The α-acetyl ketene dithioacetals 2, which bear various alkylthio groups, are a kind of important intermediates in organic synthesis. In this paper, dithioacetals 2 were prepared in very high yields (90%—100%) via t...The α-acetyl ketene dithioacetals 2, which bear various alkylthio groups, are a kind of important intermediates in organic synthesis. In this paper, dithioacetals 2 were prepared in very high yields (90%—100%) via the deacetylation reaction of the corresponding α,α-diacetyl ketene dithioacetals 1 in the presence of concentrated sulfuric acid. This reaction involves an %in-situ% electrophilic addition-deacetylation mechanism and shows the nucleophilicity of the α-carbon atom in α-oxo ketenedithioacetals. Meanwhile, when the reaction time was prolonged to 22—25 h, the β-keto thiolesters 3a and 3c were produced in good yields.展开更多
As a kind of versatile synthons, α-oxoketene dithioacetals have found their wide utilizations in organic synthesis. Owing to the interaction between two electron donating groups(RS) and an electron withdrawing group ...As a kind of versatile synthons, α-oxoketene dithioacetals have found their wide utilizations in organic synthesis. Owing to the interaction between two electron donating groups(RS) and an electron withdrawing group in the α position, the α-carbon atom of α-EWG ketene S,S-acetals shows a high nucleophilicity. In this paper, the reactions of α-acetyl cyclic ketendithioacetals with a series of acyl chlorides were performed and a new route to the C～C bond formation reaction at the α-carbon atom of α-oxoketene dithioacetals was described. By the above reactions, α-acetyl-α-acyl ketendithioacetals were prepared with good to high yields(55%～82%) via the acylation of α-acetyl cyclic ketendithioacetals at the α-carbon atom of α-acetyl ketendithioacetals mediated by titanium tetrachloride in dry dichloromethane at reflux temperature. The mechanism of the acylation between compound 1 and acyl chloride was proposed, which belongs to nucleophilic addition-elimination reaction.展开更多
The behavior of α,α-diacetyl ketene dibenzylthioacetal 1a under basic conditions was studied. Catalyzed by steric hindered base as t-BuONa(in t-BuOH), α-acetyl ketene dibenzylthioacetal 2a could be obtained in 98% ...The behavior of α,α-diacetyl ketene dibenzylthioacetal 1a under basic conditions was studied. Catalyzed by steric hindered base as t-BuONa(in t-BuOH), α-acetyl ketene dibenzylthioacetal 2a could be obtained in 98% yield within 3 min via deacylation of 1a. Assisted by t-BuONa(in t-BuOH), α-cinnamoyl ketene dibenzylthioacetals were produced in high yields by reacting both 1a and 2a with arylaldehydes; whereas, under the same conditions, the corresponding α,α-dicinnamoyl ketene dibenzylthioacetals 4 were formed when furan-2-carbaldehyde and thiophene-2-carbaldehyde were used as the electrophiles. These evidences support the proposed mechanism that, catalyzed by t-BuONa (in t-BuOH), the reaction of 1a with arylaldehydes may normally proceed via a sequential deacylation-condensation process and the formation of double condensation products 4 may be due to the higher activity of furan-2-carbaldehyde and thiophene-2-carbaldehyde under the selected reaction conditions.展开更多
α,α-diacetyl ketene thioacetals had been investigated as odorless thiol equivalents in thia-Michael addition reaction.Under solvent-free conditions,a series of reactions between α,α-diacetyl ketene thioacetals and...α,α-diacetyl ketene thioacetals had been investigated as odorless thiol equivalents in thia-Michael addition reaction.Under solvent-free conditions,a series of reactions between α,α-diacetyl ketene thioacetals and α,β-unsaturated ketones were carried out promoting by concentrated hydrochloric acid.The corresponding thia-Michael adducts in high yields were obtained.Furthermore,a mechanism for this thia-Michael addition reaction was proposed preliminary.展开更多
