Potassium Alkoxides Research Articles

ChemInform Abstract: An Alternative Approach to Differentially Substituted 2‐Oxazoline Chalcogen Derivatives.

In this study we present an alternative method to obtain several substituted mono or bis-2-oxazolines containing a chalcogen atom as a tether element. Alkylation of 2-tosyloximethylene-2-oxazoline with an appropriate sodium, lithium or potassium alkoxide yielded the corresponding ether. Introduction of sulfur or selenium was easily accomplished using the corresponding sodium salts. The 77Se NMR for alkyl or aryl 2-methylene-2-oxazoline selenides shows good correlation with the electronegativity pattern of substituents. Most products containing oxazolinyl-chalcogen were stable under the usual experimental conditions. However, the tellurium derivatives showed unusual sensitivity to light and oxygen, decomposing through a very complex mechanistic pathway. As a result of this oxidative process, 4,4-dimethyl-2-oxazoline-2-carbaldehyde could be isolated and fully characterized for the first time, in 17% yield.

Azeotrope enabled polymerization of ethylene oxide

We report a synthetic route for poly(ethylene oxide) (PEO) using azeotropic distillation to remove water and drive the equilibrium of an alkyl hydroxide and potassium hydroxide to potassium alkoxide, avoiding the use of pyrophoric organometallics.

ChemInform Abstract: Z‐Selective, anti‐Markovnikov Addition of Alkoxides to Terminal Alkynes: An Electron Transfer Pathway?

AbstractN,N′‐dimethylethylenediamine enhances the diastereoselective addition of potassium alkoxides to aryl alkynes to yield enol ethers.

An alternative approach to differentially substituted 2-oxazoline chalcogen derivatives

In this study we present an alternative method to obtain several substituted mono or bis-2-oxazolines containing a chalcogen atom as a tether element. Alkylation of 2-tosyloximethylene-2-oxazoline with an appropriate sodium, lithium or potassium alkoxide yielded the corresponding ether. Introduction of sulfur or selenium was easily accomplished using the corresponding sodium salts. The 77Se NMR for alkyl or aryl 2-methylene-2-oxazoline selenides shows good correlation with the electronegativity pattern of substituents. Most products containing oxazolinyl-chalcogen were stable under the usual experimental conditions. However, the tellurium derivatives showed unusual sensitivity to light and oxygen, decomposing through a very complex mechanistic pathway. As a result of this oxidative process, 4,4-dimethyl-2-oxazoline-2-carbaldehyde could be isolated and fully characterized for the first time, in 17% yield.

ChemInform Abstract: A Direct C—H Arylation of Unactivated Arenes Promoted by Mixed Potassium Alkoxides.

AbstractThe use of mixed alkoxides as base is the key to success for the direct arylation of benzene with aryl iodides.

Z-selective, anti-Markovnikov addition of alkoxides to terminal alkynes: an electron transfer pathway?

Potassium alkoxides undergo anti-Markovnikov addition to aryl-substituted alkynes with Z selectivity in DMF as the solvent. The yields and efficiency of the reaction was also found to be enhanced by the addition of a secondary amine ligand such as N,N′-dimethylethylenediamine. Mechanistic investigations suggest that the products, reaction rates and selectivity can be explained via a single electron transfer from the alkoxide to the alkyne. This leads to a radical anion intermediate, which then rapidly combines with the alkoxide to yield a vinyl anion whose lifetime governs the E:Z selectivity observed in the products.

A Direct CH Arylation of Unactivated Arenes Promoted by Mixed Potassium Alkoxides

AbstractAn intermolecular CH arylation of unactivated arenes with aryl iodides is made viable through a transition‐metal‐free approach. This simple and efficient process obviates the common use of diamines or diols as the promoters. With the aid of only mixed potassium alkoxides, a number of unactivated arene CH bonds can be directly arylated through a homolytic aromatic substitution (HAS) pathway.

