Metallo esters. VII. Stabilizing effect of sodium tert-butoxide on the growth center in the anionic polymerization of methacrylic esters

The growth center in the anionic polymerization of methacrylic esters is stabilized with alkaline alkoxides, sodium tert-butoxide in particular. The lifetime of the growth center was investigated in the polymerization of methyl methacrylate by evaluating yield and molecular weight distribution of the polymer formed when the monomer was added in two doses. The average lifetime of the original growth center stabilized by sodium tert-butoxide at 20°C under the given conditions was longer than several minutes. The stabilization of the growth center was also used in the stepwise copolymerization of n-butyl methacrylate and methyl methacrylate. The copolymer thus obtained in high yield was characterized as a block copolymer on the basis of its solubility, nuclear magnetic resonance (NMR) spectra, and measurements of the complex shear modulus.     

Experimental and Quantum Chemical Studies of 2-Phosphinylphenol Derivatives

Carbon-oxygen bonds ortho to a phosphoryl group in triarylphosphine oxides undergo cleavage when the oxides are either fused with potassium hydroxide or treated with potassium tert-butoxide in refluxing toluene, presumably through a nucleophilic addition-elimination mechanism. Thus, bis(2-hydroxyphenyl)phenylphosphine oxide is produced along with the expected 2-phenoxyphenyl(phenyl)phosphinic acid from 10-phenyl-10H-phenoxaphosphine 10-oxide. The latter starting material is also produced, together with bis(2-hydroxyphenyl)phenylphosphine oxide, when bis(2-methoxyphenyl)phenylphosphine oxide is fused with potassium hydroxide. Fusion of bis(2-methoxyphenyl)phenylphosphine oxide with sodium hydroxide, however, yields 2-hydroxyphenyl(phenyl)phosphinic acid. Ab initio quantum chemical studies confirm that the downfield ³¹P chemical shift that is observed in 2-phosphinylphenols is due to hydrogen bonding to the phosphoryl group.     

Synthesis of a New Series of Imidazo-[1,5-a]pyrido[2,3-e]pyrazines as Potential Ligands for the GABA Receptor Complex

Summary.  Starting from 2-chloro-3-nitropyridine, 2-isopropyl-1,4-dihydropyrido[2,3-b]pyrazin-2(3H),3-dione was synthesized. This compound was reacted with potassium tert-butoxide and diethyl chlorophosphate to afford an intermediate dihydropyrido[2,3-b]pyrazin-2-ylphosphate derivative which in turn furnished the desired 1,2,4-oxadiazolylimidazo[1,5-a]pyrido[2,3-e]pyrazine derivatives with 5-alkyl-3-isocyanomethyl-1,2,4-oxadiazoles in the presence of additional tert-butoxide. The title compounds are potential ligands for the γ-aminobutyric acid A/benzodiazepine receptor complex. Received November 26, 2001. Accepted December 3, 2001     

EXAFS study of zirconium alkoxides as precursors in the sol-gel process: II. The influence of the chemical modification

EXAFS studies of primary zirconium alkoxides Zr(OR)₄ with OR = n-propoxide and n-butoxide, dissolved in their corresponding alcohols and chemically modified with acetylacetone (Hacac) and acetic acid (HOAc) in different molal ratios, are presented. The EXAFS-spectroscopic results, supported by FT-IR-studies, indicate a different chemical behavior of the complexing agents. In contrast to acetylacetone, the addition of acetic acid does not change the oligomeric structure of the zirconium alkoxides. Amazingly, the modification with acetic acid leads, in comparison to the pure compounds, to a shortened metal centre distance, whereas in the reaction with acetylacetone the Zr-Zr distance is not changed. With the determined distances and a rough quantitative inclusion of the coordination numbers it was possible to deduce detailed structure models.     

Use of Potassium tert-Butoxide to Increase the Nucleophilicity of an Imine Stabilized o-Tolyl Lithium Derivative

Addition of a solution of potassium tert-butoxide in THF to a mixture of LDA and an o-tolylimine caused the resultant anion to be alkylated quickly by the relatively unreactive l-chloro-7-phenylheptane. Significant β-elimination to 7-phenylhepta-1-ene did not occur.     

