Bonellin dimethyl ester

Intramolecular Friedel-Crafts acylation has been observed with bonellin dimethyl ester (20).53 The reaction proceeds in contrast to corresponding porphyrins, very smoothly with concentrated sulfuric acid because the propanoic acid side chain at the sp3 center is located above the macrocyclic ring system and therefore can better fulfill the stereoelectronic requirements for the ring-closure reaction. The ring closure is accompanied by racemization in the product 21. 

Cyclization to the benzo[c]phenanthridine (127) competes with rearrangement to the ring-expanded product (128) on irradiation of the amine oxide (129). A practical synthesis of the chlorin macrocycle (130) has been developed by irradiation of the seco-compound (131) in tetrahydrofuran containing TFA and Hiinig s base this is thought to take place by photocyc-lization of the ISrr-tautomer (132), followed by elimination of methanol. Analogous approaches have been employed in the syntheses of ( )-bonellin dimethyl ester and 20-methyl- and 20-cyano-isobacteriochlorins. " ... 

Battersby AR, Dutton CJ, Fookes CJR (1988) Synthetic studies relevant to biosynthetic research on vitamin B12. Part 7. Synthesis of (-h/—)-bonellin dimethyl ester. J Chem Soc Perkin Trans 1, 1569... 

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