98(P-32) シクロプロピルアミン類の触媒的不斉合成とその応用(ポスター発表の部)
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As a C2 symmetric hydrophilic chiral ligand, a series of 2,6-bis(oxazolinyl)-pyridines (pyboxs) bearing a hydroxyalkyl group on the oxazoline ring has been synthesized from readily available amino acid derivatives. Catalytic asymmetric intermolecular cyclopropanation of electron rich terminal alkenes such as vinyl ethers and enamines with diazoesters in the presence of hydrophilic pybox ligand, pybox-hm and Ru(II) complex proceeded smoothly in protic or biphasic media to give the corresponding cyclopropanation products in 97:3 to 99:1 trans/cis ratios and 90 to 97% ee. Steric tuning of the chiral environment of pybox ligands was simply achieved by using a weak interaction between the solvent and the hydroxyl groups of the chiral ligand. The solubility of the new hydrophilic pybox and Ru(II) complexes in protic solvents is dramatically increased; hence, the efficiency of these catalysts enhanced the rate of cyclopropanation. Furthermore, the active catalyst in the water phase can be re-used several times for the cyclopropanation reaction. The hydroxymethyl derivative of pybox can provide excellent stereoselectivities for cyclopropanations of electron rich terminal alkenes, compared to the hydroxyethyl or isopropyl derivatives, in moderate yields in aqueous and protic media. We hypothesize that appropriate solvation of water or alcohols around the hydroxy group causes a more favorable chiral environment around the active site for the cyclopropanation. Work is now under way on applications for total synthesis of natural product, Belactosin A performed in aqueous media.
- 2003-09-01
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関連論文
- 98(P-32) シクロプロピルアミン類の触媒的不斉合成とその応用(ポスター発表の部)
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