We report herein sharp physical evidence, i.e., single-crystal X-ray diffraction and ¹H-NMR spectral data, confirming that quaternary ammonium species interact with anions via a set of directional ion–dipole cooperative ⁺N-C-H unusual H-bonding interactions and not via pure non-directional ionic electrostatic interactions. This finding, which has been often invoked by calculations, is herein substantiated by the preparation of two model compounds and an analysis of their X-ray crystal structures in the solid state and ¹H-NMR spectra in solution. These observations are particularly pertinent for the rational design of novel catalyses and catalysts and providing guidance to an understanding of these species in solution and during asymmetric enantioselective catalysis.

Indole moiety is well-known as a superlative framework in many natural products and synthetic pharmaceuticals. Herein, we report an efficient procedure to synthesize a series of functionalized 2-methyl-1H-indole-3-carboxylate derivatives from commercially available anilines properly functionalized by different electron-withdrawing and -donating groups through a palladium-catalyzed intramolecular oxidative coupling. The conversion of a variety of enamines into the relevant indole was optimized by exposing the neat mixture of reactants to microwave irradiation, obtaining the desired products in excellent yields and high regioselectivity. The synthesized compounds were confirmed by ¹H and ¹³C spectroscopic means as well as by high-resolution mass spectrometry.

Herein we report the first organocatalysed enantioselective synthesis of gingesulfonic acids and shogasulfonic acids via a mild and convenient aminothiourea-catalysed conjugate addition of bisulfite to the olefin moiety of α,β-unsaturated carbonyls—a technology previously reported by us. A series of optically active naturally occurring sulfonic acids are prepared in their natural and unnatural configurations, and their absolute configurations are unequivocally confirmed by single crystal X-ray diffractometry.