Reactions of acyl anions generated from acid chlorides and diiodosamarium

Acid chlorides react with SmI₂ to give α-diketones. Various experiments show that the initially formed acyl radical is rapidly transformed into an acyl anion which is thus generated by quite an unusual route.This species acylates acid chlorides, aldehydes and ketones in situ to give α-diketones and α-ketols. There are some limitations to this acyl anion chemistry but the reactions are realized with a good efficiency at room temperature in THF solution.     

Reactions of organometallic compounds catalyzed by transition-metal complexes: XI. The palladium-catalyzed reaction of acyl chlorides with Et6Sn2 as a route to symmetrical ketones and α-diketones

The reaction of aroyl chlorides (ArCOCl) with Et₆Sn₂ gives symmetrical ketones (Ar₂CO) or α-diketones ((ArCO)₂), depending on the nature of the palladium catalyst and the reaction conditions. The synthesis of α-diketones from AlkCOCl and HetCOCl has been performed for Alk = n-C₇H₁₅ and Het = 2-C₄H₃O (furyl). The palladium-catalyzed carbonylation of aryl iodides in the presence of Et₆Sn₂ may serve as another route to symmetrical α-diketones. Such a possibility has been demonstrated for the preparation of 4,4′-dimethoxybenzil from 4-iodoanisole, carbon monoxide, and Et₆Sn₂.     

A versatile access to unsymmetrical and symmetrical α-diketones via organotin reagents

Unsymmetrical α -diketones have been obtained via cross coupling of acyltins with acyl halides under PdCl₂(PPh₃)₂ catalysis while symmetrical α -diketones have been readily obtained via “in situ” formation of acyltins using hexabutylditin and acyl chlorides under similar experimental conditions.     

General and highly efficient fluorinated-N-heterocyclic carbene–based catalysts for the palladium-catalyzed Suzuki–Miyaura reaction

A general and highly efficient trifluoromethylated-N-heterocyclic carbene (NHC)-based catalyst for the palladium-catalyzed Suzuki–Miyaura reaction was reported. In the presence of the catalyst, reactions of non-activated aryl chlorides and triflates with aryl boronic acids occurred at room temperature with good to excellent yields (63–98%). In addition, catalysts generated from a combination of Pd(OAc)₂/imidazolium salt 6a is not only effective for the coupling of heteroaryl boronic acid with aryl halides and heteroaryl halides, but also efficient for coupling of other heteroaryl halides and heteroaryl boronic acids. Finally, the catalyst is highly effective for Suzuki–Miyaura reaction of aryl bromides and chlorides with 0.01–0.1 mol % loading if the temperature was raised at refluxed THF/H₂O.     

Stereospecific synthesis of a family of novel (E)‐2‐aryl‐1‐silylalka‐1,4‐dienes or (E)‐4‐aryl‐5‐silylpenta‐1,2,4‐trienes via a cross‐coupling of (Z)‐silyl(stannyl)ethenes with allyl halides or propargyl bromide

Stereospecific synthesis of a family of novel (E)‐2‐aryl‐1‐silylalka‐1,4‐dienes or (E)‐4‐aryl‐5‐silylpenta‐1,2,4‐trienes via a cross‐coupling of (Z)‐silyl(stannyl)ethenes with allyl halides or propargyl bromide is described. In the reaction with allyl bromide, either a Pd(dba)₂? CuI combination (dba, dibenzylideneacetone) in DMF or copper(I) iodide in DMSO–THF readily catalyzes or mediates the coupling reaction of (Z)‐silyl(stannyl)ethenes at room temperature, producing novel vinylsilanes bearing an allyl group β to silicon with cis ‐disposition in good yields. Allyl chlorides as halides can be used in the CuI‐mediated reaction. CuI alone much more effectively mediates the cross‐coupling reaction with propargyl bromide in DMSO–THF at room temperature compared with a Pd(dba)₂? CuI combination catalysis in DMF, providing novel stereodefined vinylsilanes bearing an allenyl group β to silicon with cis ‐disposition in good yields. Copyright © 2008 John Wiley & Sons, Ltd.     

Coupling of benzyl halides mediated through alkali metal supramolecular complexes. A novel route to poly(p-xylylene)

Coupling of benzyl bromide giving 1,2-diphenylethane was demonstrated to proceed at room temperature in THF solution mediated by the potassium/18-crown-6 supramolecular complex. Based on this model reaction a novel method for the low temperature synthesis of poly(p-xylylene) from α,α′-dibromo-p-xylene is proposed. Experimental evidence of the polymer structure was provided by solid-state ¹³C NMR and IR spectroscopy.     

