Cycloaddition von phenylarsinen an pentadiin-1,4-one-3 und 3-methylenpentadiine-1,4: Elektrocyclische reaktionen von 2,3-bis-methylen-arsolenen-4

The radicalic cycloaddition of phenylarsine and trimethylsilylsubstituted phenylarsines to pentadiyn-1,4-ones-3 yields the 2-methylene-arsolene-4-ones-3; these ketones react with diphenylketene to give the substituted 2,3-bis-methylene-arsolenes-4, which undergo thermal electrocyclic reactions. The resulting benzannelated arsolenes are dehydrogenated to the corresponding arsoles, which can be isolated by reaction of phenylarsine with 3-diphenylmethylene-pentadiynes-1,4-directly.     

Pentadienylsilanes as new reagents of the siteselective dienylmethylation of electrophiles promoted by a Lewis acid

(2,4-Pentadienyl)- and (2,4-hexadienyl)trimethylsilanes, prepared from the corresponding pentadienylpotassiums and trimethylchlorosilane, react smoothly with various electrophiles such as acetals, aldehydes and acid halides to give pentadienylation products, with regiospecific transposition of the pentadienyl group.     

Reactions of ketene acetals—IX: The synthesis of naphthoquinones from benzoquinones

Halogenobenzoquinones react with ketene acetals and give benzofurans, but in the presence of acetic acid, naphthoquinones are produced in variable yields. Some aspects of the reaction have been studied and the method has been applied to the synthesis of useful intermediates and of derivatives of some naturally occurring naphthoquinones such as tri-O-methylflaviolin 20 and tetra-O-methylspinochrome B23. Benzoquinones also react with conjugated ketene acetals without acid catalysis, providing convenient syntheses of ramentaceone 43, O-methylstypandrone 45 and 1,3,6,8-tetramethoxyanthraquinone 34.     

Hydrozirconation of stannylacetylenes. Synthesis and reactions of ketene Stannyl(Telluro) acetals

Stannylacetylenes 7a-e react with Cp(2)Zr(H)Cl in THF at room temperature to give the alpha-zirconated vinylstannane intermediates 8a-e, which subsequently react with butyltellurenyl bromide (2.0 equiv) to give exclusively ketene stannyl(telluro) acetals 6a-e of E configuration. Similar reactions were performed using phenylselenenyl bromide (2.0 equiv) as the electrophile, but a mixture of products was formed including the expected ketene stannyl(seleno) acetals 12. Otherwise, the use of 1.4 equiv of Cp(2)Zr(H)Cl and 1.0 equiv of PhSeBr results in the exclusive formation of 12, in good yields. Treatment of ketene stannyl(telluro) acetals with iodine or NBS followed by reductive dehalogenation results in the formation of 1-iodo-1-telluroalkenes 4a-e and 1-bromo-1-telluroalkenes 5a-e, respectively, with total retention of the configuration.     

Reactions of 2-Butylsulfanyl-2-alkenals with Alcohols and Water

2-Butylsulfanyl-2-alkenals react with alcohols at room temperature in the presence of acid catalysts to give 45–90% of the corresponding acetals. Acetals derived from 2-butylsulfanylpropenal readily undergo hydrolysis at the vinylsulfanyl group (20°C, catalysis by HCl or TsOH) with formation of 2-oxopropionaldehyde O,O- or O,S-acetals in 70–90% yield. Unlike 2-butylsulfanyl-2-propenal O,O-dialkyl acetals, the initial aldehydes and 2,4-dinitrophenylhydrazones derived therefrom are stable to hydrolysis under analogous conditions: the vinyl sulfide moiety remains unchanged even under considerably more severe conditions (100°C, 3 h; HCl, H₂SO₄, CF₃SO₂OH, or TiCl₄).__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 6, 2005, pp. 832–836.Original Russian Text Copyright © 2005 by Keiko, Chuvashev, Stepanova, Larina.     

A simple TiCl4 promoted arylation of orthoformate and benzyl ethers by N,N-dialkylarylamines

N,N-Dialkylarylamines react with trimethyl orthoformate and TiCl₄ under ambient conditions to give the corresponding formyl derivatives in 75-89% yields, whereas the corresponding arylated products are obtained from benzyl ethers and acetals in 42-78% yields.     

Bocdene and mocdene derivatives of catechols and catecholamines

[reaction in text] Catechols react chemoselectively, in the presence of either alcohols, 1,2-diols, or simple phenols, with tert-butyl propynoate and with methyl propynoate to give 2-Boc-ethylidene (Bocdene) and 2-Moc-ethylidene (Mocdene) acetals, respectively, in 96-100% yields within 30 min at room temperature, provided that 150 mol % of DMAP is added. Cleavage of these acetals with pyrrolidine readily takes place (at room temperature!) in 95-100% yields. By taking advantage of the features of Bocdene acetals, novel catecholamine-related phosphate mimetics have been prepared.     

