We report the syn-selective Michael addition of a series of substituted primary and secondary nitromethane derivatives 4a-g to chiral enoates (Z)-2a and (E)-2a in the presence of TBAF‚3H 2 O or DBU. Regardless of the base employed, adducts syn-5a-g were obtained in good de (80-100%) from the reactions of 4a-g with (Z)-2a. However, in the addition to (E)-2a, the syn-diastereoselectivities depended on the structure of the nucleophile (80-90% de for nitromethane (4a), 80% de for phenylnitromethane (4g), 50 and 34% de for the primary nitromethane derivatives 4b and 4d, and 0 and 6% de for the secondary nitromethane derivatives 4c and 4f). A mixture of epimers (2:1/1:1) was obtained at the chiral center bearing the nitro group in 5b and 5d-g. The syn/anti ratio C-3,C-4 is kinetically controlled, while the epimeric ratio at the CNO 2 chiral center (C-1′) seems to be thermodynamically controlled. Adducts 5a,b,c,g were transformed into the respective cis-,γ-disubstituted γ-butyrolactones 6a, 7, 9a, and 9c. A mechanistic rationale to explain the observed diastereoselectivities is proposed.
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Syn-Selective Michael Addition of Nitromethane Derivatives toEnoates Derived from (R)-(+)-Glyceraldehyde Acetonide.-Chiral (Z)-and (E)-acetonides (I) and (IV) are added as Michael acceptors to nucleophilic nitro derivatives (II) and (V) in the presence of Bu4NF or DBU with syn-diastereoselectivity. Whereas the (Z) -isomer (I) gives independently of the type of nitro derivative good d. e. values, the syn-selectivity of (E)-isomer (IV) depends on the structure of the nucleophile. It is found that the syn/anti ratio is kinetically controlled, while the epimeric ratio at the C-NO2 chiral center seems to be thermodynamically controlled. -(COSTA, J. S.; DIAS, A. G.; ANHOLETO, A. L.; MONTEIRO, M. D.; PATROCINIO, V. L.; COSTA, P. R. R.; J.
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