An Empirical Correction Term to Density Functional Theory for the Description of the TiCl4-Lewis Base Complexes

Calorimetric and computational investigation on the interaction of TiCl₄ with some Lewis bases (esters and ethers) is presented. The bases were chosen for their relevance in heterogeneous Ziegler-Natta polymerization of propene. Comparison of the theoretical data with the calorimetric data indicates that calculations consistently underestimate the experimental binding energies. In light of this consistency, we propose that an empirical correction term added to the theoretical binding energies could represent an empirical solution for the prediction of the TiCl₄/donor binding energies with reasonable accuracy.     

conversion of trimethylsilyl ethers to acetyl or formyl esters with TiCl4

A simple method is described for the efficient conversion of trimethylsilyl ethers to their corresponding acetyl and formyl esters in refluxing ethyl acetate or ethyl formate in the presence of TiCl₄.     

A mild copper catalyzed method for the selective deprotection of aryl allyl ethers

Copper boryl reagents enable the selective cleavage of aryl allyl ethers to the corresponding phenols in good to moderate yields.     

Diarylmethyl ethers and Pd salts or complexes: a perfect combination for the protection and deprotection of alcohols

Primary and secondary alcohols are easily protected as diphenylmethyl (DPM) or bis(methoxyphenyl)methyl (BMPM) ethers in good yield using PdCl₂(CH₃CN)₂ as catalyst in dichloroethane at 60 or 20 °C, respectively. These conditions are compatible with other functional and protecting groups such as halides, esters, acetal, benzyl, para-methoxybenzyl, benzyloxycarbonyl, and tert-butyldiphenylsilyl. Good selectivity was observed in favor of primary over secondary alcohols. Deprotection of diphenylmethyl or bis(4-methoxyphenyl)methyl ethers was efficiently achieved at room temperature using PdCl₂(CH₃CN)₂ in dichloroethane in the presence of 10 equiv of ethanol.     

Investigating green ethers for the precipitation of peptides after global deprotection in solid-phase peptide synthesis

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A new method for the deprotection of benzyl ethers or the selective protection of alcohols

A new selective method for the deprotection of benzyl ethers situated next to alcohols in the alpha, beta, or gamma position is presented which uses either NIS or DIB/I2 as a reagent. After initial formation of a hypoiodite intermediate, the reaction is believed to follow a radical pathway to resemble the Hoffman-Loffler-Freytag reaction. The formation of the intermediate hypoiodite is suggested on the basis of NMR studies. Depending on the substrate, the corresponding benzylidene derivatives or diols are isolated.     

TiCl4-catalyzed indirect anti-Markovnikov hydration of alkynes: application to the synthesis of benzo[b]furans

An efficient methodology for the indirect anti-Markovnikov hydration of unsymmetrically substituted terminal and internal alkynes is based on TiCl4-catalyzed hydroamination reactions. Its application to ortho-alkynylhaloarenes, followed by a copper-catalyzed O-arylation, provides flexible access to substituted benzo[b]furans.     

1-Decanethiol, a new reagent for the odorless deprotection of aryl methyl ethers

1-Decanethiol has been found to be an excellent reagent for the deprotection of aryl methyl ethers. This newly developed protocol afforded the corresponding phenols in good to excellent yields. A clear advantage of 1-decanethiol over the more commonly used thiols is the easy extraction of both the deprotecting reagent and the reaction byproduct into the aqueous phase, which allows an essentially odorless work-up.     

A facile method for the rapid and selective deprotection of methoxymethyl (MOM) ethers

We describe a rapid and efficient method for selective deprotection of methoxymethyl (MOM) ethers using ZnBr₂ and n-PrSH, which completely removed MOM from diverse MOM ethers of primary, secondary, and tertiary alcohols or phenol derivatives. The deprotection takes less than ten minutes with both high yield and selectivity in the presence of other protecting groups. In addition, the rapid deprotection of MOM ethers of tertiary hydroxyls in high yield with no epimerization allows MOM to be a suitable protecting group for tertiary alcohols.     

Model kinetic study of TiCl4-induced ionization of polyisobutene capped with diphenylethylene application to the synthesis of block copolymers

The use of non-homopolymerizable monomers such as 1,1-diphenylethylene (DPE) in the synthesis of functional polymers and block copolymers by cationic polymerization has been recently reported. The most important parameters in this process, the kinetics and extent of ionization and capping as well as the stability of the cation, were investigated by studying the reaction with TiCl₄ of 1-methoxy-1,1-diphenyl-3,3,5,5-tetramethylhexane, a model for DPE-capped polyisobutene chain-end. This study was performed using ¹H NMR and the high-purity stopped-flow device coupled with UV-visible spectroscopy.     

