Unexpected Hydrobromic Acid-Catalyzed CC Bond-Forming Reactions and Facile Synthesis of Coumarins and Benzofurans Based on Ketene Dithioacetals

A [5 + 1] annulation strategy for the synthesis of multifunctional biaryls and p-teraryls from 1,6-Michael acceptor ketene dithioacetals

A [5 + 1] annulation approach was used to access multifunctional biaryls and p-teraryls from ketene dithioacetals.

Addition of dithi(ol)anylium tetrafluoroborates to α,β-unsaturated ketones

In the presented study, dithi(ol)anylium tetrafluoroborates are added to α,β-unsaturated ketones in a Michael-type reaction yielding diverse substituted ketene diothi(ol)anes. The reactions proceed at room temperature in 1 or 13 h without the need of further additives. The presented procedure is in particular useful for dithi(ol)anylium tetrafluoroborates without electron-withdrawing groups in α-position. This is advantageous with respect to previous approaches, which were limited to the use of ketene dithioacetals substituted with electron-withdrawing groups. Aiming for the systematic investigation of possible steric and electronic influences on the outcome of the reaction, various combinations of electrophiles and nucleophiles were used and the results of the reactions were compared based on the type of the used dithioacetal. The scope of the presented procedure is shown with four additional transformations including the use of additional electrophiles and nucleophiles, the use of a chiral auxiliary and subsequent reduction of selected products. Additionally, we extended the reaction to the synthesis of diene dithiolanes by addition of an ynone to α-alkyl or aryl-substitued dithiolanylium TFBs.

Mechanistic investigation inspired "on water" reaction for hydrobromic acid-catalyzed Friedel-Crafts-type reaction of β-naphthol and formaldehyde

The mechanism of the HBr-catalyzed Friedel-Crafts-type reaction between β-naphthol and HCHO was investigated by DFT to improve this reaction. The HBr-H₂ O co-catalyzed the preferential pathway undergoes the concerted nucleophilic addition and hydrogen shift, stepwise followed by H₂ O elimination and the CC bond formation. The origin of the high catalytic activity of HBr is ascribed to CH···Br^- and OH···Br^- interactions, which suggest that the active species is Br^- . Moreover, water molecules efficiently assist in improving the activity of Br^- . The computational results show that solvent polarity profoundly affects the activation barriers. To our delight, the activation barrier of the rate-determining step for the favored pathway in water is comparable (0.6 kcal/mol difference) with that in acetonitrile. The experimental observation further confirmed our results and demonstrated that the title reaction can be successfully achieved "on water." Therefore, we open a new efficient and green strategy for the synthesis of biphenol derivatives. © 2017 Wiley Periodicals, Inc.

Br2- or HBr-catalyzed synthesis of asymmetric 3,3-di(indolyl)indolin-2-ones

Under the catalysis of 1 mol% of Br

Direct thiocyanation of ketene dithioacetals under transition-metal-free conditions

The first direct thiocyanation of ketene dithioacetals has been accomplished in the presence of N-chlorosuccinimide (NCS) and NH₄SCN under transition-metal-free conditions. Terminal alkenes and hydrazine were identified to be qualified candidates for the process as well.

Br2-Catalyzed regioselective dehydrative coupling of indoles with acyloins: direct synthesis of α-(3-indolyl) ketones

An efficient Br₂-catalyzed synthesis of α-(3-indolyl) ketones via dehydrative coupling of simple indoles with acyloins is presented.

Synergistic catalysis-induced ring-opening reactions of 2-substituted 3,4-dihydropyrans with α-oxoketene dithioacetals

Synergistic catalysis enables ring-opening reactions of 2-substituted 3,4-dihydropyrans with α-oxoketene dithioacetals to proceed very well.

Radical 5-exo cyclization of alkynoates with 2-oxoacetic acids for synthesis of 3-acylcoumarins

A silver-promoted decarboxylative annulation of alkynoates with 2-oxoacetic acids leading to the formation of 3-acyl-4-arylcoumarins is reported. The process involves radical decarboxylative acylation, 5-exo cyclization, and ester migration.

Iron-catalyzed alkylation of α-oxo ketene dithioacetals

Iron-catalyzed alkylation of α-oxo ketene dithioacetals by styrenes efficiently afforded highly functionalized tetrasubstituted olefins.

Recent developments of ketene dithioacetal chemistry

Ketene dithioacetals are versatile intermediates in organic synthesis. Extensive research, since the last decade, has given rise to new prospects in their chemistry. The objective of this review is twofold: first, to highlight the new prospects in the chemistry of functionalized ketene dithioacetals, and second, to provide an intrinsic link between ketene dithioacetal groups and a variety of other functional groups, which has brought out many new facts that will assist in future designs.