The initial optimization allowed us to identify the optimal conditions that afforded desired -aminophosphonate 2 in 76% isolated yield. The reaction was performed with 2 mol% Ir(p-Meppy)3 as the photocatalyst, 3.0 equiv P(OMe)3 in MeCN (0.1 M), and irradiation by a 40W 456 nm LED for 12 h (Table , entry 1). Lower loading of the phosphite reagent (entry 2) or the photocatalyst (entry 3) led to decreased reaction efficiency. Less reductive photocatalyst, fac-Ir(ppy)3, 17 could also promote the phosphonylation of 1, albeit with a lower yield (entry 4). The phosphonylation can be conducted under air without loss in reaction efficiency (entry 5). However, the reaction is sensitive to moisture, as sluggish reaction was observed when H2O was added as an additive (entry 6), probably due to the hydrolysis of trimethyl phosphite. Prolonged reaction time didn't further improve the yield of 2 (entry 7). Control experiments showed that both the photocatalyst (entry 8) and light irradiation (entry 9) were essential to the success of the phosphonylation. For detailed optimization studies, please refer to Supplementary Section S3.