Ligand-free Pd/Ag-mediated dehydrogenative alkynylation of imidazole derivatives

Abstract

The regioselective synthesis of 2-alkynyl(benz)imidazoles was successfully achieved by Pd(ii)/Ag(i)-mediated dehydrogenative alkynylation of the corresponding (benz)imidazoles with terminal alkynes in an open vessel.

Strong chiroptical properties from thin films of chiral imidazole derivatives allowing for easy detection of circularly polarized luminescence

“…For the synthesis of 2 , a C-5 regioselective Pd-catalyzed direct arylation was firstly performed on 1-methyl-1 H -imidazole, followed by a Pd-catalyzed dehydrogenative alkynylation at the C-2 position. 59,60 Finally, compound 3 was prepared via a Pd- and Cu-assisted C-2 direct arylation on 1-methyl-1 H -imidazole, 61 followed by alkynylation at the C-5 position with 4-ethynylbenzaldehyde through a one-pot bromination and Sonogashira coupling procedure. 62…”

Direct Decarboxylative C-2 Alkylation of Azoles through Minisci-Type Coupling

“…A striking example of radical C–H functionalization for the formation of new Csp 2 –Csp 3 bonds is undoubtedly the Minisci reaction, whose original protocol was developed for the alkylation of electron-poor six-membered heteroaromatic rings (e.g., pyridine and quinoline moieties) with alkyl-carboxylic acids as a radical precursor, in the presence of a chemical oxidant and sub-stoichiometric amounts of silver nitrate. − With the advent of novel synthetic techniques, such as photo- and electrochemistry, the Minisci protocol has been deeply revisited, assessing the development of a great number of parent transformations (Minisci-like reactions) − (Figure b). However, the radical Minisci-like alkylation involving electron-rich azoles with no substrate pre-functionalization and nucleophilic radicals still remains less developed, being limited to few examples and often requiring elevated temperatures, very long reaction time, and complementary protocols involving specific devices and/or expensive (photo)­catalysts. ,, For this reason, we decided to investigate, as part of our research on the selective functionalization of azole rings, − the possible extension of the Minisci reaction to the C-2 alkylation of electron-rich azoles. In this communication we report the results and limitations of a protocol for the fast and selective C-2 selective alkylation of electron-rich azoles with nucleophilic radicals (Figure c).…”