Biosynthesis of porphyrins and related macrocycles.: Part 48.: The rearrangement of 2H-pyrroles (pyrrolenines) related to the proposed spiro-intermediate for porphyrin biosynthesis

It is proposed that the biosynthesis of uroporphyrinogen III 3, the parent precursor of the natural porphyrins, chlorins and corrins, involves a 2N-pyrrole (pyrrolenine) 2 as a key intermediate, Model pyrrolenines have now been used to show that (a) pyrrolylmethylpyrrolenines, e.g. 32, readily undergo rearrangement in a way which matches that suggested in the biosynthetic proposal; (b) there is regioselectivity in the rearrangement which also parallels that required for the biosynthesis of uroporphyrinogen III. This work adds further support to the biosynthetic proposal by showing that all the required chemistry is both feasible and facile.