Trifluoroacetophenone as nucleophilic trifluoromethylating reagent

Trifluoroacetophenone can be used as nucleophilic trifluoromethylating reagent towards non-enolizable ketones by action of potassium tert-butoxide.     

ABOUT THE REACTION OF 2,3-DIBROMO-2-METHYL-N-(1-ADAMANTYL)-PROPANAMIDE WITH SODIUM TERT-BUTOXIDE. A COMPETITION EXPERIMENT

2,3-Dibromo-2-methyl-N-(1-adamantyl)propanamide (4), a precursor equally suited for the preparation of an α-lactam and a β-lactam, upon treatment with sodium tert-butoxide ether gives no α-lactam (5), but an excellent yield of the isomeric β-lactam, 1-(1-adamantyl)-3-bromo-3-methylazetidinone (6) as the only product. Repeating the experiment using a large excess of sodium tert-butoxide still leads to β-lactam 6 in 76.1% yield, but now accompanied by its dehydrobrominated derivative, β-lactam 7, in 17.4% yield, and no trace of α-lactam 5     

A Facile Synthesis of Vinyl and Allylic 2,2,2-Trifluoroethyl Phosphonates

Condensation of several representative aldehydes with the anion derived from tetrakis(2,2,2-trifluoroethyl) methylenediphosphonate, a new Wadsworth-Emmons reagent, afforded (Z)-vinyl phosphonates in good yields. The latter, when treated with a catalytic amount of potassium tert-butoxide in DMSO isomerized to the corresponding (E)-allylic phosphonates, which produce E,Z-dienes when reacted with a second aldehyde.     

Synthesis of fluoro and trifluoromethyl derivatives of 2-phenylquinolin-4-ol

A tert-butoxide base-mediated cyclization of fluoro- and trifluoromethyl-substituted Schiff bases 12-19 produces 4-tert-butoxyquinolines 23-30 which are hydrolyzed to quinolin-4-ols 31-38 .     

Dehydrogenation of the NH−NH Bond Triggered by Potassium tert-Butoxide in Liquid Ammonia

A novel strategy for the dehydrogenation of the NH−NH bond is disclosed using potassium tert-butoxide (tBuOK) in liquid ammonia (NH₃) under air at room temperature. Its synthetic value is well demonstrated by the highly efficient synthesis of aromatic azo compounds (up to 100 % yield, 3 min), heterocyclic azo compounds, and dehydrazination of phenylhydrazine. The broad application of this strategy and its benefit to chemical biology is proved by a novel, convenient, one-pot synthesis of aliphatic diazirines, which are important photoreactive agents for photoaffinity labeling.     

Facile Synthesis of Aryl‐Pyridyl,Pyridazinyl, Pyrazinyl,and Triazinyl Acetonitriles

Dihalo pyridine, pyrazine, and pyridazine analogues were converted to the corresponding monohalo acetonitrile analogues through nucleophilic displacement of the halogen with the anion of tert‐butyl cyanoacetate. The monohalo acetonitriles reacted under Suzuki or Stille conditions to form the title compounds.     

Combining Neopentyllithium with Potassium tert‐Butoxide: Formation of an Alkane‐Soluble Lochmann–Schlosser Superbase

Mixtures of alkyllithium and heavier alkali‐metal alkoxides are often used to form alkyl compounds of heavier alkali metals, but these mixtures are also known for their high reactivity in deprotonative metalation reactions. These organometallic mixtures are often called LiC–KOR superbases, but despite many efforts their constitution remains unknown. Herein we present mixed alkali‐metal alkyl/alkoxy compounds produced by reaction of neopentyllithium with potassium tert‐butoxide. The key to success was the good solubility and temperature‐stability of neopentyl alkali‐metal compounds, leading to hexane‐soluble mixtures, which allowed handling at ambient temperatures and isolation by crystallization. The compounds in solid state and in solution were identified by X‐ray crystallography and NMR spectroscopy as mixtures of lithium/potassium neopentyl/tert‐butoxy aggregates of varying compositions Li_xK_yNp_z(OtBu)_x+y?z.     

