Porphyrin Building Block Information and References

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  • Meso-substituted dipyrromethanes can be condensed with typical lewis acid catalysts to give a statistical mixture of 5,10 and 5,15-porphyrins, due to scrambling of the respective porphyrinogens.1 If separation is simple, this is the most direct route to these porphyrins from dipyrromethane precursors. Improved syntheses to reduce scrambling have been reported by two groups, with moderate yields of the desired 5,15-porphyrin. 2,3
  • Recent developments by Lindsey and co-workers have shown that through the use of dipyrrodicarbinols, the 5,10-porphyrins can be produced as the sole product of condensation. Yields are low to moderate (~25%). However, when aryl groups with electron withdrawing substituents are employed, yields decrease. 4
  • In order to reduce scrambling during porphyrin synthesis using dipyrromethane precursors, lewis acid catalysts other than TFA and BF 3•Et 2O have been employed. The use of InCl 3 and Yb(OTf) 3 produced the respective porphyrins in moderate yield with no detectable scrambling. 5
  • Another strategy to reduce scrambling was reported by Cammidge and coworkers. By using dipyrromethane precursors with strong electron withdrawing groups, it was possible to obtain the desired 5,15-porphyrin as the major product through direct condensation with aldehydes. 6
  • By synthesizing a dipyrromethane with a boronic ester moiety, Lindsey and coworkers were able to create a porphyrin triad through Suzuki coupling of a 5,15-diborano porphyrin (center unit) with an iodo-porphyrin (peripheral unit). 7
  • Tripyrromethane precursors have been used to produce milligram quantities of 5,10-porphyrins by condensation with dicarbinol pyrroles.8 Direct condensation of tripyrromethanes with aldehydes and pyrrole, gives a mixture of porphyrin with the desired 5,10-porphyrin being the major product, albeit in low yield.

References

  1. Treibs, N. Häberle, Liebigs. Ann. Chem., 718, 1968, p.183
  2. D. Dolphin et al., J. Porphyrins Phthalocyanines, 2, 1998, p.455
  3. J.S. Lindsey et al., J. Org. Chem., 64, 1999, p.2864
  4. J.S. Lindsey et al., J. Org. Chem., 65, 2000, p.7323
  5. J.S. Lindsey et al., J. Porphyrins Phthalocyanines, 5, 2001, p.810
  6. Cammidge, O. Öztürk, J. Org. Chem., 67, 2002, p.7457
  7. J.S. Lindsey et al., Tetrahedron, 57, 2001, p.9285
  8. C-H Lee et al., Tet. Lett., 37, 1996, p.197
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