Enantioselective synthesis of ammonium cations.

Control of molecular chirality is a fundamental challenge in organic synthesis. Whereas methods to construct carbon stereocentres enantioselectively are well established, routes to synthesize enriched heteroatomic stereocentres have garnered less attention. Of those atoms commonly present in organic molecules, nitrogen is the most difficult to control stereochemically.

Nucleophilic displacement reactions of 5'-derivatised nucleosides in a vibration ball mill.

Vibration ball-milling in a zirconia-lined vessel afforded clean and quantitative nucleophilic displacement reactions between 4-methoxybenzylthiolate salts and nucleoside 5'-halides or 5'-tosylates in five to 60 minutes. Under these conditions, commonly-encountered nucleoside cyclisation byproducts (especially of purine nucleosides) were not observed. Liquid-assisted grinding of the same 5'-iodide and 5'-tosylate substrates with potassium selenocyanate in the presence of DMF produced the corresponding 5'-selenocyanates in variable yields over the course of between one and eleven hours thereby avoiding the preparation and use of hygroscopic tetrabutylammonium salts.