Synthesis of 7-iodo(arylsulfanyl)methyl-7,8-dihydro-[1,3]thiazolo[2,3-i]purinium pentaiodide (perchlorates) and their transformation into 4-amino-5-(1,3-thiazol-2-yl)imidazole derivatives

Intramolecular electrophilic cyclization of 6-allylsulfanylpurine by the action of iodine and arenesulfenyl chlorides gave 7-iodomethyl-7,8-dihydro[1,3]thiazolo[2,3-i]purin-6-ium pentaiodide and 7-arylsulfanylmethyl-7,8-dihydro[1,3]thiazolo[2,3-i]purin-6-ium perchlorates, respectively. 7-Iodomethyl-7,8-dihydro-[1,3]thiazolo[2,3-i]purin-6-ium iodide reacted with sodium and potassium alkoxides to produce alkyl N-[5-(4-methyl-1,3-thiazol-2-yl)-1H-imidazol-4-yl]formimidates, and its reaction with secondary cyclic amines afforded 5-(4-methyl-1,3-thiazol-2-yl)-N-[morpholin-4-yl(or piperidin-1-yl)methylidene]-1H-imidazol-4-amines. Successive treatment of 7-arylsulfanylmethyl-7,8-dihydro[1,3]thiazolo[2,3-i]purin-6-ium perchlorates with sodium acetate and morpholine led to the formation of 5-(4-arylsulfanylmethyl-4,5-dihydro-1,3-thiazol-2-yl)-N-(morpholin-4-ylmethylidene)-1H-imidazol-4-amines.

Living Anionic Polymerization of 1,4-Divinylbenzene and Its Isomers

The anionic polymerization of 1,4-divinylbenzene (1) and its ortho (2) and meta isomers (3) were studied under a variety of conditions. One of the two vinyl groups of 1 was selectively and exclusively polymerized in a living manner by the addition of a suitable additive under the conditions of −78 °C for 1 min and −95 °C for 30 min. Under such conditions, the unwanted addition reaction of the chain-end anion to the pendant vinyl group was almost suppressed and soluble polymers with predictable molecular weights of up to 60 500 g/mol and narrow molecular weight distributions (Mw/Mn < 1.05) were quantitatively obtained. The amount of dimerized chain produced by the addition reaction was negligible or very small (<5%). The effective additives in the polymerization involve potassium alkoxides and phenoxides, derived from tert-butyl alcohol, sec-butyl alcohol, 2,4-dimethyl-3-pentanol, 1-methylcyclohexanol, 1:2,5:6-di-O-isopropylidene-α-d-glucofuranose, phenol, 1-naphthol, and 2,6-di(tert-butyl)-4-methylphenol,...

A Theoretical Study of Cyclohexyne Addition to Carbonyl–Cα Bonds: Allowed and Forbidden Electrocyclic and Nonpericyclic Ring-Openings of Strained Cyclobutenes

The mechanism of cyclohexyne insertion into a C(O)-C(α) bond of cyclic ketones, explored experimentally by the Carreira group, has been investigated using density functional theory. B3LYP and M06-2X calculations were performed in both gas phase and THF (CPCM, UAKS radii). The reaction proceeds through a stepwise [2 + 2] cycloaddition of cyclohexyne to the enolate, followed by three disparate ring-opening possibilities of the cyclobutene alkoxide to give the product: (1) thermally allowed conrotatory electrocyclic ring-opening, (2) thermally forbidden disrotatory electrocyclic ring-opening, or (3) nonpericyclic C-C bond cleavage. Our computational results for the model alkoxide and potassium alkoxide systems show that the thermally allowed electrocyclic ring-opening pathway is favored by less than 1 kcal/mol. In more complex systems containing a potassium alkoxide (e-f), the barrier of the allowed conrotatory ring-opening is disfavored by 4-8 kcal/mol. This suggests that the thermodynamically more stable disrotatory product can be formed directly through a "forbidden" pathway. Analysis of geometrical parameters and atomic charges throughout the ring-opening pathways provides evidence for a nonpericyclic C-C bond cleavage, rather than a thermally forbidden disrotatory ring-opening. A true forbidden disrotatory ring-opening transition structure was computed for the cyclobutene alcohol; however, it was 19 kcal/mol higher in energy than the allowed conrotatory transition structure. An alternate mechanism in which the disrotatory product forms via isomerization of the conrotatory product was also explored for the alkoxide and potassium alkoxide systems.

