Palladium(0)-Catalyzed, Copper(I)-Mediated Coupling of Boronic Acids with Cyclic Thioamides. Selective Carbon−Carbon Bond Formation for the Functionalization of Heterocycles^†

Abstract

The palladium-catalyzed cross-coupling of cyclic thioamides with arylboronic acids in the presence of stoichiometric amounts of a copper(I) cofactor is described. The desulfitative carbon-carbon cross-coupling protocol is performed under neutral conditions and can be applied to a range of heterocyclic structures with embedded thioamide fragments. Successful carbon-carbon cross-coupling is independent of the ring size, aromaticity/nonaromaticity, the presence of additional heteroatoms, or other functional groups in the starting thioamide structure. Employing controlled microwave irradiation at 100 degrees C, most cross-couplings can be completed within 2 h and proceed in high yields. An advantage of using thioamides as starting materials is the fact that the system can be tuned to an alternative carbon-sulfur cross-coupling pathway by changing to stoichiometric copper(II) under oxidative conditions. Both types of thioamide cross-couplings are orthogonal to the traditional base-catalyzed Suzuki-Miyaura cross-coupling of aryl halides with boronic acids.

Synthesis of diverse dihydropyrimidine-related scaffolds by fluorous benzaldehyde-based Biginelli reaction and post-condensation modifications

“…Dihydropyrimidinethione 4f was used for the Liebeskind–Srogl coupling reaction with a phenylboronic acid to convert to 2-aryl-1,6-dihydropyrimidine 9 [18–20]. The reaction was performed following a literature procedure [21] and was catalyzed by Pd(PPh 3 ) 4 and copper(I) thiophene-2-carboxylate (CuTC) under microwave heating at 100 °C for 25 min to afford aryl-substituted dihydropyrimidine 9 in 76% yield.…”

New transformation of α-acetylenic ketones under the action of 1,2-diaminoethane

“…NMR spectra were recorded on a Bruker AV 400 spectrometer (400.13 MHz) in CDCl 3 or DMSO d 6 . Mass spectra were obtained on a Thermo Scientific DFS instrument (Double Focusing Sector Mass Spectrometer, Thermo Electron Corporation) with the direct inlet of the sample (the temper ature of the ionization chamber was 220-270 °C, the ionization potential was 70 eV).…”

Recent Developments in Microwave‐Assisted, Transition‐Metal‐Catalysed C–C and C–N Bond‐Forming Reactions

“…[99] According to the authors, the reaction is independent of ring size, aromaticity/nonaromaticity and the presence of additional heteroatoms or other functional groups in the starting thioamide. [100] Interestingly, it was demonstrated that although the catalytic Pd 0 /Cu I system resulted solely in carbon-carbon bond formation, the use of stoichiometric amounts of Cu II under an air atmosphere resulted in carbon-sulfur bond formation (Scheme 76). [98,99] It has been shown that both types of thioamide cross-couplings are orthogonal to the traditional base-catalysed Suzuki-Miyaura cross-coupling of aryl halides with boronic acids.…”