Construction of Novel Chiral Host Molecule Systems Utilizing meso-Carbon Bridged Porphyrin Dimers and Their Application to Organic Synthesis

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A broad range of topics of porphyrin chemistry including construction of novel and synthetically useful chiral host molecule systems utilizing meso-carbon bridged porphyrin dimers were studied. The results obtained are briefly summarized as follows.(1) Catalytic and regio-and stereoselective rearrangement of epoxides to aldehydes via an alkyl migration can easily be achieved with a high valent metalloporphyrin complex, Cr(tpp)OTf, at a low catalyst loading. Since we have previously reported that Fe(tpp)X catalyzes the rearrangement of epoxides to ketones via a hydrogen mygration, ketones and aldehydes can selectively be prepared from epoxides in a highly controlled manner by the simple choice of Fe(III) and Cr(III) as a central metal ion of the porphyrin catalysts.(2) A novel and efficient recyclable catalyst system can now be realized using a phthalocyanine-based Lewis acid catalyst, Cr(PC)OTf, that can effectively promote the regio-and stereoselective rearrangement of epoxides to ald … More ehydes. This recyclable catalyst system provides an operationally simple, practical way for synthesizing optically active aldehydes from epoxides.(3) The porphyrin-based Lewis acid catalyst can effectively accelerate the rearrangement via a concerted [3,3] pathway with a minimal degree of bond ionization of the substrates, providing the corresponding Claisen products in moderate to high yields and almost perfect regioselectivity at low catalyst loading. The most notable advantage of the catalyst system is its unique stereoselectivity: Cr(TPP)Cl significantly enhances reversal of E/Z selectivity in the thermal Claisen rearrangement of allyl vinyl ethers, especially, 4,5-and 4,6-disubstituted derivatives, and dose so in a catalytic fashion.(4) Palladium-catalyzed cyanation of bromoporphyrins is now realized using cyanoethylzinc bromide as a specific cyanating agent. This new protocol provides an easy access to various cyanated Zn(II) porphyrins, including meso-mono-, meso-di-, and β-mono-cyano-substituted Zn(II) complexes.(5) A facile and efficient synthesis of meso-formyl substituted porphyrins via substitution reactions of porphyrins with silylmethyllithium reagents, especially PyMe2SiCH2Li, followed by oxidation with DDQ has been developed.(6) The porphyrin dimers that adopt a pseudocofacial conformation can effectively bind a variety of organic molecules, such as amines, alcohols, and ethers, over room temperatures. We also disclosed the use of the porphyrin dimers for the direct sensing of chiral amines and alcohols based on the CD exciton chirality method. Less