Lithium and potassium aminoalkoxides

The structures of the Group 1 metal aminoalkoxides Li[OCH(CH 2 CNMe 2 ) 2 ] ( 1 ) and K[OCH(CH 2 CNMe 2 ) 2 ]∙HOCH(CH 2 CNMe 2 ) 2 ( 2 ) have been determined. 1 is a hexa­meric drum in which two Li 3 O 3 rings are joined co-facially, whereas 2 is tetrameric and adopts a K 4 O 4 ladder structure, novel for homoleptic potassium alkoxides.

Synthetic scope, computational chemistry and mechanism of a base induced 5- endo cyclization of benzyl alkynyl sulfides

We present an experimental and computational study of the reaction of aryl substituted benzyl 1-alkynyl sulfides with potassium alkoxide in acetonitrile, which produces 2-aryl 2,3-dihydrothiophenes in poor to good yields. The cyclization is most efficient with electron withdrawing groups on the aromatic ring. Evidence indicates there is rapid exchange of protons and tautomerism of the alkynyl unit prior to cyclization. Theoretical calculations were also conducted to help rationalize the base induced 5- endo cyclization of benzyl 1-propynyl sulfide ( 1a). The potential energy surface was calculated for the formation of 2,3-dihydrothiophene in a reaction of benzyl 1-propynyl sulfide ( 1a) with potassium methoxide. Geometries were optimized with CAM-B3LYP/6-311+G(d,p) in acetonitrile with the CPCM solvent model. It is significant that the benzyl propa-1,2-dien-1-yl sulfane ( 6) possessed a lower benzylic proton affinity than the benzyl prop-2-yn-1-yl sulfane ( 8) thus favoring the base induced reaction of the former. From benzyl(propa-1,2-dien-1-yl sulfane ( 6), 2,3-dihydrothiophene can be formed via a conjugate base that undergoes 5- endo- trig cyclization followed by a protonation step.

Random low vinyl styrene–isoprene copolymers

The present work is to the syntheses and characterization of random, low vinyl copolymers containing styrene and isoprene (SIR’s). The content of these SIR’s ranged from 10% styrene/90% isoprene to 60% styrene/40% isoprene, and all were soluble in hexane solvent. The anionic polymerization of these SIR’s was initiated by a catalyst system of various sodium dodecylbenzene sulfonate (SDBS) to n-butyllithium ( n-BuLi) ratios. The SDBS allowed for styrene to become randomly incorporated onto the polyisoprene chain without any increase in the 3,4-unit of the isoprene. The glass transition temperature of the resulting polymers could be controlled by the styrene content and microstructure (blocky versus random) in the polymer chain. Kinetic data confirmed that styrene and isoprene have similar reaction kinetics. NMR and ozonolysis confirmed that random, low vinyl SIR’s were indeed being synthesized. The unique features of this system are that it does not metallate the polymers as was seen in the previous publication using the sodium and potassium alkoxides. Molecular weight differences due to SDBS are discussed. Finally, rubber process analyzer (RPA) results were presented for various styrenes content SIR’s.

Synthesis of polysiloxaneurethane polymers by the aromatic isocyanate-activated opening of the octamethyltetrasiloxane ring via an anionic mechanism

Here, we present the results of the study of the interaction in the octamethylcyclotetrasiloxane-aromatic isocyanate-open coupling analogues system of crown ethers containing terminal hydroxyl and potassium alkoxide groups. It was found that the involvement of the organosiloxane cycle in the polymerization process precedes the opening of the isocyanate groups on the carbonyl component. It is shown that the formation of transverse cross-linking bonds in the polymer formation system is caused by the parallel reaction of cyclotrimerization. It is found that the ratio of the reaction rate constants of the copolymerization and the parallel reactions of cyclotrimerization and urethane formation depend on the synthesis temperature.

