Phosphole, pentaphenyl

Phosphol-1-oxide, z.B. 1,2,5-Triphenyl- bzw. 7,2,3,4,5-Pentaphenyl-phosphol-1-oxid oder das in situ herstellbare 2-Phenyl-2H-2-benzophosphol-2-oxid, konnen als reaktive Diene mit geeigneten Dienophilen eine [4 + 2]-Cycloaddition eingehen. Beispielsweise... 

This was the first approach used for the synthesis of a monocyclic phosphole, the pentaphenyl derivative, and stands as a landmark in heterocyclic phosphorus chemistry. In 1959, two laboratories reported the synthesis of this compound. In one synthesis, the dilithio derivative of tetra-phenylbutadiene was reacted with phenylphosphonous dichloride (Scheme 61) the reaction proceeded in excellent yield (84% <59JA3163,60JA5099 . Since the starting diene is easily prepared from diphenylethyne and lithium, it remains the best way to prepare this derivative, which has found use in many subsequent studies. In addition to the P-phenyl derivative, the P-benzyl compound was also reported (38% <6UA4406 . 

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