119770-88-6Relevant articles and documents
Selective conjugate addition of nitromethane to enoates derived from D-mannitol and L-tartaric acid
Pinto, Americo C.,Freitas, Cleide B.L.,Dias, Ayres G.,Pereira, Vera L.P.,Tinant, Bernard,Declercq, Jean-Paul,Costa, Paulo R.R.
, p. 1025 - 1031 (2007/10/03)
The conjugate addition of nitromethane to enoates prepared from D-(+)-mannitol, substituted at the α-position by a methyl or a benzyl group, was investigated. While excellent syn-selectivity (d.e. >90%) was obtained from α-benzyl enoates (used as a mixture of epimers, E/Z=1.8:1), for α-methyl enoates the selectivity depended on the stereochemistry of the double bond in the acceptor (d.e. >90% for the (Z)-enoate and 50% for the (E)-enoate). In all cases, a mixture of epimers was formed at the newly generated stereocenter at the α-position. The epimeric syn-adducts were transformed into the corresponding pure α,β,γ-trisubstituted γ-butyrolactones by cyclization in acid medium followed by epimerization of the stereocenter at the α-position in DBU/CH2Cl2. When enoates derived from L-tartaric acid were used as acceptors, syn-selective conjugate additions were also observed (d.e. >90% for the (Z)-isomer and 50% for the (E)-isomer). The configuration at the newly generated stereogenic centers were assigned based on X-ray analyses, 1H-1H coupling constants and NOE experiments in NMR spectroscopy.