Synthesis of aluminium complexes bearing a piperazine-based ligand system

Aluminium complexes bearing the N, N-chelating ligand 1,4-bis(2-hydroxy-3,5-di- tert-butyl)piperazine ( 1) have been synthesised. Both monometallic and bimetallic aluminium methyl complexes ( 2 and 3, respectively) were prepared by treatment of 1 with the appropriate amount of AlMe 3. Complex 2 can be converted to 3 by addition of excess AlMe 3. Bimetallic aluminium-ethyl complex 4 was also prepared. Treatment of 1 with AlEt 2Cl afforded the monometallic chloride complex 5. Treatment of this latter complex with potassium alkoxides (KOR, R = Me, Et, i Pr, t Bu) or AgOTf afforded the corresponding aluminium alkoxide complexes ( 6, R = Et; 7, R = Me; 8, R = i Pr; 9, R = t Bu; 10, R = OTf) in good yields. Aluminium ethoxide complex 6 was also synthesised by treatment of 1 with AlEt 2OEt. All of these complexes were tested as potential catalysts in the ring-opening polymerisation of rac-lactide and caprolactone with limited success.

Highly efficient synthesis of functionalized tertiary alcohols catalyzed by potassium alkoxide–crown ether complexes

A highly efficient Mukaiyama aldol reaction between ketones and trimethylsilyl enolates in the presence of potassium alkoxide–crown ether complexes as Lewis base catalysts (0.3–5 mol %), which minimized the competing retro-aldol reaction, was developed. These catalysts promoted other addition reactions of trimethylsilyl reagents to ketones and aldimines, such as silyltrifluoromethylation, silylcyanation, and silylphosphonylation. A direct hydrophosphonylation of ketones also proceeded when the catalysts were used as a Brønsted base under mild reaction conditions.

A novel optically active diblock copolymer composed of poly(ethylene glycol) and poly[N‐{o‐(4‐phenyl‐4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenyl}maleimide]: Synthesis, micellization behavior, and chiroptical property

AbstractA series of optically active amphiphilic block copolymers were synthesizedby using potassium alkoxide of poly(ethylene glycol) monomethyl ether (MeOPEGO−K+) to initiate the anionic polymerization of N‐{o‐(4‐phenyl‐4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenyl}maleimide [(R)‐PhOPMI]. The PEG‐macroinitiators generated in situ in the reaction between MeOPEGOH and potassium naphthylide in tetrahydrofuran. The synthetic procedure may provide the PEG‐b‐PPhOPMI copolymers with well‐defined structure, as evidenced by gel permeation chromatography, 1H NMR, FTIR, and elemental analysis. In particular, the preparation of block copolymers having a laevorotation or dextrorotation activity was accomplished by changing the feed composition. The micellization was examined for the amphiphilic block copolymers in aqueous milieu by fluorescence spectroscopy, dynamic light scattering, and circular dichroism. The results indicate that the copolymers could form regular spherical micelles with core‐shell structure when the hydrophilic component was long enough; in contrast, the copolymers containing shorter PEG segments formed aggregates in large dimension due to the considerable interaction between hydrophobic PPhOPMI components. Also, it was found that the aggregated structure of the polymeric micelles is strongly dependent on the medium nature and the polymer concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1025–1033, 2008

Potassium Hydroxide and Potassium Alkoxides

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Alkali Metal Counterion Control of Enolate Protonation Stereoselectivity

[reaction: see text] Generation of the lithium salt of the norbornenol shown (M = H) followed by quenching with aqueous NH(4)Cl solution gives predominantly the beta-epimeric ketone 6. Similar production of the potassium alkoxide leads instead to the alpha-epimer (99:1). These results reveal the potential importance of alkali metal counterions as stereocontrol elements.

Dienes polymerization in the presence of metal hydrides and triethylaluminum

Butadiene and isoprene can be polymerized by potassium hydride in aromatic hydrocarbons at various temperatures and in short times. A first additive, triethylaluminum, is needed to favour the homogeneity of the initiating system in the solvent of reaction. The importance of a second additive, a potassium alkoxide, is discussed in terms of activation of the polymerization. Experimental parameters like temperature, initiator concentration, activator/initiator ratio and monomer concentration are also investigated with the aim to reach a high content of 1,4 units. Transfer reactions occur for isoprene even though a good control of the polymerization is obtained for butadiene.