Bromo ketene dithioacetals (5) were prepared in high yields by reaction of α,α-diacetyl ketene dithioacetals (4) with bromine catalyzed by FeBr 3 at room temperature. This new reaction is proposed involving an ipso ...Bromo ketene dithioacetals (5) were prepared in high yields by reaction of α,α-diacetyl ketene dithioacetals (4) with bromine catalyzed by FeBr 3 at room temperature. This new reaction is proposed involving an ipso electrophilic addition-deacetylation mechanism.展开更多
文摘The α-acetyl ketene dithioacetals 2, which bear various alkylthio groups, are a kind of important intermediates in organic synthesis. In this paper, dithioacetals 2 were prepared in very high yields (90%—100%) via the deacetylation reaction of the corresponding α,α-diacetyl ketene dithioacetals 1 in the presence of concentrated sulfuric acid. This reaction involves an %in-situ% electrophilic addition-deacetylation mechanism and shows the nucleophilicity of the α-carbon atom in α-oxo ketenedithioacetals. Meanwhile, when the reaction time was prolonged to 22—25 h, the β-keto thiolesters 3a and 3c were produced in good yields.
文摘As a kind of versatile synthons, α-oxoketene dithioacetals have found their wide utilizations in organic synthesis. Owing to the interaction between two electron donating groups(RS) and an electron withdrawing group in the α position, the α-carbon atom of α-EWG ketene S,S-acetals shows a high nucleophilicity. In this paper, the reactions of α-acetyl cyclic ketendithioacetals with a series of acyl chlorides were performed and a new route to the C～C bond formation reaction at the α-carbon atom of α-oxoketene dithioacetals was described. By the above reactions, α-acetyl-α-acyl ketendithioacetals were prepared with good to high yields(55%～82%) via the acylation of α-acetyl cyclic ketendithioacetals at the α-carbon atom of α-acetyl ketendithioacetals mediated by titanium tetrachloride in dry dichloromethane at reflux temperature. The mechanism of the acylation between compound 1 and acyl chloride was proposed, which belongs to nucleophilic addition-elimination reaction.
文摘The behavior of α,α-diacetyl ketene dibenzylthioacetal 1a under basic conditions was studied. Catalyzed by steric hindered base as t-BuONa(in t-BuOH), α-acetyl ketene dibenzylthioacetal 2a could be obtained in 98% yield within 3 min via deacylation of 1a. Assisted by t-BuONa(in t-BuOH), α-cinnamoyl ketene dibenzylthioacetals were produced in high yields by reacting both 1a and 2a with arylaldehydes; whereas, under the same conditions, the corresponding α,α-dicinnamoyl ketene dibenzylthioacetals 4 were formed when furan-2-carbaldehyde and thiophene-2-carbaldehyde were used as the electrophiles. These evidences support the proposed mechanism that, catalyzed by t-BuONa (in t-BuOH), the reaction of 1a with arylaldehydes may normally proceed via a sequential deacylation-condensation process and the formation of double condensation products 4 may be due to the higher activity of furan-2-carbaldehyde and thiophene-2-carbaldehyde under the selected reaction conditions.
文摘α,α-diacetyl ketene thioacetals had been investigated as odorless thiol equivalents in thia-Michael addition reaction.Under solvent-free conditions,a series of reactions between α,α-diacetyl ketene thioacetals and α,β-unsaturated ketones were carried out promoting by concentrated hydrochloric acid.The corresponding thia-Michael adducts in high yields were obtained.Furthermore,a mechanism for this thia-Michael addition reaction was proposed preliminary.
文摘Bromo ketene dithioacetals (5) were prepared in high yields by reaction of α,α-diacetyl ketene dithioacetals (4) with bromine catalyzed by FeBr 3 at room temperature. This new reaction is proposed involving an ipso electrophilic addition-deacetylation mechanism.
