Chemoselective Bromodecarboxylation ofα-Carboxy-α-cinnamoyl Ketene Cyclic Dithioacetals

α-Oxoketene dithioacetals（ compound 1 ） are versatile synthons for organic synthesis due to their specially structural characteristic, that is, the masked ketene is conjugated with the convertible carbonyl in their molecules. Although there have been numerous reports covering the reactions in which they have been taken as 1,3-electrophiles, the reaction at the α-carbon atom of α-oxoketene dithioacetals has seldom been investigated. Junjappa and co-workers found the α- bromination of compound 2 in the presence of NBS led to α-aroyl-α-bromo ketenedithioacetals. However, the flexibility of the functional groups at the α-carbon atom of compound 2 are still limited.

Synthesis of 2-Alkyl(aryl)-3-methylthio-6-methyl-6-arylpyrano-[4, 3-c] pyrazol-4(2H)-ones

The synthesis of 2-alkyl(aryl)-3-methylthiopyrano[4,3-c]pyrazol-4(2H)-ones via 5, 6- dihydro-2H-pyran-2, 4-dione-3-dithioacetals with (un)substituted hydrazines is described and the mechanism of the formation of title compounds is discussed. Their structures were confirmed by 1HNMR spectra and elemental analysis.

Condensation Reaction of α-Aroyl-α-acetyl Ketene Cyclic Dithioacetals with Aromatic Aldehydes

The title compounds 3 and 4 condensed with aromatic aldehydes to give a--aroylsicinnamoyl ketene cyclic dithioacetals 5 and 6 with sodium ethoxide as the base. The stereochemistryofs and 6 was assigned as E-configuration by 1H NMR.

STUDIES ON THE REACTIVITY OF CYCLOAROMATIZATION REACTION VIA a－OXO KETENE DITHIOACETALS

The dihydric dithioketenes 3a-c obtained by 1,2-addition of methallyl Grignard reagent to bis(alkylthio)methylidene derivative ofdimedone 2a-c wewr converted to the cycloaromatization product 4 assisted by boron trifluoride etherate.When this reaction was performed in methanol,the substitution-cycloaroatization product 5 was obtained as by- product from 3c.To this eycloaromatization reaction,,the reactivity order dimethylthio>1, 3 - propylenedithio>1, 2- ethylenedithio carbon cation was established by the yields from 3a-c 4.An intramolecular a1,a1reaction pattern was developed by experiment.

SYNTHESIS OF 1, 1-DIALKYLTHIO—1, 3, 5—HEXATRIENES WITH α—OXOKETENE DITHIOACETALS

α-Oxoketene dithioacetals 2 via, 1,2-nucleophilic addition by allyl magnesium bromide afforded corresponding alcohols (3).Treated with water and catalyzed by Lewis acid, the alcohols 3 were converted regiospecifically to the conjugated 1,1—dialkylthio—1,3,5 hexatrienes (4). Both the alcohol 8 and its methoxy methyl ether 9 were sensative to dilute sulfuric acid and cyclized under this condition to form the aryl methylthio ether (10).

Stepwise Oxidation of Ketene Dithioacetal

Stepwise oxidation of ketene dithioacetal is found and the different oxidation products changed with the amount of oxidant, temperature and reaction time.

α-OXOKETENE CYCLIC DITHIOACETAL CHEMISTRY(XⅢ)-THE ETHERIFYING REACTION ON THE ADDUCTS OF ALIPHATIC α-OXO KETENE CYCLIC DITHIOACETALS WITH ALLYL MAGNESIUM BROMIDE

Aliphatic α-oxo ketene cyclic dithioacetals 1 were reacted with allyl magne- sium bromide to afford the 1,2-addition products 2.Catalyzed by boron trifluoride etherate,the adducts 2 were etherified by methanol to afford the corresponding methyl ethers 3.This process provides a new method for the protection of the acid sensitive hydroxyl group in 2 under mild condition.

A Convenient Synthesis of Pyrazolylpyrazoles Using α-Oxo Ketene S,S- and N,S-Acetals

Substituted pyrazolylpyrazoles were synthesized through the reaction of hydrazine hydrate and α-oxo-(3, 5-dimethyl-1 H-pyrazole-1-ly)ketene S, S- and N,S-Acetals which were obtained from α-oxo-(3,5-dimethyl-1 H-pyrazole-1-yl) acetophenone. Pyrazolylpyrazole was also prepared via α-oxo ketene N,O-acetal by way of ring chain transformation.

