Synthesis of allenes via gold-catalyzed intermolecular reaction of propargylic alcohols and aromatic compounds

Functionalized allenes are efficiently synthesized in moderate to high yield from gold-catalyzed intermolecular reaction of propargylic alcohols and aromatic compounds. The user-friendly process could be conducted under mild reaction conditions with easily accessible starting materials.     

Facile preparation of allenic hydroxyketones via rearrangement of propargylic alcohols

[formula: see text] Treatment of tertiary propargylic alcohols 13 with 3-diazo-2-butanone 6 and catalytic dirhodium tetraacetate in benzene gave good yields of the diastereomeric allenic hydroxyketones 14, with, in some cases, good diastereocontrol. These products are presumably formed via the [2,3]-sigmatropic rearrangement of an alpha-propargyloxy enol derivative. This reaction has been extended to the preparation of homoallylic hydroxyketones from allylic alcohols by reaction with 6 and the rhodium catalyst.     

A convenient palladium-catalyzed aerobic oxidation of alcohols at room temperature

A simple Pd-catalyzed aerobic oxidation of benzylic and aliphatic alcohols to the corresponding aldehydes and ketones at room temperature is described.     

Ruthenium-catalyzed synthesis of alkylidenecyclobutenes via head-to-head dimerization of propargylic alcohols and cyclobutadiene-ruthenium intermediates

The reaction of propargylic alcohols with carboxylic acid, or phenol derivatives, in the presence of the precatalyst [RuCl(cod)(C5Me5)] leads selectively to a variety of alkylidenecyclobutenes through head-to-head dimerization of propargylic alcohol. The first step is the formation of a cyclobutadiene-ruthenium intermediate resulting from the head-to-head coupling of two molecules of propargylic alcohol. On protonation with strong acids (HPF6, HBF4) dehydration of the cyclobutadiene complex leads to formation of an alkylidenecyclobutenyl-ruthenium complex. The X-ray structure of one such complex, [RuCl(C5Me5)(eta4-R'CCH--CH--C=CR2)] (R'=cyclohexen-1-yl, CR2 = cyclohexylidene) has been determined. Carboxylate is added at the less substituted carbon of the cyclic allylic ligand. DFT/B3 LYP calculations confirm that the intermediate arising from head-to-head coupling of alkyne to the RuClCp* species yields the cyclobutadiene-ruthenium complex more easily with propargylic alcohol than with acetylene.     

New efficient ruthenium catalysts for racemization of alcohols at room temperature

(η⁵-Pentaphenylcyclopentadienyl)RuCl(CO)₂ was found to catalyze efficiently the racemization of chiral alcohols such as (S)-1-phenylethanol, (S)-1-phenylpropan-2-ol, (S)-4-phenylbutan-2-ol and (S)-4-methoxy-1-phenylethanol at room temperature in the presence of a base. The catalytic activity of three other Ru(II) complexes was also investigated. The effects of halide and solvent were studied as well.     

Reactions of alcohols with α-alkoxyacroleins at room temperature

The first stage of the reactions of alcohols with α-alkoxyacroleins in an acidic medium at 20°C under kinetically controlled conditions is the Markovnikoff addition at the C=C bond to form 2,2-dialkoxypropanals (methylglyoxal ketals). Under conditions of thermodynamic control, subsequent acetalization of the aldehyde group occurs to form 1,1,2,2-tetraalkoxypropanes. When the duration of the reaction is further increased in the absence of a water acceptor, the ketal group undegroes hydrolysis and methylglyoxal acetals are formed. A method was developed for the preparation of methylglyoxal ketals. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2504–2507, December, 1998.     

A general and efficient FeCl3-catalyzed nucleophilic substitution of propargylic alcohols

A general and efficient FeCl3-catalyzed substitution reaction of propargylic alcohols with carbon- and heteroatom-centered nucleophiles such as allyl trimethylsilane, alcohols, aromatic compounds, thiols, and amides, leading to the construction of C-C, C-O, C-S and C-N bonds, has been developed.     

Mercuric acetate-mediated annulation of homopropargylic alcohols having thioether substituent. A general route for the synthesis of tetrasubstituted furans from propargylic dithioacetals

Treatment of an alkyl-substituted propargylic dithioacetal with ⁿBuLi followed by an aldehyde furnishes thio-substituted homopropargylic alcohol 7 which undergoes annulation in the presence of two equivalents of mercury acetate to give the corresponding mercurio-substituted furan 12. Reaction of 12 with iodine gives iodofuran in moderate to good yield.     

Highly enantioselective rhodium-catalyzed conjugate addition of arylboronic acids to enones at room temperature

The rhodium-phosphoramidite-catalyzed asymmetric conjugate addition of arylboronic acids to enones proceeds at room temperature using [Rh(OH)(cod)]₂ or [RhCl(cod)]₂/KOH as stable and readily available catalyst precursors.     

