- Stereoselective Radical Additions of γ-Oxy-α,β-unsaturated Ester Derivatives; 1,2-Asymmetric Induction in Acyclic and Cyclisation Systems
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Examination was made of 1,2-asymmetric induction in the addition of alkyl radicals to γ-oxy-α,β-unsaturated ester derivatives 1 and 2 prepared from ethyl lactate and (R)-2,3-O-isopropylideneglyceraldehyde 3, respectively.The addition reactions of hexyl, cyclohexyl and 3-phenylpropyl radicals to (Z)-2 derived from aldehyde 3 gave β-addition products with syn-stereoselectivity (syn:anti = 8.6:1 - syn only).The reactions of (E)-2 were non-stereoselective.Based on allylic strain, a transition-state model for the syn-stereoselectivity is proposed. 1,2-Asymmetric induction was carried out in radical cyclisation to synthesize optically active cyclohexane derivatives.
- Morikawa, Tsutomu,Washio, Yoshiaki,Harada, Susumu,Hanai, Ryo,Kayashita, Takashi,et al.
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- Highly Selective Synthesis of Z-Unsaturated Esters by Using New Horner-Emmons Reagents, Ethyl (Diarylphosphono)acetates
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New Horner-Emmons reagents, ethyl (diarylphosphono)acetates 1, were prepared from triethyl phosphonoacetate, PCl5 the corresponding phenols. The reaction of 1 with several kinds of aldehydes in the presence of Triton B or NaH in THF solvent revealed that these reagents are useful for the synthesis of Z-unsaturated esters. Among the reagents examined, ethyl(di-o-tolylphosphono)-, [bis(o-ethylphenyl)phosphonol-, and [bis(o-isopropylphenyl)phosphono]acetates (1k-m) were found to be the most effective, giving Z-unsaturated esters with 93-99% selectivity.
- Ando, Kaori
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p. 1934 - 1939
(2007/10/03)
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- Diastereoselectivity of the conjugate addition of organocopper reagents to γ-alkoxy α,β-unsaturated carbonyl derivatives. Importance of the reagent type and the double-bond geometry
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Systematic investigations of the diastereoselectivity of organocopper conjugate addition to γ-alkoxy trans enoates (3), cis enoates (4), and diesters (5) revealed that the selectivity highly depended on the substrate structure and the reagent type. The an
- Yamamoto, Yoshinori,Chounan, Yukiyasu,Nishii, Shinji,Ibuka, Toshiro,Kitahara, Haruo
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p. 7652 - 7660
(2007/10/02)
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