Pyrroles and related compounds-XXXIV. Acrylic esters in the porphyrin series

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Treatment of imidazolylporphyrins (12) with sodium borohydride in methanol affords high yields of the corresponding hydroxymethylporphyrins (14) which can be oxidised with chromium trioxide in pyridine to give high yields of formylporphyrins (11). When heated with methyl hydrogen malonate in pyridine, good yields of porphyrin trans-acrylic esters (15) are produced; a milder method involving reaction of the formylporphyrin (11a) with a phosphonium ylid (20) or better, a phosphonate ester (21), gives good yields of the porphyrin trans-acrylic ester (16a). Porphyrin β-keto-esters (e.g. 8b) are reduced with sodium borohydride in methanol, to give the 6-hydroxypropionate ester (17b); prolonged treatment with borohydride results in over-reduction at the 7-propionate side-chain. The hydroxypropionate porphyrin (17b) is readily dehydrated to give a high yield of the porphyrin trans-acrylic ester (15b). Methods for the magnesiation and preparation of β-keto-ester and trans-acrylic ester porphyrin 7-propionic acids are described; hydrolysis of porphyrin β-keto-esters (e.g. 8b) can be controlled such that only the propionic function is hydrolysed. However, prolonged alkaline hydrolysis and re-esterification furnishes a mixture of 2-vinylrhodoporphyrin-XV dimethyl ester (9b) and the 2-vinyl-6-acetylporphyrin (18b). The latter porphyrin can also be prepared by treatment of the acid chloride (10b) from 2-vinylrhodoporphyrin-7-methyl ester with sodio di-t-butyl malonate, followed by treatment with trifluoroacetic acid. © 1976.

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