Syntheses of trifluoromethylated diene derivatives through the claisen rearrangement of trifluoromethylated propargylic and allylic alcohols

3-Trifluoromethyl-2Z, 4E-dienoate ($\text{14}$) and the dienamide ($\text{10}$,$\text{11}$) were prepared through the Claisen rearrangement of trifluoromethylated propargylic and allylic alcohols.     

A facile electrochemical synthesis of covellite nanomaterials at room temperature

A novel method for the electrochemical synthesis of covellite (CuS) nanoparticles (NPs) in aqueous phase was developed. In this experiment, thioglycerol (TG) is used as the catalyst for the hydrolysis of sodium thiosulfate, the sulfur source for the synthesis of CuS. Cu foil, which acts as the sacrificing anode, is oxidized to Cu²⁺ by applying a potential of 0.5 V while OH^- was produced on the cathode surface at the same time. The production of OH^- facilitates the reaction between Cu²⁺ and thiosulfate under the catalysis of TG. The evolution of hydrogen bubbles effectively prevents the deposition of copper sulfide on the cathode. Copper sulfide sols of “golden-brown”, and “dark-green” forms can be obtained by varying the concentration of TG. The “golden-brown” copper sulfide sols are also observed to convert to the green form with time, and the rate of this conversion process is faster at higher temperatures. X-ray diffraction (XRD) and chemical analysis indicate that the “dark-green” form of product is pure hexagonal phase CuS. The obtained CuS NPs were covered by a layer of TG as suggested by Fourier transform infrared (FTIR) data. The size and morphology of the particles are studied by transmission electron microscope (TEM).     

Air-stable racemization catalyst for dynamic kinetic resolution of secondary alcohols at room temperature

[reaction: see text] A novel racemization catalyst was synthesized for the dynamic kinetic resolution (DKR) of alcohols with a lipase at room temperature in the air. Furthermore, a polymer-supported derivative was also synthesized and tested as a recyclable catalyst for the aerobic DKR of alcohols.     

Oxidative esterification of primary alcohols at room temperature under aqueous medium

Oxidative esterification of aliphatic primary alcohols with bromide and bromate couple in aqueous acidic medium at room temperature is reported with a wide range of substrate scope for both aliphatic and cyclic alcohols and obtained excellent yields of products.     

Facile preparation of protected benzylic and heteroarylmethyl amines via room temperature Curtius rearrangement

A step-wise, room temperature procedure for acyl azide formation and the subsequent Curtius rearrangement of phenyl and heteroaryl acetic acids is described. We have developed a protocol for room temperature Curtius rearrangement in MeOH or CHCl₃ that provides an improvement over standard conditions, avoiding the use of additives or heat. This room temperature optimization of the Curtius rearrangement prevents the formation of side products often observed with benzylic acids, allowing access to a variety of benzylic and heteroarylmethyl amines.     

A general procedure for the synthesis of isoxazolidin-5-ones

Conjugate addition of N-substituted hydroxylamines to α,β-unsaturated esters followed by cyclisation of the adducts with lithium bis (trimethylsily)amide provides the first general means of synthesising isoxazolidin-5-ones, the N-benzyl derivatives of which may be hydrogenolised to β-aminoacids.     

Iodine-catalyzed allylation of 1,3-dicarbonyl compounds with allylic alcohols at room temperature

A highly efficient iodine-catalyzed allylation of 1,3-dicarbonyl compounds with a wide variety of allylic alcohols has been developed. The reaction is operationally straightforward and proceeds under very mild conditions at room temperature in good to excellent yields (up to 99%) and regioselectivity.     

A facile and rapid one-step synthesis of 8-substituted xanthine derivatives via tandem ring closure at room temperature

N-Bromo succinimide (NBS) was found to be an efficient and regioselective reagent in combination with AIBN for an unprecedented, facile and rapid one-step synthesis of 8-substituted xanthine derivatives at room temperature. The inexpensive, nontoxic and readily available NBS efficiently promoted the condensation of several aryl/cycloaryl/heteroaryl aldehydes with 5,6-diamino-1,3-dimethyluracils in presence of catalytic amount of AIBN in a single step via radical chain reaction. The notable advantages of this protocol were short reaction time, milder reaction conditions, simple work-up procedure, no requirement for chromatographic separation, use of non-hazardous reagent/solvent and applicable to a variety of substrates.     

A general efficient strategy for cis-3a-aryloctahydroindole alkaloids via stereocontrolled ZnBr(2)-catalyzed rearrangement of 2,3-aziridino alcohols

A short and general approach to the cis-3a-aryloctahydroindole alkaloids has been developed on the basis of a key stereocontrolled ZnBr(2)-catalyzed rearrangement of 2,3-aziridino alcohols. Two representative members, (+/-)-crinane and (+/-)-mesembrine, have been synthesized in 15% and 11% overall yields, respectively. [reaction: see text]