Synthesis and structural aspects of N-triflylphosphoramides and their calcium salts'highly acidic and effective Brønsted acids

Recently, 1,1′-bi-2-naphthol (BINOL)-based N-triflylphosphoramides emerged as a new class of potent Brønsted acid catalysts. In this paper we describe the efficient synthesis of various BINOL-based N- triflylphosphoramides and their calcium salts. Furthermore, X-ray crystal structure analysis combined with energy-dispersive X-ray spectroscopy (EDX) measurements confirmed that the synthesised chiral N-triflylphosphoramides are highly acidic metal-free catalysts. Freedom! The synthesis and structure determination of various 1,1′-bi-2-naphthol (BINOL)-based N-triflylphosphoramides and their corresponding calcium salts is presented. A simple acidic treatment of the calcium salts provides the metal-free Brønsted acids (see scheme; Tf=trifluoromethanesulfonyl).