Due to our inability to purify 3, we turned our investigation to Meisel's 18 analogous pyridine adduct, 5 (Figure ). Heating (P2O5)∞ and pyridine in acetonitrile to near reflux for 24 hours results in a fine white precipitate. The product is very poorly soluble in pyridine, chloroform, and dichloromethane, but multinuclear NMR spectroscopy gives no evidence for the pyridine analog of 4. However, a disparity between expected and observed elemental analysis data for 5 suggests the possibility of impurities analogous to 4 that are too insoluble to observe. The synthesis of 5 is easily performed on a 5 gram scale in 77% yield from two very inexpensive and commercially available reagents, providing trivial access to this diphosphorylation reagent. In the pursuit of a more soluble and spectroscopically pure N-donor base adduct of P2O5, we similarly investigated the reaction of (P2O5)∞ with triethylamine, tributylamine, 4-tertbutylpyridine, and DMF (dimethylformamide). A rapid reaction was observed in all cases, yielding more soluble products than in the case of DABCO and pyridine (see SI). However, these reactions all produced significant side products, and we chose 5 to explore further phosphorylation chemistry. Treatment of 5 with DABCO led to rapid formation of a mixture of 3 and 4. To investigate whether 4 is formed in this reaction or if an insoluble pyridine analog was present in the starting 5, we also treated 5 with DBU. This reaction resulted in clean formation of the DBU adduct, 6 (Figure ). Compound 6 is freely soluble in DCM and contains no significant impurities. However, we observed no reactivity between 6 and simple nucleophiles such as methanol and O-phenylenediamine.