Superelectrophilic Activation of Crotonic/Methacrylic Acids: Direct Access to Thiochroman-4-ones from Benzenethiols by Microwave-Assisted One-Pot Alkylation/Cyclic Acylation.

An efficient microwave-assisted protocol for the synthesis of 2-/3-methylthiochroman-4-ones by superacid-catalyzed alkylation followed by cyclic acylation (cyclization via intramolecular acylation) is described. Using easily accessible benzenethiols and crotonic acid/methacrylic acid with triflic acid (as catalyst of choice for needed optimal acidity), the reaction was tuned toward the formation of the cyclized products in good selectivity and yield. A mechanism involving the formation of carbenium-carboxonium superelectrophilic species is suggested.

Preparation of trifluoromethylated dihydrocoumarins, indanones, and arylpropanoic acids by tandem superacidic activation of 2-(trifluoromethyl)acrylic acid with arenes.

Indanones and coumarins are important intermediates for the convenient synthesis of many pharmaceutical and biologically active compounds. Fluoroorganics play a vital role in the design of very effective therapeutics due to significant enhancenment in their lipophilicity, bioavailability, and fast uptake by the presence of fluorine in these molecules. Herein, we report an efficient one-pot synthesis of trifluoromethylated arylpropanoic acids, indanones, and dihydrocoumarins using Friedel-Crafts alkylation or tandem Friedel-Crafts alkylation-cycloacylation of arenes/phenols with 2-(trifluoromethyl)acrylic acid under superacidic conditions using trifluoromethanesulfonic acid. The results have been rationalized by the structure energy calculations of the involved reaction intermediates using ab initio theoretical methods.

Efficient nucleophilic fluoromethylation and subsequent transformation of alkyl and benzyl halides using fluorobis(phenylsulfonyl)methane.

An efficient methodology for the nucleophilic fluoromethylation of alkyl and benzyl halides using alpha-fluoro-alpha-(phenylsulfonyl)methane (1) as a highly versatile reagent is reported. Using benzyl halides, stereospecific one-pot synthesis of alpha-fluorovinyl compounds such as alpha-fluorostyrylsulfones, alpha-fluorocinnamates, and alpha-fluorochalcones has been achieved. The methodology has been extended toward the synthesis of alpha-substituted fluoroalkane derivatives using selective reductive desulfonylation conditions.

Gallium (III) triflate-catalyzed synthesis of heterocycles: quinoxalines, 1,5-benzodiazepines and their fluorinated derivatives.

BACKGROUND: The quinoxaline nucleus is a part of several antibiotics, such as echinomycin, levomycin and actinomycin, which are known to inhibit the growth of Gram-positive bacteria and are active against various transplantable tumors. Benzodiazepines are important classes of heterocycles that draw significant interest from the pharmaceutical industry because of their prominent therapeutic value, such as antiviral, antibacterial, anti-inflammatory, antiprotozoaval properties and also as kinase inhibitors. They have also been evaluated as anticancer, anthelmintic, antifungal and insecticidal agents. RESULTS & CONCLUSION: Quinoxalines, benzodiazepines and their fluorinated derivatives have been prepared in excellent yields from the corresponding diamines and diketones using gallium (III) triflate as an efficient and environmentally friendly catalyst, due to its stability, recyclability and minimal toxicity.

Efficient 1,4-addition of alpha-substituted fluoro(phenylsulfonyl)methane derivatives to alpha,beta-unsaturated compounds.

The 1,4-addition of a monofluoromethyl nucleophile to a variety of alpha,beta-unsaturated compounds has been achieved under mild conditions using either phosphines or potassium carbonate at room temperature. alpha-Substituted fluoro(phenylsulfonyl)methane easily undergoes Michael addition to alpha,beta-unsaturated ketones, esters, nitriles, sulfones, as well as propynoates at room temperature to yield the corresponding adducts in moderate to excellent yields.

Gallium (III) triflate catalyzed efficient Strecker reaction of ketones and their fluorinated analogs.

The synthesis of alpha-aminonitriles and their fluorinated analogs has been carried out in high yield and purity by the Strecker reaction from the corresponding ketones and amines with trimethylsilyl cyanide using gallium triflate in dichloromethane. Monofluoro-, difluro-, or trifluoromethyl groups can be incorporated into the alpha-aminonitrile product by varying the nature of the fluorinated ketones. Study with various fluorinated and nonfluorinated ketones reveals that the choice of proper catalyst and the solvent system (suitable metal triflates as a catalyst and dichloromethane as a solvent) plays the key role in the direct Strecker reactions of ketones.

Effect of carbonates/phosphates as nucleophilic catalysts in dimethylformamide for efficient cyanosilylation of aldehydes and ketones.

Cyanosilylation of aldehydes and aliphatic ketones can be carried out in dimethylformamide even without the use of any catalyst. In the presence of nucleophilic catalysts such as carbonate and phosphate salts, the reaction rate is significantly enhanced.

Efficient one-pot synthesis of fluorinated benzimidazolines, benzothiazolines, benzoxazolines, and dihydrobenzoxazinones using gallium(III) triflate as a catalyst.

One-pot synthesis of fluorinated benzimidazolines, benzothiazolines, benzoxazolines, and dihydrobenzoxazinones was easily achieved under mild conditions in high yields and purity through gallium(III) triflate mediated condensation-cyclization. Introduction of fluorine atoms favors the formation of the five-membered heterocycles over seven-membered heterocycles. [reaction: see text].

Facile synthesis of TMS-protected trifluoromethylated alcohols using trifluoromethyltrimethylsilane (TMSCF3) and various nucleophilic catalysts in DMF.

Organofluorine compounds are becoming increasingly important in different fields, such as material science, agro chemistry, and the pharmaceutical industry. Nucleophilic trifluoromethylation is one of the widely used methods to incorporate a trifluoromethyl moiety into organic molecules. We have carried out extensive studies to develop varieties of easily accessible nucleophilic catalysts to promote such reactions. TMS-protected trifluoromethylated alcohols were prepared from both aldehydes and ketones in excellent yields using catalytic amount of amine N-oxide. Carbonate and phosphate salts also showed efficient catalytic activity toward this reaction. These reactions were highly solvent dependent, and DMF was found to be the most suitable one among the various solvents studied. All these reactions proceeded under very mild conditions, giving clean products and avoiding the use of any fluoride initiators or expensive catalysts, and extremely water-free conditions. The mechanism for the reaction is discussed in detail. DFT calculations were performed on the possible reaction intermediates using the Gaussian 03 program at B3LYP/6-311+G* level to support the proposed mechanism.