Metalloporphyrin complexes, such as Cr(TPP)X, Fe(TPP)X, and Yb(TPP)X, work as an efficient Lewis acid catalyst with a unique reaction-field that can promote the regio- and stereoselective rearrangement of epoxides to carbonyl compounds. Compared to other Lewis acid reagents and catalysts reported so far, these porphyrin-based catalysts have several advantages as follows: (1) These catalysts are stable crystalline solids more convenient to handle; (2) effective loading of the catalyst is generally less than 2% for the rearrangement; and (3) high yields and almost complete regio- and stereoselectivity can easily be achieved by these porphyrin-based catalysts.α,β-Epoxyketones are selectively transformed into the corresponding 1,2-diketones with a metalloporphyrin complex Fe(TPP)OTf. Ketones and aldehydes can selectively be prepared from the same di- and trisubstituted epoxide by the choice of Fe(III) and Cr(III) ions, respectively, as the central metal ion of the porphyrin catalysts. A metallophthalocyanine complex, Cr(TBPC)OTf is further efficient Lewis acid catalyst with an excellent reusability for the rearrangement of epoxides to aldehydes, thus the phthalocyanine-based catalyst enables the practical synthesis of enantioenriched aldehydes bearing a stereogenic quaternary carbon centre from optically active trisubstituted epoxides.
2009 社団法人 有機合成化学協会