Microwave Irradiated Reactions of N-Phenacylpyridinium Chloride with Aromatic Aldehydes and Ketones

Pyridinium cations show a great variety of synthetic applications,due to the aromatic character of the pyridine heterocycle, to its basicity, and the electron-attracting influence of the nitrogen atom1-3. N-phenacylpyridium bromide in the presence of base…     

Preparation of cyclic ether acetals from 2-benzenesulphonylderivatives: a new mild glycosidation procedure

Several alcohols ranging from hindered to those containing chemicallysensitive groups react with 2-benzenesulphonyl cyclic ethers in the presence of magnesium bromide etherate and sodium bicarbonate to give good yields of the corresponding acetals.     

New protecting groups for 1,2-diols (boc- and moc-ethylidene). Cleavage of acetals with bases

[reaction: see text] 1,2-Diols react at rt with alkyl propynoates, in the presence of 4-dimethylaminopyridine, to give cyclic acetals which are quite stable to acid-catalyzed hydrolysis or methanolysis. 1,3-Diols and 1, 4-diols do not form acetals with alkyl propynoates under the same conditions. Deprotection is accomplished with bases (via elimination and addition/elimination steps).     

Nouvelle méthode de préparation d'éthers vinyliques à partir d'acétals

A new way to vinylic ethers from acetals Acetals react at low temperatures in presence of a Lewis acid (aluminium chloride or magnesium bromide) with tertiary amine to give in good yields the vinylic ethers corresponding to the elimination of one molecule of alcohol.     

Reactions with Stilbenes and Related Derivatives. Part I. Reactions of 1, 2-Dihalogeno-1, 2-bis-(4-methoxyphenyl)ethanes with Alcohols

The reaction of 1, 2-dibromo-1, 2-bis(4-methoxyphenyl)ethane with alcohols was associated with rearrangement to give the corresponding bis(4-methoxyphenyl)acetals. In boiling ethylene glycol 4,4′-dimethoxy-deoxybenzoin was also obtained due to an aldehyde-ketone rearrangement. 4,4′-Dimethoxybenzophenone was also formed being apparently derived from the acetals. The mechanism of formation of the acetals has been discussed.     

Reactions of t-butyl peresters—III Cuprous bromide-catalyzed reaction of peresters with ethers

Aliphatic and cyclic ethers react smoothly with t-butyl peracetate and t-butyl perbenzoate at 67–90° in the presence of cuprous bromide. The first products of this reaction are the acyloxy derivatives of the ethers, which are unstable under the chosen experimental conditions and decompose to the corresponding carboxylic acids and unsaturated ethers. Thus, 2,3-dihydrofuran was prepared from 2-benzoyloxytetrahydrofuran in a 66% yield. The unsaturated ethers add t-butyl alcohol to give the corresponding acetals, this step being catalyzed by the carboxylic acid. This reaction is general for ethers containing two adjacent methylene groups, such as n-propyl and n-butyl ethers, tetrahydrofuran, and tetrahydropyran. Diethers, such as 1,4-dioxane and 1,2-dimethoxyethane, give more stable benzoyloxy derivatives, which decompose slowly on prolonged heating to give the expected acetals in low yield.     

Reactions of Ketene Acetals V The Reaction with p-Benzoquinone Dihalides

2- or 3-Halonaphthoquinones are known to react with ketene dialkyl acetals and to yield 1,3-dialkoxyanthraquinones^2,3. Various p-benzoquinones on the other hand have given only 2-alkoxy-benzofurans². 3-Chloro-5,7-dimethoxy-1,4-naphthoquinone (4) and 1,3,6,8-tetramethoxyanthraquinone (10), important intermediates for the synthesis of naturally occurring quinones, have now been obtained under analogous conditions using p-benzoquinone dihalides (trans-5,6-dihalo 2-cyclohexene 1,4-diones). Compound 4 does not appear to have been described but is readily converted to 3,5,7-trimethoxy-1,4-naphthoquinone (7) and regiospecifically³ to 1,3,6,8-tetramethoxyanthraquinone. Although the yields obtained in the reactions of ketene acetals with quinone dihalides are low, compounds 7 and 10 have only been prepared until now by tedious means involving a large number of steps^4–8, or by the degradation of natural products^9,10.     

A novel synthesis of 5-fluorouracil derivatives having oxacycloalkane moieties

5-Fluorouracil derivatives having oxacycloalkane moieties were synthesized in good yields by the reaction of trimethylsilyloxyalkanal dialkyl acetals with 2,4-bis(trimethylsilyl)-5-fluorouracil in the presence of SnCl₄.     