The action of tris(triphenylphosphine)chlororhodium on polyhydromonosilanes

Dibromomethyllithium and its homologues RCBr₂Li (R = Bu, Me₃Si, Br) are prepared by metallation of the corresponding α,α-dibromo compounds with lithium diisopropylamide in THF at low temperature. Various coupling reactions are described (alkylation, hydroxyalkylation). New one-step preparations of α-bromoepoxides and α-bromoketones are reported.     

One‐Pot Synthesis of 2‐Substituted 4‐Aryl‐4,5‐dihydro‐3,1‐benzoxazepines from 2‐(2‐Aminophenyl)‐1‐arylethanols via Dehydration of the Corresponding Amides

An efficient method for the preparation of 2‐substituted 4‐aryl‐4,5‐dihydro‐3,1‐benzoxazepine derivatives under mild conditions has been developed. The reaction of 2‐(2‐aminophenyl)ethanols 1 with acid chlorides in the presence of excess Et₃N in THF at room temperature gave the corresponding N‐acylated intermediates 2 , which were dehydrated by treatment with POCl₃ to give 2‐substituted 4‐aryl‐4,5‐dihydro‐3,1‐benzoxazepines 3 in a one‐pot reaction.     

A facile stereoselective synthesis of (Z)-α-arylsulfonyl-α,β-unsaturated ketones

Palladium-catalyzed hydrostannylation of acetylenic sulfones 1 in benzene at room temperature gives highly regio- and stereoselectively (E)-α-stannylvinyl sulfones 2 in high yields. (E)-α-Stannylvinyl sulfones 2 are new difunctional group reagents which undergo Stille coupling reactions with acyl chlorides 3 to afford stereoselectively (Z)-α-arylsulfonyl-α,β-unsaturated ketones 4 in good yields. A one-pot stereoselective synthesis of (Z)-α-arylsulfonyl-α,β-unsaturated ketones 4 has also been achieved by tandem hydrostannylation-Stille coupling reaction of acetylenic sulfones 1 under mild conditions.     

A mechanistic study of the chromium(II)-mediated transformations of trichloromethyl alkyls and carbinols: evidence for carbene, carbyne, and carbenoid intermediates

Using CrCl₂ in THF at room temperature, trichloromethyl carbinols and trichloromethylalkanes are readily transformed to the highly reactive α-chlorocarbenes, carbynes and α-chloro-α-chromium(III) vinylidene carbenoids. A mechanistic study is carried out to determine the nature of the intermediates.     

THE BAYLIS—HILLMAN REACTION: TiCl4 MEDIATED COUPLING OF ALKYL VINYL KETONES WITH α-KETO ESTERS AND ALDEHYDES

TiCl₄ mediated coupling of alkyl vinyl ketones with α-keto esters and aldehydes provides respectively 2-aryl-2-hydroxy-3-methylene-4-oxoalkanoates and (Z)-keto allyl chlorides in 1 h time at room temperature. Similar coupling of trifluoromethyl phenyl ketone with methyl vinyl ketone produces 1,1,1-trifluoro-2-hydroxy-2-phenyl-3-methylenepentan-4-one.     

Facile generation of α,α-dibromodimethyl ketals from alkynes using TsNBr2

TsNBr₂ reacts with alkyne in the presence of methanol to form α,α-dibromodimethyl ketals instantaneously. The reaction proceeds smoothly at room temperature without using any other catalyst. The one step reaction can be carried out with both aromatic and aliphatic alkynes in excellent yield.     

Polymerization of methyl methacrylate using a metallocene catalyst system

Methyl methacrylate was polymerized with Cp₂YCl(THF) or IVB group metallocene compounds (i.e., Cp₂ZrCl₂ and Cp₂HfCl₂, etc.), in the presence of a Lewis acid like Zn(C₂H₅)₂. The Lewis acid was complexed with methyl methacrylate, which avoided the metallocene compounds being poisoned with a functional group. A living polymerization was promoted through the use of metallocene/MAO/Zn(C₂H₅)₂, which gave tactic poly(methyl methacrylate) with a high molecular weight. The polymer yield increases with polymerization time, which indicates that the propagation rate is zero in order in the concentration of the monomer. The polymer yield increases also with the concentration of Cp₂YCl(THF), which indicates the yttrocene to be the real catalyst. When the polymerization temperature exceeds room temperature, the poly(methyl methacrylate) cannot be synthesized by the Cp₂YCl(THF) catalyst. When the reaction temperature reachs −60 °C, the poly(methyl methacrylate) is high syndiotatic and molecular weight by the Cp₂YCl(THF)/MAO catalyst system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1184–1194, 2000     

Acylation of α-(N-carbamoyl)alkylcuprates and alkyl- or aryl(halo)cuprates

α-(N-Carbamoyl)alkylcuprates [R₂CuLi·LiX or RCuXLi (X=CN, Cl)] when prepared from THF soluble CuX·2LiCl (X=Cl, CN) undergo a reliable and generally high yield reaction with aroyl, alkanoyl, and alkenoyl chlorides to provide a rapid and efficient synthesis of α-carbamoyl ketones. Cuprates prepared from acyclic, cyclic, and a functionalized carbamate can be utilized. Although yields are a function of cuprate reagent and substrate structure, nearly quantitative yields can be obtained with reagents generated from 2RLi+CuCN·2LiCl. The use of reagents generated from CuCl·2LiCl are more efficient in the α-(N-carbamoyl)alkyl ligand, although yields are slightly lower. Acylation of alkyl(chloro)cuprates generated from one equivalent of CuCl·2LiCl and organolithium or Grignard reagents provides an efficient and high yield procedure for ketone synthesis.     

