Although the hydrolysis reaction to generate 3 is very facile, it does require prior synthesis and isolation of heterocycle 1. This heterocycle is synthesised by the cycloaddition of the activated alkyne to a free azophosphine, the latter of which is produced by the deprotection of the azophosphine-borane MesN2P i Pr2.BH3 (A; see Scheme S1 in Section S1.7 of the ESI). To enable simple access to the desired pyraolyl-phosphine oxides, we devised a one-pot approach directly from the air-stable precursor A (Scheme 2, and Scheme S2 in the ESI). The one-pot approach precludes the need to isolate the azophosphine and heterocycle intermediates, which significantly reduces the amount solvent used and removes the silica required for chromatography. Furthrmore, the total yield of 3 via the one-pot method was higher than the combined yields of the step-wise approach (65% vs 48%).