Highly Regio- and Stereoselective Rearrangement of Epoxides to Aldehydes Catalyzed by High-Valent Metalloporphyrin Complex, Cr(TPP)OTf

Abstract

Chromium(III) tetraphenylporphyrin triflate, Cr(TPP)OTf, works as an efficient and characteristic Lewis acid catalyst in the regio- and stereoselective rearrangement of epoxides to aldehydes. This Cr(TPP)OTf-catalyzed reaction is an operationally simple and especially convenient method for synthesizing optically active beta-siloxy aldehydes from 2,3-epoxy silyl ethers which are readily available in enantiomerically enriched forms by the Sharpless epoxidation of allylic alcohols followed by silylation.

Catalytic, regioselective, and green methods for rearrangement of 1,2-diaryl epoxides to carbonyl compounds employing metallic triflates, Brønsted-acidic ionic liquids (ILs), and IL/microwave; experimental and computational substituent effect study on aryl versus hydrogen migration

“…These reactions typically employed DCM, THF, MeCN, and Et 2 O as solvent. A high-valent metalloporphyrin complex Cr(TPP)OTf in DCE solvent proved efficient in regio-and stereo-selective epoxide rearrangement to aldehydes [15,16].Despite the significantly greater migratory aptitude of hydrogen versus aryl, a large majority of Lewis acid-catalyzed epoxide ring opening reactions of styrene oxides and stilbene oxides result in the formation of aldehydes (aryl migration) (Fig. 1), but situations where the ketone is formed, either as minor product along with the aldehyde or as a major product, have also been reported [5].…”

“…These reactions typically employed DCM, THF, MeCN, and Et 2 O as solvent. A high-valent metalloporphyrin complex Cr(TPP)OTf in DCE solvent proved efficient in regio-and stereo-selective epoxide rearrangement to aldehydes [15,16].…”

3.16 The Semipinacol Rearrangements

“…173 On the contrary, the use of Cr(TPP)OTf lead to exclusively alkyl migration products (Scheme 129). 174 Like those of 2,3-epoxy alcohols, ring expansion and contraction will be observed in the presence of cyclic substrates. A classic example is the rearrangement of oxaspiropentanes, which give synthetically important and challenging cyclobutanones.…”

Zinc (II) [tetra(4-methylphenyl)] Porphyrin: a Novel and Reusable Catalyst for Efficient Synthesis of 2,4,5-trisubstituted Imidazoles Under Ultrasound Irradiation

“…Electron-deficient metalloporphyrins have been used as mild and non-toxic Lewis acid catalysts. [40][41][42][43][44] In continuation of our interest on the synthesis of 2,4,5-trisubsti-Javad Safari, Shiva Dehghan Khalili, Sayed Hossein Banitaba, and Hossein Dehghani tuted imidazoles, 45,46 we decided to explore ability of metalloporphyrins in the synthesis of 2,4,5-trisubstituted imidazoles for the first time. Therefore, Zinc (II) [tetra (4-methylphenyl)] porphyrin was used as a mild Lewis acid catalyst for the three-component one-step synthesis of 2,4,5-trisubstituted imidazoles by condensation reaction of 1,2-diketones or α-hydroxyketones with aromatic aldehydes and ammonium acetate under ultrasound irradiation at ambient temperature (Scheme 1).…”