An Efficient System TiCl4-Al for the Homocoupling Reaction of Aromatic Aldehydes

IntroductionThe deductive coupling of carbonyl compounds constitutes an important method for theformation of carbon--carbon bonds. In recent decades, a large number of coupling reagents areemployed['], such as metals Mg['J, Al[3], Zn[4], Te[5] and various low-valent complexes ofTi[6), ZrlvJ, V[sl, NbloJ, Snllo] or SmlllJ etc., can be used for the efficient syntheses of interor intramolecular pinacol coupling compounds with high yields. However, most of the conventional reductive-coupling…     

TiCl4-mediated reduction of 1,3-diketones with BH3-pyridine complex: a highly diastereoselective method for the synthesis of syn-1,3-Diols

[reaction: see text] 1,3-Diketones can be reduced in high yields and with excellent diastereoselectivity to the corresponding syn-1,3-diols by carrying out the reaction with BH3-pyridine complex in CH2Cl2 at -78 degrees C in the presence of an equivalent of TiCl4 and 0.1 equiv of pyridine. This protocol shows a general character: excellent results are obtained when the groups bound to the carbonylic functions are linear or branched carbon chains and aromatic or benzylic frameworks as well.     

Harnessing open-source technology for low-cost automation in synthesis: Flow chemical deprotection of silyl ethers using a homemade autosampling system

An inexpensive homemade 3-axis autosampler was used to facilitate the automation of an acid catalysed flow chemical desilylation reaction. Harnessing open-source software technologies (Python, OpenCV), an automated computer-vision controlled liquid-liquid extraction step was used to provide effective inline purification. A Raspberry Pi single-board computer was employed to interface with the motors used in the autosampler and actuated fluidic valves.     

An efficient strategy for the synthesis of endocyclic enol ethers and its application to the synthesis of spiroacetals

An efficient strategy for the synthesis of endocyclic enol ethers based on a Suzuki-Miyaura coupling/ring-closing metathesis sequence has been developed. The strategy has successfully been applied to the synthesis of spiroacetals, including cytotoxic marine metabolites attenols A and B.     

A facile and catalytic method for selective deprotection of tert-butyldimethylsilyl ethers with copper(II) bromide

Copper(II) bromide is found to be a simple and efficient catalyst for selective deprotection of tert-butyldimethylsilyl ethers of alcohols/phenols at ambient temperature. Various labile functional groups such as ketal, alkene, ketone, OTBDPS, OTHP and allyl and benzyl ethers are found to be compatible under the reaction conditions.     

Microwave-assisted synthesis of 1,3-dialkyl ethers of calix[4]arenes: application to the synthesis of cesium selective calix[4]crown-6 ionophores

Partial etherification of phenolic-OH groups of calix[4]arenes with various alkyl halides/tosylates and K₂CO₃ under microwave irradiation afforded 1,3-dialkoxycalix[4]arenes in their cone conformation only as predominant/sole product in good yields (71–85%). The protocol was found to be much superior to conventional heating both in terms of yield and reaction time. Some of the 1,3-dialkoxycalix[4]arenes were elaborated further to the syntheses of cesium selective calix[4]crown-6 ionophores.     

Platinum(II)-catalyzed reaction of 2-alkynylbenzoates or benzothioates with vinyl ethers: a concise method for synthesis of 1-acyl-4-alkoxy- or 1-acyl-4-alkylsulfanylnaphthalene derivatives

[reaction: see text] A concise method for the preparation of 1-acyl-4-alkoxy- or 1-acyl-4-alkylsulfanylnaphthalenes has been developed by the reaction of o-ethynylbenzoates or benzothioates with vinyl ethers, in the presence of a catalytic amount of PtCl(2). It is proposed that the reaction proceeds through [3 + 2]-cycloaddition of the platinum-containing carbonyl ylides followed by 1,2-alkyl migration.     

Gold-catalyzed synthesis of oxygen- and nitrogen-containing heterocycles from alkynyl ethers: application to the total synthesis of andrachcinidine

In this paper we report that homopropargylic ethers containing pendent oxygen or nitrogen nucleophiles react with electrophilic gold catalysts in the presence of water to form saturated heterocyclic ketones. Mechanistic studies demonstrated that the reactions proceed through a sequence of alkyne hydration, alkoxy group elimination, and intramolecular conjugate addition. Diastereoselectivities for tetrahydropyran and piperidine formation are very good to excellent. This method has been applied to an efficient total synthesis of the natural product andrachcinidine. Utilizing propargylic ether substrates rather than homopropargylic ethers promotes regioselective hydration of internal alkynes, thereby expanding the scope of products that can be accessed through this protocol.