Synthesis of substituted pyrido[3´,2´:4,5]thieno[3,2-c]isoquinolin-5(6H)-ones and their sulfinyl and sulfonyl derivatives

A method for the synthesis of previously unknown pyrido[3´,2´:4,5]thieno[3,2-c]isoquinolin-5(6H)-ones was suggested, which includes a condensation reaction of substituted 3-cyanopyridine-2(1H)-thiones with methyl 2-(chloromethyl)benzoate and subsequent treatment of the condensation products with potassium tert-butoxide. The oxidation of the condensation products to sulfoxides or sulfones and subsequent treatment of these compounds with potassium tert-butoxide led to substituted pyrido[3´,2´:4,5]thieno[3,2-c]isoquinolin-5(6H)-one 11-oxides or substituted pyrido[3´,2´:4,5]thieno[3,2-c]isoquinolin-5(6H)-one 11,11-dioxides.

     

Intramolecular Cyclization of Furfuryl 2-Propynyl Ether

Intramolecular cyclization of furfuryl 2-propynyl ether in the presence of a catalytic amount ofpotassium tert-butoxide in tert-butyl alcohol gives 3a'6-epoxy-1'3-dihydro-6H-isobenzofuran. The cyclizationis presumed to be favored by preliminary isomerization of the 2-propynyl group into allenyl. Heating of thecyclization product with excess potassium tert-butoxide in tert-butyl alcohol results in cleavage of the epoxybridge with formation of 6-hydroxy-1'3-dihydroisobenzofuran.     

Alkoxide-induced reactions of N-substituted saccharins. Synthesis of 1,2-benzothiazocine 1,1-dioxide and 2,3-dihydropyrrolo[1,2-b]-[1,2]benzisothiazole 5,5-dioxide derivatives

The reactions of saccharin derivatives 1 with sodium alkoxides were studied. Under mild conditions, compounds 1a-f gave the corresponding open sulfonamides 5a-f . Under drastic conditions, β-(saccharin-2)propionic acid derivatives 1a,b reacted with sodium ethoxide affording saccharin and β-ethoxypropionic acid derivatives 4a,b . γ-(Saccharin-2)butyric acid derivatives 1c,d and γ-(saccharin-2)-butyrophenone 1f reacted with sodium t-butoxide in dimethyl sulfoxide affording 5-substituted 6-hydroxy-3,4-dihydro-2H-1,2-benzothiazocine 1,1-dioxides 9 . From mother liquors, 1-substituted 2,3-dihydro-pyrrolo[1,2-b][1,2]benzisothiazole 5,5-dioxides 10 were isolated several hours later, though not detected immediately after completing the reaction. When the reactions were carried out in t-butyl alcohol, the yields of 9 diminished and those of 10 increased with product ratio inversion. Different experimental observations on the possible pathway generating 9 and 10 are discussed.     

Studies on the Chemistry of Thienoannelated O , N - and S , N -Containing Heterocycles, 28 [1]. Synthesis of Imidazo[1,5- d ]thieno[2,3- b ][1,4]thiazine Derivatives as GABA -Receptor Ligands

 GABA-receptor-ligands are still very interesting in drug-development. Usually benzodiazepines are used in the treatment but they have serious side-effects. Thus, a recently synthesized quioxaline derivative which showed reduced side-effects in an animal model was used as a model-substance. The cyclus was modified to optimize the pharmacological profile. Accordingly, a series of imidazo-thieno-thiazines was synthesized starting from 5-acetyl-2-chloro-3-nitrothiophene to yield 6-ethyl-2,3-dihydro-1H-thieno[2,3-b][1,4]thiazine-2-one. Reaction with potassium tert-butoxide and diethylchlorophosphate gave an intermediate, which resulted in the desired ring system after adding the corresponding isocyanides and potassium tert-butoxide.     

