Phosphorous containing functional groups are underexplored as medicinal chemistry motifs. Phosphonate and phosphate groups have been deployed in pro-drugs to facilitate cell membrane permeability, 36 while phosphine oxides are only recently becoming more extensively examined following the approval of Brigatinib. There is an increasing interest in the incorporation of these motifs into drug-like molecules to modulate LogD and solubility. We hypothesized that alkyl phosphite reagents could be utilized to trap the oxetane carbocation and provide the corresponding phosphorylated oxetane products. We expected the liberated fluoride to effect dealkylation in an Arbuzov mechanism to reveal the P=O bond. Triethylphosphite successfully reacted in this manner with PMP OSF 1 to form oxetane phosphonate 80 (Scheme 2c). Improved yields were afforded by performing the reaction in the absence of K2CO3, supporting the dealkylation by the released fluoride (Scheme 2c, inset table). Trialkyl phosphites reacted to provide a variety of methyl (78), ethyl (80, 84, 85), and isopropyl (79) oxetane-phosphonates in good yields. Phosphonites were well tolerated and afforded the corresponding phosphinates in good yields (81, 82). Bulky methoxydiphenylphosphine provided phosphine oxide (83). Secondary phosphine oxides were found to react through the oxygen rather than the phosphorous, confirmed by the small molecule X-ray crystal structure of 87. In solution secondary phosphine oxides exist in equilibrium with their phosphinous acid form, which is presumably trapped through the oxygen atom preferentially by the oxetane carbocation, with oxidation to provide the more stable P(V) products observed.