Chiral monoaza-15-crown-5 lariat ethers synthesized from D-glucose, D-galactose, and D-mannitol have been applied as phase-transfer catalysts in the enantioselective epoxidation of chalcones with tert-butylhydroperoxide. The type of monosaccharide on the crown ether and the substituents at the nitrogen atom of the crown-ring has a major influence on both the chemical yield and enantioselectivity. Among the catalysts, the crown ether annellated to methyl-4,6-O-benzylidene-alpha-D-glucopyranoside, with 3-hydroxypropyl side arm at the nitrogen atom 1f proved to be the most effective (92% ee). The enantioselectivity was also affected by the substituents on the aromatic rings of the chalcone. The absolute configurations of epoxyketones 6a, 6b, 6d, 6i, 6k, and 6m were determined by CD spectroscopy; the complete stercostucture of 615 was determined by single crystal X-ray analysis. (C) 2004 Elsevier Ltd. All rights reserved.
Bovine Bone Derived Natural Nanocrystalline Hydroxyapatite Supported Boron Trifluoride: An Efficient, Recyclable, and Eco-Friendly Heterogeneous Catalyst for Diastereoselective Formation of α-Hydroxy-β-methoxyketones
作者:Ali Saffar-Teluri
DOI:10.1080/15533174.2014.900638
日期:2016.1.2
Catalytic ring opening reactions of -epoxyketones by boron trifluoride supported on natural nanocrystalline hydroxyapatite as a heterogeneous, reusable, and highly efficient catalyst in methanol solution at room temperature resulted in the formation of -hydroxyl--methoxyketones through C-O cleavage in excellent yields. The catalyst can be easily separated and reused for several circles.