RESUMO
Cinchona alkaloid squaramide can effectively catalyze the asymmetric Michael addition of α-aryl isocyanoacetates to ß-trifluoromethylated enones, affording the corresponding adducts with an adjacent chiral tertiary carbon center bearing a CF3 group and a quaternary carbon center in moderate to good yields along with excellent stereoselectivities. The adduct can be easily transformed into biologically attractive chiral ß-trifluoromethylated pyrroline carboxylate in high yield via an isocyano group hydrolysis/cyclization/dehydration cascade reaction by treating with acid. The one-pot enantioselective Michael addition/isocyano group hydrolysis/cyclization/dehydration sequential protocol has also been investigated.
RESUMO
A highly enantioselective Michael addition of 3-aryloxindole to vinyl bisphosphonate ester catalyzed by a cinchonidine derived thiourea catalyst has been investigated. The corresponding adducts, containing a chiral quaternary carbon center and geminal bisphosphonate ester fragment at the 3-position of the oxindole, were obtained in moderate to good yields (65-92%) and moderate to good enantioselectivities (up to 92% ee).