Synthesis of a linear alpha-hydroxymethyl-pentapyrrole derivative and its cyclization to uroporphyrinogens

A linear pentapyrrole bearing alpha-hydroxymeythyl group in the terminal wa s synthesized by the stepwise coupling of alpha-free pyrrole with azafulven ium ion 6. When it was treated with a catalytic amount of p-toluensulfonic acid under anaerobic condition, followed by aerial oxidation of the product s, a statistical mixture of uroporphyrin I-IV octamethyl eaters was obtaine d. It is proposed that this transformation proceeds through a spiro-pyrrole nine as a key intermediate. (C) 2000 Elsevier Science Ltd. All rights reser ved.