Investigation into selective debenzylation and ring cleavage of quinazoline based heterocycles

The selective cleavage of different benzyl bonds within tetrahydroquinazoline and dihydroquinazolinone derived structures can be achieved by the usage of different reduction and debenzylation conditions thereby providing selective removal of O-benzyl protection groups as well as the cleavage of the ring structure within the quinazoline and quinazolinone systems.     

Selective debenzylation of benzyl esters by silica-supported sodium hydrogen sulphate

A new debenzylation of benzyl esters by silica-supported sodium hydrogen sulfate is described. The debenzylation could be achieved selectively and efficiently in good to excellent yields without affecting sensitive functional groups such as nitro, unsaturated bonds, and ethyl ester.     

Molecular structure and force field of boron tribromide as determined from combined analysis of gas electron diffraction and spectroscopic data and supported by quantum-chemical density-functional calculations

The thermal-average parameters of BBr₃ at 21(1) °C were obtained from a conventional analysis of gas electron diffraction (GED) data (r_g(B---Br) = 190.0(4) pm). The equilibrium structure and the force constants were refined from a joint analysis of the GED intensities and vibrational frequencies using different approximations. The simplest approximation (quadratic potential function in rectilinear coordinates) is suitable for the refinements of the equilibrium bond length (r^h_e(B---Br) = 189.6(4) pm) and the force constants of BBr₃. The molecule is planar within the error limits. Quantum-chemical density-functional calculations supported planarity of the molecule.     

Selective debenzylation of aromatic benzyl ethers by silica-supported sodium hydrogen sulfate

A new debenzylation of aromatic benzyl ethers by silica-supported sodium hydrogen sulfate is described. The process proceeds selectively and efficiently in good to excellent yields without affecting sensitive functional groups such as nitro, COOMe, aldehyde, ketone, and tosyl.     

Reaction of Triethyl Phosphite with Boron Tribromide

Summary.  Reaction of boron tribromide with triethyl phosphite led to the formation of triethyl tribromoborophosphate 1, a complex bearing a P→B bond. Received November 19, 1999. Accepted (revised) January 21, 2000     

Convenient phosphorus tribromide induced syntheses of substituted 1-arylmethylnaphthalenes from 1-tetralone derivatives

A series of 1-arylmethylnaphthalenes 7a-g and 11 have been synthesized conveniently in good yields at room temperature through phosphorus tribromide induced aromatization of 1-aryl-[3,4]-dihydronaphthyl-methanols 6a-g and 10, which were obtained from 1-tetralone derivatives.     

Kinetics and mechanism of oxidation of aliphatic alcohols by tetrabutylammonium tribromide

Oxidation of nine primary aliphatic alcohols by tetrabutylammonium tribromide (TBATB) in aqueous acetic acid leads to the formation of the corresponding aldehydes. The reaction is first order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to alcohols. The reaction failed to induce the polymerization of acrylonitrile. Tetrabutylammonium chloride has no effect on the reaction rate. The proposed reactive oxidizing species is the tribromide ion. The oxidation of [1,1-²H₂]ethanol exhibits a substantial kinetic isotope effect. The effect of solvent composition indicates that the rate increases with increase in the polarity of the solvent. The reaction is susceptible to both polar and steric effects of substituents. A mechanism involving transfer of a hydride ion in the rate-determining step has been proposed.     

Mild and efficient conversion of trifluoromethylarenes into tribromomethylarenes using boron tribromide

Tribromomethylarenes were prepared efficiently, at room temperature, from trifluoromethylarenes with boron tribromide as the brominating reagent. The present process is applicable to the preparation of various substituted benzotribromide derivatives from substituted benzotrifluoride compounds. p-Substituted benzotrifluoride compounds were found to be more reactive than o-substituted isomers under the given reaction conditions.     

Kinetics and mechanism of the oxidation of some vicinal and non-vicinal diols by tetrabutylammonium tribromide

Kinetics of oxidation of five vicinal and four non-vicinal diols, and two of their monoethers, by tetrabutylammonium tribromide (TBATB) has been studied. The vicinal diols yield products arising out of glycol-bond fission, while the non-vicinal diols produce the hydroxycarbonyl compounds. The reaction is first-order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to diols. The reaction fails to induce the polymerization of acrylonitrile. There is no effect of tetrabutylammonium chloride on the reaction rate. The proposed reactive oxidizing species is the tribromide ion. The effect of solvent composition indicates that the rate increases with increase in the polarity of the solvent. The oxidation of [1,1,2,2-²H₄] ethanediol shows the absence of any primary kinetic isotope effect. Values of solvent isotope effect, k(H₂O)/k(D₂O), at 288 K for the oxidation of ethanediol, propane-1,3-diol and 3-methoxybutan-1-ol are 3.41, 0.98 and 1.02 respectively. A mechanism involving a glycol-bond fission has been proposed for the oxidation of vicinal diols. Non-vicinal diols are oxidised by a hydride-transfer mechanism, as they are monohydric alcohols.     

Pyridinium tribromide catalyzed condensation of indoles and aldehydes to form bisindolylalkanes

An efficient synthetic method for bis(indol-3-yl)alkane derivatives has been developed.In the presence of 5 mol%of pyridinium tribromide(PTB),the condensation of indoles and aldehydes proceeded smoothly under mild conditions,giving rise to the corresponding bis(indol-3-yl)alkanes in good to excellent yields.     

