| Abstract: | α-formylpyrroles substituted on the nitrogen atom by groups of increasing steric hindrance show no significant modification in the value of their stereospecific 5J coupling constants. In the i.Pr-1 and s.Bu-1 formyl-2 pyrroles, the existence of a preferential conformation has been shown. Studies of rotational barriers indicate a twist only for the t.Bu-1 formyl-2 pyrrole molecule. The stability of the 5J value relative to this last compound is attributed to a relay of the σ—σ mechanism by a σ—π transmission. |
