| Budget Amount *help |
¥4,400,000 (Direct Cost: ¥4,400,000)
Fiscal Year 1986: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 1985: ¥3,100,000 (Direct Cost: ¥3,100,000)
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| Research Abstract |
The main results of this project are summarized as follows.
(1) Asymmetric [2,3]-Wittig rearrangement involving chiral lithium and potassium azaenolate termini generated from chiral 2-oxazolines have been investigated. We found that these rearrangements provided relatively high optical yields (78-95% ee). During these studies, we have observed interesting influences of the countercation (Li vs. K) and their complexation with a crown ether. Furthermore, the asymmetric reaction has successfully been applied to the chiral synthesis of unnatural verrucarinolactone.
(2) Asymmetric [2,3]-Wittig rearrangement involving chiral amide Li- and Zr( <IV> )-enolate termini generated from the prolinol- and valinol-derived amide systems has been studied. Unfortunately, these asymmetric variants have been found to provide only moderate levels of asymmetric induction. Interestingly, however, the Zr-enolate variant has been shown to the opposite sense of diastereofacial selection to that of the Li-enolate
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counterpart.
(3) Asymmetric [2,3]-Wittig rearrangement involving chiral ester enolate termini generated from the 8-phenylmenthol-derived chiral ester system has been investigated in details. First, we have found that the Li-enolate rearrangement provides an extremely high optical yields (>95% ee) along with a high erythro-selectivity (>90%). Thus, this type of asymmetric rearrangement offers an efficient method for chiral synthesis of <alpha> -hydroxy- <beta> -alkyl carboxylic acid derivatives. Its efficiency has been demonstrated within the simple chiral synthesis of verrucarinolactone. Second, the rearrangement involving Ti( <IV> )- and Sn( <IV> )-enolates generated from the silyl enol ether via transmetalation has been found to exhibit very low levels of asymmetric induction. Third, the rearrangement involving Zr( <IV> )-enolate generated from the Li-enolate via transmetalation, by contrast, provides a high optical yield comparable to that of the Li-enolate counterpart.
On the basis of these results described above, we have discussed and elucidated the structures of the metal enolates involved in the [2,3]-Wittig rearrangements. Less
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