Synthesis, Spectroscopic Characterization and Antimicrobial Activity of Some New 2-Substituted Imidazole Derivatives

The reaction of imidazole-2-thione derivative 1 with 2-chloro-N-p-tolylacetamide afforded the corresponding 2-(1HI-imidazol-2-ylthio)-N-p-tolylacetamide 2. Reaction compound 2 with different reagents such as p-chlorobenzaldehyde and p-chlorophenyl diazonium chloride afforded the corresponding arylidene derivative 3 and hydrazone derivative 6. Reactions of 2 with carbon disulfide in dimethylformamide (DMF) in one equivalent potassium hydroxide afforded intermediate potassium sulphide salt 8, which treatment with dilute hydrochloric acid and phenacyl bromide afforded the corresponding 2-[p-tolylcarbamoyl]ethanedithioic acid 9 and 3-[benzo-ylmethylthio]-N-p-tolyl-3-thioxo-propaneamide 10. While the reaction 2 with carbon disulphide in the presence of two equivalent potassium hydroxide in DMF gave non-isolated potassium salt 11, which was allowed to react with halogenated compounds namely ethyl chloroacetate and methyl iodide afforded the corresponding 3, 3-bis[(ethoxycarbonyl)methylthio]-N-p-tolylacrylamide 12 and 3,3-bis-(methylthio)-N-p-tolylacrylamide 13 respectively. Reaction 2 with phenyl isothiocyanate in basic DMF yielded the intermediate potassium sulphide salt 18. Acidification 18 with dilute hydro-chloric acid afforded the corresponding thiocarbamoyl derivative 19. Treatment of intermediate 18 with methyl iodide, phenacyl bromide and ethylchloroacetate afforded the 3-anilino-3-(methylthio)-N-p-tolylacrylamide 20, 2-(1,3-thiazol-2(3H)-ylidene)-N-p-tolylacetamide 21 and 2-(4-oxo-3-phenyl-1,3-thiazolidin-2-ylidene)-N-p-tolylacetamide 22 respectively. The structure of the newly synthesized compounds has been confirmed by elemental analysis and spectra data. Synthesized compounds 2, 3, 6, 13, 15a, 15b, 17, 20, 21, 22 and 23 were screened for their antibacterial activities in vitro against Gram-positive (Staphylococcus aureus and Bacillus subtilis), Gram-negative (Pseudomonas aeuroginosa and Escherichia coli ) and antifungal activities against (Aspergillus fumigates, Syncephalastrum racemosum, Geotrichum candidum and Candida albicans).

Synthesis of Triphenyltin 2-(1,2-Ethylenedithio) Methylene-3-Oxo-5-Aryl-4-Pentenoate

Under esterification conditions, 2-(1,2-ethylenedithio) methylene-3-oxo-5-aryl-4-pentenoic acid 3 afforded the decarboxylated products 4. The triphenyltin 2-(1, 2-ethylenedithio) methylene-3-oxo-5-aryl-4-pentenoates 5 were obtained in high yields when 3 reacted with triphenyltin hydroxide.

An Efficient and Odorless Synthesis of Thioethers Using 2-[Bis（alkylthio）methylene]-3-oxo-N-o-tolylbutanamides as Thiol Equivalents

Using 2-[bis（alkylthio）methylene]-3-oxo-N-o-tolylbutanamides 1 as odorless thiol equivalents, an efficient and odorless synthesis of thioethers has been developed. Promoted by NaOH in EtOH, the cleavage of 1 commences to generate thiolate anions, and the generated thiolate anions then react with halides to give various thioethers in good yield. It is noteworthy that only a very faint odor ofthiols can be perceived during both the reaction and the workup.

Iron Chloride Hexahydrate-catalyzed Friedel-Crafts Akylation of Cyclic Ketene Dithioacetals with Alcohols

A cost-effective and environmentally compliance FeCl3·6H2O catalyzed Friedel-Crafts alkylation of cyclic ketene dithioacetals with alcohols was developed. The reaction was efficient in the presence of catalyst loading as low as 5%（molar fraction） in CH2Cl2 solvent at room temperature or under reflux conditions. A wide range of alkylated ketene dithioacetals were synthesized in excellent yields.

FeCl3-6H2O-Catalyzed Synthesis of β-Ketothioesters from Chain α-Oxo Ketene Dithioactals

A FeCl3-6H2O-catalyzed synthesis of β-ketothioesters from the hydrolysis reaction of chain α-oxoketene dithioacetals was carried out. Subsequently, we explored the FeCl3-6H2O-catalyzed Friedel-Crafts alkylation of the synthesized fl-ketothioesters with alcohols in CH3CN at 25 ℃, affording the desired α-alkylated fl-ketothioesters in excellent yields. Wide scope of the substrates, use of inexpensive reagents, high yields under mild reaction conditions are notable features of these reactions.

