| Budget Amount *help |
¥14,600,000 (Direct Cost: ¥14,600,000)
Fiscal Year 2000: ¥2,700,000 (Direct Cost: ¥2,700,000)
Fiscal Year 1999: ¥11,900,000 (Direct Cost: ¥11,900,000)
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| Research Abstract |
One of the unsolved problems in the field of Lewis acid-catalyzed stereoselective reactions is the development of chiral Lewis acid catalysts which are tolerant to strongly coordinating nucleophiles and applications to organic synthesis. From this standpoint, we have developped a variety of transition metal complexes of 4, 6-dibenzofurandiyl-2, 2'-bis(4-phenyloxazoline)(R, R-DBFOX/Ph) and the copper(II) complex of isopropylidene-2, 2'-bis[4-(o-hydroxybenzyl)oxazoline] (R,R-BOX/o-HOBn) and utilized to the catalyzed asymmetric conjugate additions of O-benzylhydroxylamine, malononitrile, and cyclic 1, 3-diketones. The floowing results have been obtained.
1. Enantioselective Conjugate Additions of a Hydroxylamine : The copper(II) complex of R, R-BOX/o-HOBn was found to act as an efficient chiral Lewis acid catalyst in conjugate addition reactions of O-benzylhydroxylamine. 1-Crotonoyl-3-isopropyl-2-imidazolidinone was the best acceptor which provided the maximum enantioselectivity up to 97%
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ee when the reaction was performed in a dilute condition (0.03 M) at -40℃. Acceptor molecules having a variety of substituents at β-position can be successfully employed showing that this reaction proves to be useful and convenient access to enantiomers of β-amino acid delivertives.
2. Enantioselective Conjugate Additions of Malononitrile : In the reactions of malononitrile activated by a catalytic amount of 2, 2, 6, 6-tetramethylpiperidine (TMP) with 3-crotonoyl-2-oxazolidinone activated by the nickel(II) aqua complex of R, R-DBFOX/Ph, the corresponding Michael adduct was produced in enantioselectivities up to 94% ee. This reaction provides the first successful example for the double activation type catalyzed asymmetric reactions in which both of acceptor and donor molecules have been activated separately by Lewis acid and base catalysts.
3. Enantioselective Cyclobutanone Formation Reactions : It has been found that, when 1, 3-cyclohexanedione activated by a catalytic amount of 2, 2, 6, 6-tetramethylpiperidine (TMP) was reacted with 1-crotonoyl-3, 5-dimethylpyrozole activated by the nickel(II) aqua complex of R, R-DBFOX/Ph, the corresponding spiro cyclobutanone is produced in enantioselectivities up to 96% ee. Both acid and base catalysts are essential and the pyrrazole acceptors are especially efficient for the formation of cyclobutanones. Less
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