443755-02-0Relevant articles and documents
The rational synthesis of chlorins via rearrangement of porphodimethenes: Influence of β-substituents on the regioselectivity and stereoselectivity of pyrroline ring formation
Burns, Dennis H.,Li, Yue H.,Shi, Dong C.,Caldwell, Timothy M.
, p. 4536 - 4546 (2007/10/03)
The porphodimethene rearrangement methodology reported in this paper provides for a rational, step-by-step synthesis of chlorins from readily available pyrrole precursors. The intermediate porphodimethenes are furnished directly via the '2 + 2' MacDonald condensation, or by the less symmetry-constrained '3 + 1' condensation of a tripyrrane and bis-formyl pyrrole. The synthetic route is short and highly convergent, especially in the case of the '3 + 1' approach, and furnishes chlorins in good to moderate yields. The synthesis is highly regioselective and appears to be based on the ability of the β-substituent to stabilize excess electron density, with an electron-neutral hydrogen or an electron-withdrawing carbonyl β-substituent demonstrating the greatest influence on the formation of the pyrroline ring. The synthesis is highly stereoselective when epimerization of the pyrroline ring β-carbons is possible, furnishing only the trans-reduced sterioisomer. Finally, there is substantial evidence that a fifth, axial ligand is involved in the transposition of peripheral hydrogens during the rearrangement of the π-system from metalloporphodimethene to metallochlorin.
