Pyridylphosphonate derivatives

Addition of phosphorus nucleophiles to electron-poor aromatic sp carbons, followed by elimination, is a basis for the reactions in which pyridylphosphonate derivatives of dinucleotides were obtained (Schemes 47.44 and 47.45). The pyridine ring can be activated to nucleophilic attack by an appropriate substituent on the nitrogen atom. When the bulky triphenylmethyl (trityl) group was used for this... 

Pyridylphosphonic acid derivatives (68) have been prepared by addition of dialkyl phosphite anion to A-alkoxypyridinium salts. Similar compounds, it is reported, are formed from trialkyl phosphites with... 

The synthesis of nucleoside-derived pyridylphosphonates under metal-free conditions was reported (Scheme 4.216) [355]. The chemistry was operationally straightforward and entailed treatment of a nucleoside-derived secondary phosphite with pyridine/trityl chloride and DBU to generate the arylphosphonates in excellent yields. It was noteworthy that the reaction was regioselective for substitution at the 4-position of the pyridine moiety. Based upon an investigation of potential intermediates, the mechanism was proposed to proceed through the initial generation of an A-tritylpyridinium ion. Reaction of this species with the secondary phosphite and DBU afforded a dihydropyridine intermediate that could be observed by NMR spectroscopy but could not be isolated as it underwent conversion... 

A system for the preparation of nucleoside-derived 2-pyridylphosphonates using a preformed pyridinium salt as the source of the pyridine fragment has been developed (Scheme 4.217) [357], The base used for the reaction was DBU, and simply stirring the pyridinium salt with the secondary phosphite and DBU in acetonitrile at room temperature afforded the arylphosphonate in excellent yields. The phosphonylation was selective for the 2-position. The mechanism for this transformation was similar to the one proposed... 

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