| 摘要 |
PROBLEM TO BE SOLVED: To obtain a new optically active oxazaborolidine enabling optically active aldols excellent in optical purity to be synthesized when used as a Lewis acid by reacting specific optically active aminoalcohols with boron trichloride. SOLUTION: This new optically active oxazaborolidine is expressed by formula I (wherein, R1-R3 are each H, a lower alkyl, or the like, except the case that all of R1-R3 are H; R4 and R5 are each an aryl which may have a substituent of a lower alkyl or a lower alkoxy, or the like; R6 is a lower alkyl which may have a substituent of F or Cl, or the like; * is an asymmetric carbon). The compound of formula I can be obtained by reacting optically activeβ- aminoalcohols of formula II with boron trichloride. Optically active aldols can simply and easily be synthesized by reacting ketene silyl acetals of formula III (wherein, R7 is a lower alkyl; R8 and R9 are each a lower alkyl or H) with aldehydes of formula IV (wherein, R10 is H, a lower alkyl, a halogen, or the like) in the presence of the compound of formula I.
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