A linear pentapyrrole bearing α-hydroxymeythyl group in the terminal was synthesized by the stepwise coupling of α-free pyrrole with azafulvenium ion 6. When it was treated with a catalytic amount of p-toluensulfonic acid under anaerobic condition, followed by aerial oxidation of the products, a statistical mixture of uroporphyrin I-IV octamethyl esters was obtained. It is proposed that this transformation proceeds through a spiro-pyrrolenine as a key intermediate. (C) 2000 Elsevier Science Ltd.
Okada, K., Takakura, H., Nomura, K., & Saburi, K. (2000). Synthesis of a linear α-hydroxymethyl-pentapyrrole derivative and its cyclization to uroporphyrinogens. Tetrahedron Letters, 41(16), 2915–2918. https://doi.org/10.1016/S0040-4039(00)00293-8