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.