Lead-promoted Barbier-type reaction of aldehydes with propargyl bromides in aqueous media

This paper reports that the reaction of the propargyl bromides with aldehydes promoted by powdered lead in aqueous media.The selectivity and possible mechanism of these reactions are discussed.The yields of products for reaction of propargyl bromide are 31~71%.The ratios of al-lenyl alcohol and homopropargyl alcohol are 1:1.5 to 1:3.The product for reaction of phenyl propargyl bromide is allenyl alcohol and the yields are 52~84%.     

Regioselective Propargylation of Aldehydes with Propargyl Bromide Mediated by Sn-In in Aqueous Media under Microwave Irradiation

Tin-indium were employed in the propargylations of various aldehydes with propargyl bromide in the presence of SnCl2 and C6H5（CH3）3NBr under microwave irradiation to afford the corresponding homopropargyl alcohols exclusively in high yields. All the reactions were completed smoothly in predominantly aqueous media in 200 seconds only.     

2-Amino homopropargyl alcohols from the highly regioselective Ag2CO3-catalyzed nucleophilic openings of alkynyl epoxides by amines

The nucleophilic ring opening of propargyl epoxides by amines based on a silver catalyst is presented. The reaction takes place under mild conditions and features a high regioselectivity to provide an effective method for the synthesis of 2-amino homopropargyl alcohols in moderate to high yields.     

Studies on organophosphorus compounds 104. Reaction of carbanions derived from alkylphosphonates

Structural effect of substituents directly bonded to carbanions bearing a phosphorate moiety is examined. Nucleophihc addition of phosphonate carbanion to 1-nitroalkene followed by subsequent reaction with chlorotrimethylsilane leads to a series of 2-isoxazoline based on the formation of an alkene and silyl nitronate as a 1,3-dipole. On the other hand, addition of carbanion derived from isocyanomethylphosphonate to nitroalkene with the formation of nitronate followed by intromolecular cyclization provides substituted phosphoryl pyrroles.     

A CONVENIENT APPROACH OF DIYNE ALCOHOL AND TRIYNE ALCOHOL BY COPPER (I) AND PHASE TRANSFER CONDITION CATALYZED PROPARGYLATION OF PROPARGYL ALCOHOL

The copper(Ⅰ) catalyzed coupling reaction of substituted propargyl tosylate with propargyl alcohol proceeds smoothly at room temperature to give 2,5-diynyl alcohol under solid-liquid phase transfer condition. A number of 2,5-diynyl alcohols and 2,5,8-triynyl alcohols were synthesized in this way in good yield.     

BrФnsted Acidic Ionic Liquids: Novel Efficient,Cost-effective and Reusable Solvent-catalysts for Ritter Reaction

Several Brnsted acidic ionic liquids(ILs) were synthesized and used as dual solvent-catalysts for the Ritter reaction of benzonitrile with tert-butanol. In particular, IL11([NSPTEA][OTF]) showed excellent catalytic activity for the Ritter reaction. In the presence of IL11, various nitriles and tertiary alcohols as well as secondary alcohols were converted smoothly to the corresponding amides in good to excellent yields. In addition, this cost-effective ionic liquid [NSPTEA][OTF] was easily separated from the reaction mixture by extraction with a small amount of water, and was recycled five times without any significant loss in activity.     

Triphenylphosphine-Catalyzed Michael Addition of Alcohols to Acrylic Compounds

A facile triphenylphosphine-catalyzed Michael addition of alcohols to acrylic compounds was described. The reaction was carried out in open air at refluxing temperature in the presence of 10 mol% PPh3. Michael addition of saturated and unsaturated alcohols to acrylonitrile or acrylates has been examined. The reaction gave β-alkoxy derivatives with isolated yields of 5%-79%. PPh3 is cheaper and more stable than those trialkylphosphines previously used for the similar reactions, and the products can be easily separated from the reaction mixture via distillation.     

Oxidation of alcohols to aldehydes and ketones using selenium ionic liquid

A new type of ionic liquid supported selenium reagents were synthesized and found to be an excellent catalyst in the oxidation of alcohols to aldehydes and ketones in the presence of 30%H₂O₂.The predictable solubility of ionic liquids allows an easy separation of the oxidation products from the reaction mixture.Furthermore,the oxidation reaction can be carried out using an ionic liquid as the solvent,and the ionic liquid-supported selenium reagents can be recycled and used for four times with a little decrease in catalytic performance.     