THF-solvated Heavy Alkali Metal Benzyl Compounds (Na,Rb, Cs): Defined Deprotonation Reagents for Alkali Metal Mediation Chemistry

The incorporation of heavy alkali metals into substrates is both challenging and essential for many reactions. Here, we report the formation of THF-solvated alkali metal benzyl compounds [PhCH₂M ⋅ (thf)_n] (M=Na, Rb, Cs). The synthesis was carried out by deprotonation of toluene with the bimetallic mixture n-butyllithium/alkali metal tert-butoxide and selective crystallization from THF of the defined benzyl compounds. Insights into the molecular structure in the solid as well as in solution state are gained by single crystal X-ray experiments and NMR spectroscopic studies. The compounds could be successfully used as alkali metal mediating reagents. The example of caesium showed the convenient use by deprotonating acidic C−H as well as N−H compounds to gain insight into the aminometalation using these reagents.     

Studies on the Chemistry of Thienoannelated O , N - and S , N -Containing Heterocycles, 28 [1]. Synthesis of Imidazo[1,5- d ]thieno[2,3- b ][1,4]thiazine Derivatives as GABA -Receptor Ligands

Summary.  GABA-receptor-ligands are still very interesting in drug-development. Usually benzodiazepines are used in the treatment but they have serious side-effects. Thus, a recently synthesized quioxaline derivative which showed reduced side-effects in an animal model was used as a model-substance. The cyclus was modified to optimize the pharmacological profile. Accordingly, a series of imidazo-thieno-thiazines was synthesized starting from 5-acetyl-2-chloro-3-nitrothiophene to yield 6-ethyl-2,3-dihydro-1H-thieno[2,3-b][1,4]thiazine-2-one. Reaction with potassium tert-butoxide and diethylchlorophosphate gave an intermediate, which resulted in the desired ring system after adding the corresponding isocyanides and potassium tert-butoxide. Corresponding author. E-mail: thomas.erker@univie.ac.at Received August 6, 2002; accepted August 13, 2002     

Synthesis of new binuclear ferrocenyl compounds by hydrosilylation reactions

Ferrocenyl silanes are prepared by treatment of Grignard reagents produced from 4-chlorobutylferrocene derivatives and chlorodimethylsilane in THF. Butenylferrocenes are prepared by the elimination reaction of 4-chlorobutylalkylferrocenes by sodium tert-butoxide in DMSO. A hydrosilylation reaction between a butenyl compound and ferrocenylsilane occurred in dry toluene at room temperature in the presence of the Karstedt catalyst to produce the desired binuclear ferrocenyl compound in good to high yields. The electrochemical behavior of new ferrocenyl compounds were studied by cyclic voltammetry in CH₃CN/0.1 M LiClO₄, and the relation between the peak currents and the square root of the scan rate, showed that the redox process is diffusion-limited.     

The Preparation and X-Ray Structure of [AsPh4][Ph2P(S)NSiMe3] · 0.5 THF

The reaction of Ph₂P(S)N(SiMe₃)₂ with potassium tert-butoxide in a 1:1 molar ratio produces K[Ph₂P(S)NSiMe₃], which was converted to the AsPh₄⁺ salt by metathesis with [AsPh₄]Cl. The X-ray crystal structure of [AsPh₄][Ph₂P(S)NSiMe₃] · 0.5 THF consists of noninteracting AsPh₄⁺ and Ph₂P(S)NSiMe₃^? ions with d(P? S) = 1.980(4) Å and d(P? N) = 1.555(8) Å. The PNSi bite angle in the anion is 136.3(5)°. Electrophilic attack by Ph₂P(S)Cl occurs at the sulfur atom of Ph₂P(S)NSiMe₃^?. The oxidation of the anion with iodine produces a disulfide which regenerates K[Ph₂P(S)NSiMe₂] upon treatment with potassium tert-butoxide.