Preparation of silyl polyenol ethers by carbonyl olefination of silyl esters

Silyl enol ethers were produced by the carbonyl olefination of silyl esters with titanium carbene complexes generated by the desulfurizative titanation of thioacetals. The regioselective preparation of silyl dienol and trienol ethers has been achieved by using unsaturated silyl esters and thioacetals.     

Low temperature syntheses of thioketals from enol ethers and carbonyl compounds

A dithioacetalisation procedure at low temperature using TMSOTf as the promoter is described. This method proved highly efficient for unprecedented transprotection of ketone enol ethers and was successfully applied to polyfunctional sensitive substrates.     

Synthesis of diaryl ethers based on one-pot [3+3] cyclizations of 1,3-bis(silyl enol ethers)

Functionalized and sterically encumbered diaryl ethers were prepared by [3+3] cyclization of 1,3-bis(silyl enol ethers) with 2-aryloxy-3-(silyloxy)alk-2-en-1-ones.     

Tris(pentafluorophenyl)silyl enol ethers: synthesis and aldol reactions

Silyl enol ethers bearing three pentafluorophenyl groups at the silicon atom are described. These compounds undergo uncatalyzed aldol reactions with aliphatic, α,β-unsaturated, and aromatic aldehydes. The observed reactivity is analyzed in terms of the Lewis acidity of the silyl fragment.     

Synthesis of enol ethers from lactones using modified Julia olefination reagents: application to the preparation of tri- and tetrasubstituted exoglycals

A new route to substituted exoglycals from the corresponding lactones is described. The enol ethers synthesis via a modified Julia olefination of sugar-derived lactones is extended to substituted benzothiazolyl sulfones to furnish tri- and tetrasubstituted exoglycals.     

Synthesis of 6-(perfluoroalkyl)salicylates by [3+3] cyclization of 1,3-bis(silyl enol ethers) with 3-ethoxy-1-(perfluoroalkyl)prop-2-en-1-ones

6-(Perfluoroalkyl)salicylates were prepared by [3+3] cyclization of 1,3-bis(silyl enol ethers) with 3-ethoxy-1-(perfluoroalkyl)prop-2-en-1-ones.     

PMA-SiO2 catalyzed synthesis of β-keto enol ethers

An efficient conversion of β-diketones into corresponding β-keto enol ethers with catalytic amount of PMA-SiO2 has been achieved.     

Catalytic olefination of carbonyl compounds. Effect of the structure of the carbonyl compound on the reaction

The mechanism of the novel reaction of catalytic olefination of carbonyl compounds was studied. The reaction involves the transformation of hydrazones of aromatic aldehydes and ketones into the corresponding dichloroalkenes and symmetrical azines by the treatment with carbon tetrachloride in the presence of CuCl as a catalyst. The stability of intermediate diazoalkanes is the main factor determining the direction of the reaction. In the case of sufficiently stable diazoalkanes, other products can be formed under the reaction conditions along with the products of catalytic olefination.     

Synthesis of substituted aryl enol ethers

A facile route toward substituted aryl diarylvinyl ethers 4 is developed from CuI-mediated cross-coupling reaction of substituted phenols 2 with diarylvinyl bromides 3 in the presence of various bidentate-based ligands in DMF. Skeleton 3 is prepared by Yan’s bromomethylenation of diarylketones 1 with CHBr₃–TiCl₄–Mg in the co-solvent of DME and CH₂Cl₂. The synthetic route obtains moderate yields from the one-step operation and the key structure of 4k is confirmed by X-ray crystallographic analysis. The CADD docking experiments of 4k have been included.     

Iodine-catalyzed synthesis of β-keto enol ethers

The use of iodine, as a catalyst for the synthesis of β-keto enol ethers at room temperature is reported.     

Regioselective synthesis of 2-acetyl- and 2-alkoxycarbonyl-3-(trifluoromethyl)phenols by [3+3] cyclization of 1,3-bis-silyl enol ethers with 4-ethoxy- and 4-silyloxy-1,1,1-trifluoroalk-3-en-2-ones

2-Acetyl- and 2-alkoxycarbonyl-3-(trifluoromethyl)phenols were prepared by [3+3] cyclization of 1,3-bis-silyl enol ethers with 4-ethoxy- and 4-silyloxy-1,1,1-trifluoroalk-3-en-2-ones.     

Carbonyl olefination utilizing an alkyl halide-titanocene(II) system

Ketones, aldehydes, esters and lactones are transformed into olefins by treatment with the organotitanium species formed from alkyl halides and titanocene(II).     

Synthesis of phthalates and isophthalates by [3+3] cyclizations of 1,3-bis(silyl enol ethers) with 3-(silyloxy)alk-2-en-1-ones

3-Hydroxyphthalates and 4-hydroxyisophthalates were prepared by sequential [3+3] cyclization reactions of 1,3-bis(silyl enol ethers) with 2- and 3-alkoxycarbonyl-3-(silyloxy)alk-2-en-1-ones.     

