DABCO as a practical catalyst for aromatic halogenation with N-halosuccinimides

Abstract

An efficient and mild system for the aromatic halogenation using DABCO, a simple, cheap and easy of handling Lewis base, as the catalyst is reported.

Solid-state mechanochemical cross-coupling of insoluble substrates into insoluble products by removable solubilizing silyl groups: uniform synthesis of nonsubstituted linear oligothiophenes

“…1). A dilute solution of bis-silylated terthiophene (14) in chloroform showed strong blue emission with the maximum emission wavelength (l em, max ) at 449 nm, excited by UV light (l ex = 370 nm). A clear red shi in luminescence was observed with the elongation of the thiophene units.…”

“… 11 This choice was motivated by the following reasons ( Scheme 2B ): (1) the cross-coupling of halogenated oligothiophenes (>5 mers) is inefficient due to their significantly low solubility in organic solvents; 11 (2) practical strategies for the uniform and systematic synthesis of relatively long linear oligothiophenes (>5 mers) are rare; 11 (3) a silyl-based solubilizing group can be easily installed into thiophene-based boron nucleophiles via an iridium-catalyzed C–H silylation protocol; 12 (4) desilylation of 2-silyl-substituted thiophenes is feasible under mild conditions; 13 (5) an electrophilic bromination selectively occurs at the alpha-position of the sulfur atom. 14 This mechanochemical strategy should enable the uniform synthesis of nonsubstituted linear oligothiophenes with various lengths and a diverse range of its derivatives, even if insoluble substrates and products are involved. Although Bäuerle et al have reported the solution-based synthesis of 3D oligothiophene dendrons via an iterative synthetic approach using desilylation/cross-coupling sequences, the synthesized nonsubstituted 3D-dendrimeric oligothiophenes are soluble in organic solvents, and the insolubility of starting materials and reaction products was not a problem in their study.…”

Visible light-enabled regioselective chlorination of coumarins using CuCl2via LMCT excitation

“…N -Halosuccinimide (NXS, X = Cl, Br, I) is the most popular alternative halogenating reagent to replace molecular halogens. 5 However, for less electron-rich substrates, the activation of NXS using a Brønsted acid, 6 Lewis acid 7 or Lewis base 8 is usually a pre-requisite for effective halogenation. In recent years, visible light photocatalysis has emerged as a versatile strategy to promote many organic reactions under mild conditions with better selectivity.…”

Automated grindstone chemistry: a simple and facile way for PEG-assisted stoichiometry-controlled halogenation of phenols and anilines using N-halosuccinimides

“…In recent time, the use of Lewis or Brønsted acids, Lewis bases, and transition-metal catalysts (Pd, Rh, Fe, etc.) were em-ployed to boost the reactivity of NXS (Scheme 1b) [32][33][34][35][36][37][38][39][40][41][42][43]. However, the use of toxic and expensive metals, high catalyst loading, and heating conditions are some sheer hurdles to achieving sustainability.…”