Synthesis of cetyltrimethylammonium tribromide (CTMATB) and its application in the selective oxidation of sulfides to sulfoxides

The bright yellow crystalline cetyltrimethylammonium tribromide (CTMATB) reagent has been synthesized from the reaction of CTMAB and KBr with H₂MoO₄·H₂O, H₂O₂ and H₂SO₄ in the molar ratio 1:2:0.01:4:0.93. CTMATB selectively oxidizes a variety of dialkyl and alkyl aryl sulfides to the corresponding sulfoxides in high yields under mild conditions.     

A mild and efficient method for the methoxymethylation and acetylation of alcohols promoted by benzyltriphenylphosphonium tribromide

<正>A mild and efficient method for the conversion of alcohols to their corresponding methoxymethyl ethers and acetates using benzyltriphenylphosphonium tribromide(BTPTB) as catalyst is described.All reactions were performed under completely heterogeneous reaction conditions in good to high yields.     

A practical and efficient procedure for the cleavage of acylals to aldehydes catalyzed by indium tribromide in water

Indium tribromide (10 mol %) is an efficient catalyst for chemoselective cleavage of aryl acylals in refluxing water. A variety of acylals have been deprotected to give the corresponding parent aldehydes in high yield. The procedure presented is operationally simple, practical, and compatible with other sensitive functionalities such as methoxy, methyleneioxy, and benzyloxy groups present in the substrates.     

Synthesis and Application of Poly(diallyldimethylammonium tribromide)as a Novel Polymeric Brominating Agent

In this study, the synthesis and applications of a new supported tribromide reagent based on poly(diallyldimethylammonium chloride) is reported. This supported tribromide is used in α‐bromoacetalization of ketones, bromination of alkenes and regioselective bromination of activated aromatic compounds. This method is mild and no Br₂ and HBr were used. Other advantages of this reagent are stability, high efficiency, simple filtera‐ bility and reusability.     

Preparation of aromatic nitriles via direct oxidative conversion of benzyl alcohols,aldehydes and amines with pentylpyridinium tribromide in aqueous NH4OAc

Pentylpyridinium tribromide and aqueous ammonium acetate was used for the rapid oxidative conversion of benzyl alcohols, benzaldehydes and benzyl amines to the corresponding benzonitriles in good to excellent yields. This simple, mild and one-pot system provides easy workup and separation of the products.     

Benzylic Bromination of Toluene Derivatives with Boron Tribromide

A facile method for the benzylic bromination of toluene derivatives was developed. Various substituted toluenes were brominated with boron tribromide as bromine source in carbon tetrachloride at room temperature, affording their corresponding benzyl bromides in good yields.     

一种高效简易的聚(4-乙烯基三溴化吡啶)催化乙醇合成乙酸盐的方法(英文)

Poly(4-vinylpyridinium tribromide) is an efficient catalyst for the conversion of various alcohols to their corresponding acetate derivatives with acetic anhydride.This method has some advantages such as mild reaction conditions,good to excellent yields,and ease of work-up.     

Catechol reactivity: Synthesis of dopamine derivatives substituted at the 6-position

Dopamine is a ubiquitous neurotransmitter essential in the proper functioning of the human body. In addition to this critical role, the catecholamine core has shown utility as a scaffold for numerous drugs and in other applications, like metal detection and adhesive materials. Substituents at the 6-position of dopamine’s catechol core can modulate its stereoelectronic properties, the acidity of its phenolic hydroxyl groups, and the overall hydrophobicity of the molecule. Herein, we report the synthesis of a series of four novel dopamine analogues substituted at the 6-position of catechol core. The ¹H NMR chemical shift of the aromatic proton meta to the substituent correlated strongly with the Hammett σ_m constant, confirming the electronic properties of substituents.     

Aromatic Polyhedral Hydroxyborates: Bridging Boron Oxides and Boron Hydrides

No explosion , but per-B-hydroxylation occurs if the icosahedral boron hydrides [closo-B₁₂H₁₂]²⁻ (see picture), [closo-CB₁₁H₁₂]⁻, or closo-1,12-(CH₂OH)₂-1,12-C₂B₁₀H₁₀ are refluxed in 30 % hydrogen peroxide. Thus, the three isoelectronic species [closo-B₁₂(OH)₁₂]²⁻, [closo-1-H-1-CB₁₁(OH)₁₁]⁻, and closo-1,12-H₂-1,12-C₂B₁₀(OH)₁₀ were obtained. ○=BH, ○=BOH.     

Polyvinylpolypyrrolidonium tribromide as new and metal-free catalyst for the formylation and trimethylsilylation of hydroxyl group

Trimethylsilylation of alcohols was achieved using 1,1,1,3,3,3-hexamethyldisilazane(HMDS) as silylating agent,in the presence of polyvinylpolypyrrolidonium tribromide in acetonitrile at room temperature.Also a variety of alcohols were converted into alkyl formates by ethyl formate and a catalytic amount of polyvinylpolypyrrolidonium tribromide under solvent free conditions at room temperature.