Reactions of Sodium Enolates Derived from 6-Aryl-3,5,5-trimethyl-2,3,5,6-tetrahydropyrane-2,4-diones with Substituted Benzenesulfonyl Chlorides and Arenediazonium Salts

Sodium enolates derived from 6-aryl-3,5,5-trimethyl-2,3,5,6-tetrahydropyrane-2,4-diones react with substituted benzenesulfonyl chlorides to give the corresponding O-sulfonation products, 6-aryl-4-(4-R-phenylsulfonyloxy)-3,5,5-trimethyl-5,6-dihydropyrane-2-ones. Reactions of the title compounds with arenediazonium tetrafluoroborates afford 6-aryl-3-arylazo-3,5,5-trimethyl-2,3,5,6-tetrahydropyran-2,4-diones as mixtures of syn and anti isomers.     

Reaction of Acetals with Various Carbon Nucleophiles under Non‐Acidic Conditions: C?C Bond Formation via a Pyridinium‐Type Salt

Mild substitution reactions of acetals with carbon nucleophiles via the pyridinium‐type salts generated by the treatment of acetals with TESOTf‐2,4,6‐collidine or 2,2′‐bipyridyl have been developed. Various carbon nucleophiles, such as organocuprates, silyl enol ethers, enamines, etc., reacted with the pyridinium‐type salts to give the corresponding substituted products in good yields. The reactions proceeded under very mild conditions (non‐acidic conditions) and thus acid‐sensitive functional groups can be tolerated during the reaction. In addition, only an acetal can form the pyridinium‐type salt and react with nucleophiles in the presence of a ketal. This unusual selectivity is in contrast to general methods conducted under acidic conditions.     

Studies on organophosphorus compounds XLVIII Synthesis of Dithioesters from P,S-Containing Reagents and Carboxylic Acids and Their Derivatives

2,4-Bismethylthio-1,3,2,4-dithiadiphosphetane 2,4- disulfide, IIa, is prepared from 0,0-dimethyldithiophosphoric acid, Ia, and P₄S₁₀ at 160°C. 2,4-Bis(4-phenoxyphenyl)-1,3,2,4- dithiadiphsophetane 2,4-disulfide, IIc, and 2,4-bis(4-phenylthiolophenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide, IId, are prepared at l60°C from P₄ S₁₀ and diphenylether and diphenylsulfides, respectively. Carboxylic acids RCOOH(R = CH₃ C₂H₅, n-C₃H₇, n-C₄H₉, C₆H₅CH₂, C₆H₈) react with compound Ia at 130°C to give the corresponding methyl dithioesters. Carboxylic acids RCOOH (R = C₆H₈-CH₂, C₆H₈) react with compound Ib at 200°C for 15 min to give the corresponding ethyl dithioesters, while low boiling acids (R = CH₃, C₂H₈, n-C₃H₇) yielded mixtures of the corresponding ethyl dithioester and ethyl carboxylate. Carboxylic acid chlorides RCOCl (R = ClCH₂, C₂H₅, t-C₄H₅ C₆H₅CH₂, C₆H₅, P-NO₂C₆H₄) react with compound IIa at 80°C to give the corresponding methyl dithioesters in good yields. S-Substituted thioesters react with IIC at 85°C to give the corresponding dithioesters in good yields. Dihydro2(3H)-furanone, VI, and 5-methyl-2(3H)-furanone, VII, react with IIa at 80°C; to dihydro-2(3H)-thiophenethione, VIII and 2,2'-dithiobis(5-methyl thiophene),IX, respectively. Also XI reacts with IIa,IIc, and IId to give VIII in nearly quantitative yields.     

A class of new silylating agents. II. A highly reactive reagent for introduction of the trimethylsilyl group.

Trimethylsilyl enol ethers of pentane-2,4-dione and methyl acetoacetate react rapidly with alcohols at room temperature without the need for catalytic assistance to give high isolated yields of trimethylsilyl ethers.     

Fluoro-ketones. II Reactions of fluorocarbon grignards and copper compounds with perfluoroalkylacid fluorides

The reactions between C₆F₅MgBr (I), p-BrC₆F₄MgBr (X), C₆F₅Cu (XXI), p-HC₆F₄Cu (XXII) and p-BrC₆F₄Cu (XV) with primary and secondary perfluoroalkylether acid fluorides were studied. The Grignard compounds react very slowly with the secondary acid halides (R_fCF(CF₃C(O)F) whereby competing reactions cause undesirable by-products and reduction of ketone yields. Primary acid halides (R_fCF₂C(O)F) react much faster with C₆F₅MgBr to give the ketone in improved yields. The organocopper compound react with either primary or secondary acid halides to give the ketone in excellent yields with no by-product formation from competing secondary reactions. Solvent, type of organometallic reagent and primary versus secondary acid fluoride are variables that influence product yield and product distribution.