ROLE OF PHOSPHORUS ADDUCTS IN THE INDOLIZATION REACTION BETWEEN ARYLHYDRAZONES AND PHOSPHORUS TRICHLORIDE

Article abstract of DOI:10.1016/S0040-4020(01)86881-2

The reaction between arylhydrazones and PCl3 can give both diazaphospholes and indoles, via a common hypothetical diazaphospholine intermediate.The product ratio depends on the reaction conditions.In particular when a solvent which dissolves the phosphorus adducts is employed, indole is the almost exclusive reaction product.A mechanism is suggested for the whole indolization reaction.It involves an acid promoted cleavage of the P-N bond of the diazaphospholine to give intermediates similar to those of the accepted Fischer indolization mechanism, where the dichlorophosphino group, substituting a hydrogen atom should have an important ro le in promoting of the loss of the amino group in the last stage of the reaction, via a "Wittig-like" elimination of Cl2PNH2.