Palladium catalyzed Suzuki-Miyaura coupling with aryl chlorides using a bulky phenanthryl N-heterocyclic carbene ligand

A novel bis-phenanthryl N-heterocyclic carbene (NHC) based palladium acetate catalyst was effective for the coupling of various aryl and vinyl chlorides with organoboron compounds. N,N-Bis-(2,9-dicyclohexyl-10-phenanthryl)-4,5-dihydroimidazolium chloride 8 (H₂ICP·HCl) with Pd(OAc)₂ and KF·18-c-6 in THF at room temperature gave Suzuki-Miyaura coupling of aryl and vinyl chorides, including unactivated and di-ortho substituted substrates in high yields. Hindered tri- and tetra-ortho substituted products were also efficiently produced. Benzyl chloride was also found to be a useful coupling partner and trimethylboroxine was used to give methylated products. The effect of ligand, base, temperature, solvent, and reaction time are reported along with various substrates including halides and triflates.     

Selective 1,2-dihalogenation and oxy-1,1-dihalogenation of alkynes by N-halosuccinimides

1,2-Dihalogenation and oxy-1,1-dihalogenation of alkynes by N-halosuccinimides can be selectively realized through using different reaction conditions. α,β-Dihalo alkenes were obtained exclusively using THF as solvent without using any catalyst, while α,α-dihalo ketones were synthesized using a mixed solvent of THF and H₂O in the presence of FeCl₃·6H₂O. Terminal aromatic alkynes are smoothly transformed into α,α-dihalo ketones on water without a catalyst.     

Simultaneous Ring-Opened THF and insertion of diazoketone derived carbene into carbonyl O-H: Synthesis for β-keto enol ethers

A novel tandem synthesis of β-keto enol ethers was developed via the reaction of α-diazoketones, 1,3-diketones and THF catalyzed by cheap and available CuI under extremely simple conditions. During the course of the reaction, the ring-opened THF and diazocarbonyl derived carbene simultaneously inserted into O-H of 1,3-diketones.     

Reactivity of mixed organozinc and mixed organocopper reagents: 11. Nickel‐catalyzed atom‐economic aryl–allyl coupling of mixed (n‐alkyl)(aryl)zincs

Group selectivity in the allylation of mixed (n‐butyl)(phenyl)zinc reagent can be controlled by changing reaction parameters. CuCN‐catalyzed allylation in tetrahydrofuran (THF)–hexamethylphosphoric triamide is n‐butyl selective and also γ‐selective in the presence of MgCl₂, whereas CuI‐catalyzed allylation in THF in the presence of n‐Bu₃P takes place with a n‐butyl transfer:phenyl transfer ratio of 23:77 and an α:γ transfer ratio of phenyl of 76:24. NiCl₂(Ph₃P)₂‐catalyzed allylation in the presence of LiCl is phenyl selective with an α:γ ratio of 65:35. The reaction of methyl‐ or n‐butyl(aryl)zinc reagents with an allylic electrophile in THF at room temperature in the presence of NiCl₂(Ph₃P)₂ catalyst and LiCl as an additive provides an atom‐economic alternative to aryl–allyl coupling using diarylzincs. Copyright © 2014 John Wiley & Sons, Ltd.     

Anti-selective and regioselective aldol addition of ketones with aldehydes using MgI2 as promoter

The first example of a direct aldehyde-ketone coupling using the secondary amine piperidine as base in the presence of MgI₂ to generate high selectivity of anti-aldol products from unmodified ethyl ketones in high yield is reported. The coupling reactions were carried out in a one-pot reaction by mixing four reaction components at room temperature. In the case of unsymmetrical ketones, addition was made to the less hindered α-side.     

A novel one-pot synthesis of α-keto-1,3,4-oxadiazole derivatives based on isocyanide-Nef reaction

Various α-keto-1,3,4-oxadiazole derivatives were synthesized through a sequential intermolecular dehydrochlorination/intramolecular aza-Wittig reaction of carboxylic acids and imidoyl chloride intermediates, which were generated by isocyanide-Nef reaction of acyl chlorides and (N-isocyanimine) triphenylphosphorane (1) in CH₂Cl₂ at room temperature.