Synthetic studies relevant to biosynthetic research on vitamin B12. Part 1. Syntheses of C-methylated chlorins based on 1-pyrrolines (3,4-dihydropyrroles)

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Abstract
Two routes are explored for the synthesis of chlorins geminally substituted in the reduced ring; both involve cyclisations of 1-pyrroline (3,4-dihydropyrrole) systems promoted by copper(II) salts. In the preferred synthesis, a pyrrolomethyl-1-pyrroline is combined with a 5-bromo-5′-bromomethyl-pyrromethene; though not high yielding, this approach involves few steps from readily prepared building blocks.