Phosphine oxides bearing two or three 2‐pyridyl groups react with organometallic reagents affording 2,2′‐bipyridyl, 2‐substituted pyridines and pyridine in good yields. Phosphonium salts and phosphine oxides, bearing at least two 2‐pyridyl or substituted 2‐pyridyl groups also give the corresponding 2,2′‐bipyridyls and pyridines upon treatment with acid or neutral solvents such as water and alcohols in substantial yields. The 2,2′‐bipyridyls are considered to be formed by ligand coupling within the pentacoordinated phosphorus intermediate formed incipiently during the reaction.
204 ChemInform Abstract The tris(2-pyridyl)benzylphosphonium salts (I) are cleaved in neutral or acidic aqueous solutions to form the bipyridines (II), together with the pyridines (III). The yields depend on the medium, reaction temperature, and time. The bis(2-pyridyl)phosphine oxides (IV) are similarly degraded to produce (IIa) and (IIIa).
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