E. Licandro et al., Michael addition of chiral Fischer aminocarbene complexes to nitroolefins:Study on the effect of the Michael acceptor structure on diastereoselectivity, ORGANOMETAL, 20(3), 2001, pp. 485-496
The anions of the pentacarbonyl(chromium) trans-2,6-dimethylmorpholinyl(met
hyl)carbene and pentacarbonyl(chromium) trans-3,5-dimethylpiperidinyl(methy
l)carbene complexes added to E- and Z-nitrostyrenes through a diastereosele
ctive Michael-type reaction to give precursors of beta -aryl-gamma -butyric
acid derivatives. The diastereoselectivity observed with the former carben
e was dependent on the nature of the substituent present in the 4-position
of nitrostyrenes and was higher when it was an electron-withdrawing group.
The presence of 12-crown-4 ether in the reaction medium increased both reac
tion times and diastereoselectivity. Theoretical calculations were performe
d to rationalize the stereochemical outcomes of the reactions and to suppor
t the proposed transition state models.