Novel catalytic hydrogenolysis of silyl enol ethers by the use of acidic ruthenium dihydrogen complexes

Treatment of 1-trimethylsilyloxy-1-cyclohexene (1a) in the presence of a catalytic amount of the acidic dihydrogen complex [RuCl(η²-H₂)(dppe)₂]OTf (4a) [dppe=1,2-bis(diphenylphosphino)ethane, OTf=OSO₂CF₃] (10 mol.%) under 1 atm of H₂ in anhydrous ClCD₂CD₂Cl at 50 °C for 8 h afforded cyclohexanone (3a) and Me₃SiH in quantitative NMR yields. Silyl enol ethers such as 1-triethylsilyloxy-1-cyclohexene (1b), 1-t-butyldimethylsilyloxy-1-cyclohexene (1c), and other trimethylsilylethers (1d, 1e, and 1f) reacted similarly with H₂ to afford the corresponding ketones and trialkylsilanes. The direct proton transfer from H₂ to the trimethylsilyl enol ethers (1a and 1d-1f) was confirmed by the experiments employing D₂ gas, where α-monodeuterated ketones (3a′ and 3d′-3f′) were obtained in high yields. The enantioselective protonation of prochiral silyl enol ethers with 1 atm of H₂ by employing [RuCl(η²-H₂)((S)-BINAP)₂]OTf (4e) [BINAP=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl] and [RuCl(η²-H₂)((R, R)-CHIRAPHOS)₂]OTf (4f) [CHIRAPHOS=2,3-bis(diphenylphosphino)butane] showed that no enantioselectivity was observed in either catalytic or stoichiometric protonation reactions under various reaction conditions. The reaction of [RuHCl(dppe)₂] (5a) with one equivalent of Me₃SiOTf under 1 atm of H₂ produced rapidly 4a, concurrent with the formation of Me₃SiH. Based on these studies, the mechanism for this novel hydrogenolysis of silyl enol ethers is proposed which involves heterolytic cleavage of the coordinated H₂ on the ruthenium atom caused by the nucleophilic attack of the oxygen atom of enol ethers to give ketones and Me₃SiOTf, and the subsequent reaction of the resultant complex 5a with Me₃SiOTf under 1 atm of H₂ to regenerate the original dihydrogen complex 4a. On the other hand, the stoichiometric reaction of a lithium enolate 6e with one equivalent of 4e at −78 °C in CH₂Cl₂ under 1 atm of H₂ afforded 2-methyl-1-tetralone (3e) with 75% ee (S) in >95% yield, together with the formation of [RuHCl((S)-BINAP)₂] (5e).     

Catalytic olefination reaction of carbonyl compounds. A study on stereoselectivity of alkene formation

The mechanism of formation of alkene stereoisomers in the catalytic olefination reaction of carbonyl compounds was studied. 4-Chlorobenzaldehyde hydrazone 1 stereoselectively reacts with a number of F-, Cl-, Br-, and I-containing polyhaloalkanes in the presence of catalytic amounts of CuCl to give -substituted styrenes 2 with the more thermodynamically stable alkene isomer being the major product. A model for the formation of the stereoisomers of alkenes 2 in the olefination reaction is proposed. Stereoselectivity of the reaction is determined by elimination of copper(ii) halides from the lowest-lying conformers of organocopper intermediates II. According to quantum-chemical calculations, the elimination should involve the staggered conformations with antiperiplanar arrangement of C—Hal and C—Cu bonds and proceed by the E2 anti-elimination mechanism. The results of quantum-chemical calculations are in good agreement with the experimental E/Z alkene isomer ratios.     

Regioselective synthesis of bis(silyl enol ethers) and bis(conjugated enones) through electron transfer from Mg metal

Treatment of α,β-unsaturated ketones with Mg metal in the presence of trimethylsilyl choride (TMSCl) brought about facile and regioselective reductive dimerization to give the corresponding bis(silyl enol ethers), 1,6-bis(trimethylsilyloxy)-1,5-dienes. Similar Mg-promoted reductive dimerization of 1,3-cyclic diketones in the presence of TMSCl followed by acid-catalyzed hydrolysis led to selective formation of the corresponding 1,6-diketo-2,4-dienes in moderate to good yields.     

Synthesis of 3,5-dioxoalkanoates, 3,5-dioxopimelates and 2,4-dioxoadipates by acylation of 1,3-bis-silyl enol ethers

3,5-Dioxoalkanoates, 3,5-dioxopimelates and 2,4-dioxoadipates were prepared by acylation of 1,3-bis-silyl enol ethers with carboxylic chlorides, methyl 3-chloro-3-oxopropanoate and ethyl 2-chloro-2-oxoacetate, respectively.     

One-pot synthesis of aryl fluorides by [3+3] cyclization of 1,3-bis(silyl enol ethers) with 2-fluoro-3-silyloxy-2-en-1-ones

Functionalized aryl fluorides were regioselectively prepared by [3+3] cyclization of 1,3-bis(silyl enol ethers) with 2-fluoro-3-silyloxy-2-en-1-ones.