Selective palladium-catalyzed arylation(s) of benzaldehyde derivatives by N-heterocarbene ligands

The 2- or 2,6-position(s) of aromatic aldehydes were directly and selectively arylated with aryl chlorides or bromides in the presence of a catalytic system prepared in situ from Pd(OAc)₂, imidazolinium chlorides (1-5) and Cs₂CO₃.     

Highly efficient synthesis of capsaicin analogues by condensation of vanillylamine and acyl chlorides in a biphase H2O/CHCl3 system

Highly efficient synthesis of capsaicin analogues was developed using condensation of vanillylamine with acyl chlorides in a biphase H₂O/CHCl₃ system under mild conditions. For C4-C18 aliphatic or aromatic acyl chlorides, the yields were up to 93-96% with high purity after a simple work-up procedure, and only 1-1.16 equiv of acyl chloride was needed in the reaction.     

硫酸亚铈催化的芳香化合物与苄基醇、烯丙醇类化合物以及苄基氯的傅-克烷基化反应研究

硫酸亚铈作为一种便宜的和有效的催化剂催化芳香化合物与苄基醇、烯丙醇类化合物和苄基氯的傅-克烷基化反应. 在1～10 mol%的硫酸亚铈存在下, 芳香化合物分别与苄基醇、烯丙醇类化合物和苄基氯能够顺利有效地进行傅-克烷基化反应. 此外, 催化剂能回收, 再次使用三次也没有明显地失去催化活性.     

Mild Cobalt‐Catalyzed Negishi Cross‐Couplings of (Hetero)arylzinc Reagents with (Hetero)aryl Halides

A catalytic system consisting of CoCl₂ ? 2 LiCl (5 mol %) and HCO₂Na (50 mol %) enables the cross‐coupling of various N‐heterocyclic chlorides and bromides as well as aromatic halogenated ketones with various electron‐rich and ‐poor arylzinc reagents. The reactions reached full conversion within a few hours at 25 °C.     

Oxidation of aromatic and aliphatic triisopropylsilanylsulfanyls to sulfonyl chlorides: preparation of sulfonamides

A series of aromatic and aliphatic triisopropylsilanylsulfanyls were prepared and oxidized to the sulfonyl chlorides with KNO₃/SO₂Cl₂. The sulfonyl chlorides were characterized via their conversion to sulfonamides.     

PdCl2(Ph3P)2/Salicylaldimine Catalyzed Diarylation of Anilines with Unactivated Aryl Chlorides

Triphenylphosphine and salicylaldimine could be used as a mixed ligand system to obtain a high catalytic activity for palladium catalyzed diarylation of primary anilines with unactivated aryl chlorides by the synergistic effect of ligands. The activity and selectivity of the catalytic system could be improved by modifying the structure of salicylaldimine. In refluxing o ‐xylene, PdCl₂(Ph₃P)₂ with 2,5‐ditrifluoromethyl N ‐phenylsalicylaldimine as a coligand shows high efficiency for the diarylation of various anilines. The catalytic system shows good toleration for the steric hindrance of the substrates. The facile catalytic system works as well on the multiple arylation of 1,1′‐biphenyl‐ 4,4′‐diamine with aryl chlorides to afford N ,N ,N′ ,N′ ‐tetraaryl‐1,1′‐biphenyl‐4,4′‐diamines which are important intermediates of organic light emitting diode (OLED) hole transport materials.     

Pd2dba3/P(i-BuNCH2CH2)3N: a highly efficient catalyst for the one-pot synthesis of trans-4-N,N-diarylaminostilbenes and N,N-diarylaminostyrenes

A Pd₂dba₃/P(i-BuNCH₂CH₂)₃N catalyzed one-pot synthesis of unsymmetrically substituted trans-4-N,N-diarylaminostilbenes and both symmetrically and unsymmetrically substituted N,N-diarylaminostyrene derivatives is reported. The procedure involves two or more palladium catalyzed sequential coupling reactions (an amination and an inter-molecular Heck reaction) in one-pot using the same catalyst system with two different aryl halides, including aryl chlorides and hetero aryl halides as the coupling partners.     

