ortho effect on the nitrosation of the 2,3-diphenyl-5(2-methoxyphenyl)pyrrole

A comparison of the behaviour on the nitrosation of the isomers 5-(2-methoxyphenyl)- ( 1a ) 5-(3-methoxyphenyl)- ( 1b ) and 5-(4-methoxyphenyl)2,3-diphenylpyrroles ( 1c ) carried out in the usual way with iso-amyl nitrite in a solution of sodium ethoxide in ethanol evidences that 1a is dramatically less reactive with respect to 1b and 1c . The different reactivity was ascribed to the occurrence of a strong hydrogen bond involving pyrrole N? H and the ortho-methoxy group.