Higher alcohol synthesis over Cu-Fe composite oxides with high selectivity to C2+OH

Cu-Fe composite oxides were prepared by co-precipitation method and tested for higher alcohol synthesis from syngas. The selectivity to C2+OH and C6+OH in alcohol distribution was very high while the methane product fraction in hydrocarbon distribution was rather low, demonstrating a promising potential in higher alcohols synthesis from syngas. The distribution of alcohols and hydrocarbons approximately obeyed Anderson-Schulz-Flory distribution with similar chain growth probability, indicating alcohols and hydrocarbons derived from the same intermediates. The effects of Cu/Fe molar ratio, reaction temperature and gas hourly space velocity (GHSV) on catalytic performance were studied in detail. The sample with a Cu/Fe molar ratio of 10/1 exhibited the best catalytic performance. Higher reaction temperature accelerated water-gas-shift reaction and led to lower total alcohols selectivity. GHSV showed great effect on catalytic performance and higher GHSV increased the total alcohol selectivity, indicating there existed visible dehydration reaction of alcohol into hydrocarbon.     

Palladium-catalyzed asymmetric carbamoyl-carbonylation of alkenes

An unprecedented palladium-catalyzed asymmetric carbamoyl-carbonylation of tethered alkenes with CO and alcohols has been developed. This reaction provided an efficient route to access oxindoles and γ-lactams bearing β-carbonyl substituted quaternary carbons in good yields with excellent chemo-, regio-and enantioselectivity. Gram-scale synthetic capability and facile transformations of the products to chiral spirooxindole and other functional molecules further illustrated the practicability of this reaction.     

One-pot, solvent-free regioselective addition reactions of propargyl bromide to carbonyl compounds mediated by Zn-Cu couple

A Barbier-type propargylation of carbonyl compounds with propargyl bromide has been achieved with reactive zinc-copper couple under solvent-free conditions. The reaction of aldehydes with propargyl bromide produced the unique homopropargyl alcohols in excellent yields at room temperature without the formation of homoallenyl alcohols. The ketones reacted with propargyl bromide to give the corresponding homopropargyl alcohols in good to excellent yields at −14 to −16 °C. The advantages of this method are excellent yields, short reaction time, high regioselectivity, and avoidance of the use of organic solvents.     

Reaction of Propargyl Bromide with Aldehydes in the Presence of Metallic Tin. Synthesis of Homopropargylalcohols and Homoallenylalcohols

In the presence of water, metallic tin and propargyl bromide reacted smoothly with aldehydes to give the corresponding homopropargyl alcohols (a) and homoallenyl alcohols (b). High Chemospecifity to bifounctional carbonyl compounds containing -OH, -X and -NO₂ etc. was obtained.     

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.     

A simple and facile synthesis of novel 1,2,3-triazole substituted pyrimidine derivatives

A series of novel indole and pyrimidine scaffolds bearing 1,2,3-triazoles have been designed and synthesized using click chemistry reaction conditions. Target compounds 9a-j were synthesized in the multi-step process. In the first step 5-substituted-1-methyl-1H-indole-3-carbaldehyde 2a-b reacted with ethyl cyanoacetate 3 and guanidine hydrochloride 4 in presence of L-Proline in ethanol undergoes cyclisation to form 5a-b . Further, 5a-b condensed with various benzaldehydes to form Schiff's base 6a-f , which further proporgylated with propargyl bromide to form 7a-f . Finally, 7a-f was subjected to click-chemistry with various azides in the presence of CuSO₄.5H₂O + sodium ascorbate mixture in Dimethylformamide at room temperature to obtain 2 + 3 cycloaddition products 9a-j in high yield. All these synthetic methods are mostly green and inexpensive with excellent yields.     

Divergent Reactivity of Homologue ortho‐Allenylbenzaldehydes Controlled by the Tether Length: Chromone versus Chromene Formation

The divergent behavior of two homologue allenals, namely, 2‐(buta‐2,3‐dienyloxy)‐ and 2‐(propa‐1,2‐dienyloxy)benzaldehydes, as cyclization substrates is described. 2‐(Buta‐2,3‐dienyloxy)benzaldehydes suffers a formal allenic carbocyclization reaction to afford chromenes, whereas 2‐(propa‐1,2‐dienyloxy)benzaldehydes react to yield chromones. The formation of chromenes is strictly a formal hydroarylation process divided into two parts, namely, allenic Claisen‐type rearrangement and oxycyclization. An unknown N‐heterocyclic carbene (NHC)‐catalyzed allenic hydroacylation reaction must be invoked to account for the preparation of chromones. ortho‐Allenylbenzaldehydes bearing either electron‐donating substituents or electron‐withdrawing substituents worked well to afford both the hydroarylation and hydroacylation products. This unexpected difference in reactivity can be rationalized by means of density functional theory calculations.     