Deprotonative Metalation of Substituted Benzenes and Heteroaromatics Using Amino/Alkyl Mixed Lithium–Zinc Combinations

Different homoleptic and heteroleptic lithium–zinc combinations were prepared, and structural elements obtained on the basis of NMR spectroscopic experiments and DFT calculations. In light of their ability to metalate anisole, pathways were proposed to justify the synergy observed for some mixtures. The best basic mixtures were obtained either by combining ZnCl₂ ? TMEDA (TMEDA=N,N,N′,N′‐tetramethylethylenediamine) with [Li(tmp)] (tmp=2,2,6,6‐tetramethylpiperidino; 3 equiv) or by replacing one of the tmp in the precedent mixture with an alkyl group. The reactivity of the aromatic lithium zincates supposedly formed was next studied, and proved to be substrate‐, base‐, and electrophile‐dependent. The aromatic lithium zincates were finally involved in palladium‐catalyzed cross‐coupling reactions with aromatic chlorides and bromides.     

Aromatic H／D Exchange Reaction Catalyzed by Groups 5 and 6 Metal Chlorides

Groups 5 and 6 metal chlorides such as MoCl5, WCI6, NbCl5 and TaCl5 were found to be simple and very efficientcatalysts for the aromatic H/D exchange reactions. Compared with other metal chlorides such as ZnCl2, SnCl4 and TiCl4, groups 5 and 6 metal chlorides showed better catalytic activity in the H/D exchange reaction of naphthalene with C6D6. Deuteration of anthracene using MoC15 as a catalyst proceeded within 24 h at room temperature. Other aromatic compounds such as toluene, diphenylmethane and 1,1,2-triphenylethane were also deuterated smoothly in C6D6 within 24 h at room temperature.     

Synthesis of N-aryl-aza-crown ethers via Pd-catalyzed amination reactions of aryl chlorides with aza-crown ethers

The Pd₂(dba)₃/P(i-BuNCH₂CH₂)₃N (1) catalyst system effectively catalyzes the coupling of aza-crown ethers with electronically diverse aryl chlorides, affording N-aryl-aza-crown ethers in good yields. The Pd₂(dba)₃/P(i-BuNCH₂)₃CMe (2) catalyst system containing the more constrained bicyclic triaminophosphine is useful for aryl chlorides possessing base-sensitive ester, nitro, and nitrile functional groups.     

Acylation of aromatic alcohols and phenols over InCl3/montmorillonite K-10 catalysts

Montmorillonite K-10 clay supported InCl₃ is a highly active catalyst for the acylation of aromatic alcohols and phenols with different acyl chlorides. This catalyst can be reused in reactions a number of times without very significant loss of catalytic activity     

A general and efficient reduction of acyl chlorides to aldehydes by Sm(0)/Bu3P

A facile and efficient reduction of aromatic and aliphatic acyl chlorides to their corresponding aldehydes in the presence of Sm(0)/Bu₃P has been developed with broad scope. This method prevents over reduction of products, that is, the over-reduction of aldehydes to alcohols.     

An atom-efficient palladium-catalyzed cross-coupling reaction of triarylbismuths with acid chlorides: synthesis of diaryl and alkyl aryl ketones

The cross-coupling reaction of triarylbismuths with acid chlorides using a catalytic amount of PdCl₂/PPh₃ afforded the corresponding ketones in high yields. The reactions of aromatic and aliphatic acid chlorides occurred with atom efficiency, as 3 equiv of acid chlorides coupled effectively with 1 equiv of triarylbismuths to yield 3 equiv of the corresponding diaryl and alkyl aryl ketones.     

Palladium N‐heterocyclic‐carbene‐catalyzed ortho‐arylation of benzaldehyde derivatives

New, sterically demanding 1,3‐dialkylbenzimidazolium salts ( 2a–c ) as N‐heterocyclic‐carbene precursors have been synthesized and characterized. The ortho position of aromatic aldehydes was directly and selectively arylated with aryl chlorides in the presence of a catalytic system prepared in situ from Pd(OAc)₂, 1,3‐dialkylbenzimidazolium chlorides ( 2a–c ), and Cs₂CO₃. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:569–574, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20479     

Palladium-benzimidazolium salt catalyst systems for Suzuki coupling: development of a practical and highly active palladium catalyst system for coupling of aromatic halides with arylboronic acids

