189758-63-2Relevant articles and documents
Syn-Selective Michael Addition of Nitromethane Derivatives to Enoates Derived from (R)-(+)-Glyceraldehyde Acetonide
Costa, Jeronimo S.,Dias, Ayres G.,Anholeto, Aline L.,Monteiro, M?nica D.,Patrocinio, Vera L.,Costa, Paulo R.R.
, p. 4002 - 4006 (1997)
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·3H2O 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-diastereo-selectivities 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 CNO2 chiral center (C-1′) seems to be thermodynamicaliy controlled. Adducts 5a,b,c,g were transformed into the respective cis-β,γ-disubstituted γ-butyrolactones 6a, 7, 9a, and 9c. A mechanistic rationale to explain the observed diastereoselectivities is proposed.
Stereoselective conjugate addition of benzyl phenylsulfonyl carbanions to enoates derived from D-mannitol
Ferreira, Andre R. G.,Vilela, Guilherme V. M. De A.,Amorim, Mauro B.,Perry, Katia P.,Da Silva, Antonio J. R.,Dias, Ayres G.,Costa, Paulo R. R.
, p. 4013 - 4018 (2007/10/03)
The conjugate addition of benzylic phenylsulfonyl carbanions (2a′-d′) to enoates derived from D-(+)-mannitol (E- or Z-1a-c) was studied using THF and THF/HMPA as solvent. Under kinetic conditions (-78 °C), enoate E-1a,b led to a mixture of syn-(R,S) and a