Azo-coupling Decarboxylation Reaction of α-Carboxy Ketene Dithioacetals in Water-a New Route to 1,2-Diaza-1,3-butadienes

Under basic conditions, a series of 4,4-dialkylthio-l,2-diaza-l,3-butadienes were synthesized in good to excellent yields via a novel azo-coupling decarboxylation reaction by reacting a-carboxyl ketene dithioacetals with aryldiazonium salts in aqueous medium.

Polarized Ketene Dithioacetals-Versatile Synthons for Different Heterocycles

The reactivity of polarized ketene dithioacetals to develop a variety of heterocycles under different conditions was studied.

Dynamic Ring-chain Equilibrium of Nucleophilic Thiol-yne "Click" Polyaddition for Recyclable Poly(dithioacetal)s

We report a dynamic polymerization system based on the reversible nucleophilic Michael polyaddition of activated alkynes and dithiols.Four poly(dithioacetal)s(P1-P4)were prepared via the base-catalyzed thiol-yne"click"polyaddition of two dithiols(1,4-butanedithiol(4S)and 1,5-pentanedithiol(5S))and two alkynones(3-butyn-2-one(Y1)and 1-phenyl-2-propyn-1-one(Y2))at high concentrations.We systematically investigated the base-catalyzed polymerization of 4S and Y1(for polymer PI)under different conditions,and found that this polymerization was a highly concentration-dependent dynamic system:polymer PI was formed at high concentration,while seven-membered dithioacetal,1-(1,3-dithiepan-2-yl)propan-2-one(C1),was obtained at low concentration.The polymerization of 4S and Y2(for polymer P4)displayed similar polymerization behavior,generating 2-(1,3-dithiepan-2-yl)-1-phenylethanone(C4)at low concentration.On the contrary,polymer P2(from Y1 and 5S)was exclusively obtained with no formation of eight-membered dithioacetal.The polymerizations of Y1 with 1,2-ethanedithiol(2S)and 1,3-dimercaptopropane(3S)only afforded corresponding five-and six-membered dithioacetals,1-(1,3-dithiolan-2-yl)propan-2-one(C2)and 1-(1,3-dithian-2-yl)propan-2-one(C3).This dynamic behavior of PI and P4 was attributed to the concentration-dependent retro-Michael addition reaction between a thiol and a β-sulfido-α,β-unsaturated carbonyl compound catalyzed by bases.Furthermore,polymers P1 and P4 could be depolymerized into Cl and C4 in yields of 58% and 95%,respectively.The ring-opening polymerization of Cl at high concentration could successfully regenerate polymer PI.Thus,a new type of closed-loop recyclable poly(dithioacetal)s was developed.

Controllable cross-coupling of thiophenols with dichloromethane mediated by consecutively paired electrolysis

Chloroalkanes are important building blocks in the synthesis,but their use in redox chemistry is limited by their negative reduction potentials.Electrosynthesis can precisely control the reaction energy just by adjusting the current or voltage to achieve the selectivity of regulation.In this study,the consecutively paired electrolyticmediated controllable radical cross-coupling of thiophenols with dichloromethane was developed to deliver the dithioacetals,sulfides,and sulfoxides in the absence of electrochemical mediator conditions.It features broad substrate scope,simple operation,gram-scale synthesis,and is eco-friendly.Mechanistic studies reveal that this electrochemical reaction is radical-induced cross-coupling of thiophenols with dichloromethane.

A novel approach towards dethioacetalization reactions with H_2O_2-SOC1_2 system

A simple and efficient protocol for the deprotection of dithioacetal,1,3-dithianes and 1,3-dithiolanes has been developed using H_2O_2-SOC1_2 reagent system.In addition to the absence of overoxidation products for oxidation-prone substrates,high chemoselectivity, the low cost and availability of the reagents,simplicity of the method,short reaction times,and excellent yields can also be considered as strong points for this method.

Synthesis of 2-Benzylthio-5-phenyl-3,4-disubstituted Thiophenes by Intramolecular Condensation of α-Oxo Ketene Dibenzyl^thioacetals

A facile route to 2-benzylthio-5-phenyl-3,4-disubstituted thiophenes was described. Catalyzed by sodium hydroxide, the title compounds were synthesized in moderate to good yields simply from the intramolecular aldol type condensation of α-oxo ketene dibenzylthioacetals. The chemical selectivity for this annulation reaction was studied and discussed.