Palladium-benzimidazolium salt catalyst systems have been studied for the Suzuki coupling. A different substitutent effect has been uncovered with respect to nitrogen substituents in the benzimidazolium salts from the palladium-imidazolium salt analogs. A practical and highly active palladium catalyst system, PdCl₂/N,N′-dibenzylbenzimidazolium chloride 2, has been identified for the Suzuki coupling of aromatic halides with arylboronic acids. The coupling of a wide array of aromatic halides with arylboronic acids with the PdCl₂-2 catalyst system gave good to excellent yields. The effective palladium loading could be as low as 0.0001 mol% and 0.01-0.1 mol% for iodide and bromide substrates, respectively. The coupling of unactivated aromatic chlorides with arylboronic acids also gave good results using Cs₂CO₃ as base with a 2 mol% palladium loading. The electronic factors from aromatic halides exert a significant influence on the Suzuki coupling catalyzed by the PdCl₂-2 system while the electronic effect from the arylboronic counterparts is negligible. The aromatic halides with modest steric hindrance could also couple smoothly with phenylboronic acids using the PdCl₂-2 catalyst system.     

InBr3-Et3N promoted alkynylation of aldehydes and N,O-acetals under mild conditions: facile and simple preparation of propargylic alcohols and amines

The use of a novel InBr₃-Et₃N reagent system to promote addition reactions of 1-alkynes not only with a variety of aromatic or bulky aliphatic aldehydes but also with N,O-acetals is described. The corresponding propargylic alcohols or amines are produced in good to excellent yields.     

Acylation of Diethyl Phosphonoacetic Acid Via the MgCl2/Et3N System: A Practical Synthesis of β-Keto Phosphonates

A one pot simple procedure for the synthesis of β-keto phosphonates has been developed using the MgCl₂/Et₃N base system to generate the magnesium enolate of diethyl phosphonoacetic acid. This intermediate reacts with acid chlorides or imidazolides to give, after workup, the title compounds in good yields.     

Recent Progress Toward Trifluoromethylselenolation Reactions

Recently, a great deal of work has been done in the construction of C–CF₃ or C–SCF₃ bonds, because these fluorine groups display remarkable biological properties. Despite a trifluoromethylseleno group like CF₃ or SCF₃ may also have potential biological activity, the work on the construction of the C–SeCF₃ bond is rarely reported. This mini‐review highlights recent developments in trifluoromethylselenolation reactions using fluorine reagents, such as (Me₄N )SeCF₃ , ClSeCF₃ , [(bpy)Cu(SeCF₃ )]₂, Me₃SiCF₃ , and HCF₃ . Five approaches to the trifluoromethylselenolation of organic compounds are summarized: (1) trifluoromethylselenolation of aryl, alkyl, and heteroaryl halides, aromatic compounds, and boronic acids; (2) trifluoromethylselenolation of terminal alkynes and propargylic chlorides; (3) trifluoromethylselenolation of allylic bromides, vinyl halides, α‐bromo‐α,β‐unsaturated carbonyl compounds, and acyl chlorides; (4) trifluoromethylselenolation of diazo compounds; and (5) synthesis of trifluoromethyl selenides from selenocyanates and fluoroform.     

Fast and efficient synthesis of flavanones from cinnamic acids

A fast and efficient synthesis of flavanones from cinnamic acids in three steps has been developed. First, the cinnamic acid was converted to cinnamyol chlorides using SOCl₂. The acid chlorides were then treated with substituted phenols in BF₃?·?OEt₂ to furnish corresponding chalcones in 42(75% yields. Base-catalyzed cyclization of the chalcones at room temperature afforded corresponding flavones in 85–95% yields. The conversion of the cinnamic acid derivatives to corresponding chalcones was found to be sensitive to the position and nature of the substituents on the aromatic rings.     

Isoxazole‐Embedded Allylic Zinc Reagent for the Diastereoselective Preparation of Highly Functionalized Aldol‐Type Derivatives Bearing a Stereocontrolled Quaternary Center

Highly functionalized aldol‐type products bearing a β‐quaternary center and a stereoselectively controlled γ‐hydroxy function are readily prepared by the diastereoselective addition of an allylic zinc reagent embedded in an isoxazole ring to various aromatic and heteroaromatic aldehydes, in the presence of Lewis acids, such as MgCl₂ or LaCl₃?2 LiCl. After reductive cleavage of the N?O bond by using Fe, NH₄Cl, aldol‐type products bearing a stereocontrolled β‐quaternary center and a γ‐hydroxy group were observed. The benzylic reactivity of the isoxazolylmethylzinc reagent towards other electrophiles, such as acid chlorides, aryl and allylic halides, as well as aldehydes in the presence of BF₃?OEt₂ are also described.