Porphyrin twin-coronet

Oxometalloporphyrins were taken as models of intermediates in the catalytic cycle of cytochrome P-450 and peroxidases. The oxygen transfer from iodosyl aromatics to sulfides with metalloporphyrins Fe(III) or Mn(III) as catalysts is very clean, giving sulfoxides, The first examples of asymmetric oxidation of sulfides to sulfoxides with significant enantioselectivity were published in 1990 by Naruta et al, who used chiral twin coronet iron porphyrin 27 as the catalyst (Figure 6C.2) [79], This C2 symmetric complex efficiently catalyzed the oxidation... 

Naruta et al. [225, 226] designed the twin-coronet porphyrin ligands (62) and (63) with binaphthyl derivatives as chiral substituents (Figure 13). Each face of the macrocycle is occupied by two binaphthyl units and the ligand has C2 symmetry. Iron complexes of these compounds can be very effective catalysts in the epoxidation of electron-deficient alkenes. Thus, nitro-substituted styrenes are readily epoxidized in 76-96% ee [226]. The degree of enantioselectivity can be explained on the basis of electronic interactions between the substrate aromatic ring and the chiral substituents rather than on the basis of steric interactions. 

Figure 13 Structures of twin-coronet porphyrins. Reproduced from J. Am. Chem. Soc., 113, 6865 (1991) by permission of the American Chemical Society...

Matsui, E., Y. Naruta, F. Tani, and Y. Shimazaki (2003). An active-site model of prostaglandin H synthase An iron twin-coronet porphyrin with an aryloxyl radical overhang and its catalytic oxygenation of 1,4-diene. Angew. Chem. Int. Edit. 42, 2744-2747. 

The utilization of chiral binaphthyl groups was further demonstrated by Naruta et aL [289, 293-295] and Kodadeck et al [296]. By employing electron rich "Twin Coronet" porphyrin complexes (Fig. 11(c)), Naruta observed very high ee value (89%) for 2-nitrostyrene oxide. The correlation of optical yields with substituent a of styrene derivatives is suggestive of the charge transfer interaction between the styrene derivatives and the binaphthylene moieties in the fixation of the substrates and the recognition of their prochiral faces [292]. 

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