Carbon-Carbon Bond Formation Reaction Promoted by Cadmium In Aqueous Media

Promoted by metallic cadmium allylilic and propargyl bromides react smoothly with aldehydes in aqueous DMF to give homoallylic and homopropargyl alcohols in moderate to good yields. It can also promote pinacol coupling of aromatic aldehydes. The metallic cadmium is produced in situ by the reduction of CdCl₂ H₂O with samarium metal.     

Kinetics and mechanism of the oxidation of substituted benzaldehydes by hexamethylenetetramine‐bromine

The oxidation of thirty‐six monosubstituted benzaldehydes by hexa‐methylenetetramine‐bromine (HABR), in aqueous acetic acid solution, leads to the formation of the corresponding benzoic acids. The reaction is first order with respect to HABR. Michaelis‐Menten–type kinetics were observed with respect to aldehyde. The reaction failed to induce the polymerization of acrylonitrile. There is no effect of hexamethylenetetramine on the reaction rate. The oxidation of [²H]benzaldehyde (PhCDO) indicated the presence of a substantial kinetic isotope effect. The effect of solvent composition indicated that the reaction rate increases with an increase in the polarity of the solvent. The rates of oxidation of meta‐ and para‐substituted benzaldehydes showed excellent correlations in terms of Charton's triparametric LDR equation, whereas the oxidation of ortho‐substituted benzaldehydes correlated well with tetraparametric LDRS equation. The oxidation of para‐substituted benzaldehydes is more susceptible to the delocalization effect but the oxidation of ortho‐ and meta‐substituted compounds displayed a greater dependence on the field effect. The positive value of γ suggests the presence of an electron‐deficient reaction center in the rate‐determining step. The reaction is subjected to steric acceleration when ortho‐substituents are present. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 615–622, 2000     

Chiral Aryl Pyridyl Alcohols as Enantioselective Catalysts in the Addition of Diethylzinc to Substituted Benzaldehydes

Chiral (5‐aryl‐10, 10‐dimethyl‐6‐aza‐tricyclo[7.1.1.0^2,7]undeca‐2(7),3,5‐trien‐8‐yl)‐diphenyl‐methanols were prepared from highly enantiopure (1R)‐(+)‐α‐pinene (> 97% ee), and applied in the enantioselective addition of diethylzinc to substituted benzaldehydes, to yield alcohols with the (S)‐configuration with an enantiomeric excess that typically ranges from 19 to 86%. Importantly, the electron‐withdrawing substituents at the meta‐position of the substituted benzaldehydes exhibited high enantioselectivity during alkylation using diethylzinc.     

Platinum‐Catalyzed Multi‐Step Reaction of Propargyl Alcohols with N‐Heteroaromatics

N‐Methyl indole reacts with but‐2‐yn‐1‐ol in the presence of PtCl₂ in MeOH giving indole derivatives having a substituted 3‐oxobutyl group at the 3‐position in good yield. Under the reaction conditions, various substituted indoles and substituted propargyl alcohols are successfully involved in the reaction giving the corresponding addition products in good to moderate yields. The catalytic reaction can be further extended to N‐phenyl pyrrole. In the present multi‐step reaction, PtCl₂ likely plays dual roles: as the catalyst for the rearrangement of propargyl alcohols to the corresponding alkenyl ketones and as the catalyst for the addition of indoles to the alkenyl ketones. Experimental evidence is provided to support the proposed mechanism.     

A Crystalline Diazadiborinine Radical Cation and Its Boron‐Centered Radical Reactivity

One‐electron oxidation of 1,4,2,5‐diazadiborinine 1 has been studied. While the reaction of 1 a bearing phenyl groups on the B atoms with AgAl{OC(CF₃)₃}₄ afforded a complex mixture, the same oxidation reaction with 1 b featuring bulky mesityl substituents on the B atoms rendered the corresponding cation radical 2 b as an isolable species. X‐ray diffraction analysis, EPR spectroscopy, and DFT calculations of 2 b revealed the delocalization of the unpaired electron over the entire π‐system of 2 b , as well as a large spin density (0.76 in total) on the two equivalent boron atoms. The chemical trapping reaction of 2 b with p‐benzoquinone and triphenyltin hydride afforded the dicationic species 3 containing two newly formed B?O bonds and the monocationic product 2b‐H containing a B?H bond, respectively, thus confirming the boron‐centered radical reactivity of 2 b .