coupling can be further extended to the reaction of 7oxabenzonorbornene derivatives. Thus, 5,6‐di(methoxymethyl)‐7‐oxabicyclo[2.2.1]hept‐2‐ene ( 4 ) reacted with 2 a and 2 d to furnish cyclohexenol derivatives bearing four cis substituents 5 a and b in 81 and 84 % yield, respectively. In contrast to the results of 4 with 2 , the reaction of dimethyl 7oxabicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboxylate ( 6 ) with propiolates 2 a – d afforded the corresponding reductive coupling/cyclization products, bicyclo[3.2.1]γ‐lactones 7 a – d in good yields. The reaction provides a convenient one‐pot synthesis of γ‐lactones with remarkably high regio‐ and stereoselectivity.     

Crystal structure and photoreactivity of a halogen‐bonded cocrystal based upon 1,2‐diiodoperchlorobenzene and 1,2‐bis(pyridin‐4‐yl)ethylene

The formation of a photoreactive cocrystal based upon 1,2‐diiodoperchlorobenzene ( 1,2‐C₆I₂Cl₄ ) and trans‐1,2‐bis(pyridin‐4‐yl)ethylene ( BPE ) has been achieved. The resulting cocrystal, 2( 1,2‐C₆I₂Cl₄ )·( BPE ) or C₆Cl₄I₂·0.5C₁₂H₁₀N₂, comprises planar sheets of the components held together by the combination of I…N halogen bonds and halogen–halogen contacts. Notably, the 1,2‐C₆I₂Cl₄ molecules π‐stack in a homogeneous and face‐to‐face orientation that results in an infinite column of the halogen‐bond donor. As a consequence of this stacking arrangement and I…N halogen bonds, molecules of BPE also stack in this type of pattern. In particular, neighbouring ethylene groups in BPE are found to be parallel and within the accepted distance for a photoreaction. Upon exposure to ultraviolet light, the cocrystal undergoes a solid‐state [2 + 2] cycloaddition reaction that produces rctt‐tetrakis(pyridin‐4‐yl)cyclobutane ( TPCB ) with an overall yield of 89%. A solvent‐free approach utilizing dry vortex grinding of the components also resulted in a photoreactive material with a similar yield.