RESUMEN
A range of nitroalkenes 1 and imines 3 derived from alkyl, aryl, and heteroaryl aldehydes underwent a tandem 1,4-hydride addition nitro-Mannich reaction to afford anti-rich ß-nitroamines 4. The crude anti-ß-nitroamines 4 could be converted to the corresponding anti-ß-nitroacetamides 5 (33 examples) to allow purification in good yield from the parent nitroalkenes (60-87%), and with a high diastereomeric ratio (90:10 to mostly >95:5). A representative selection of anti-ß-nitroacetamides 5 (five examples) were reduced to vicinal diamines 7 with zinc hydrochloride; concomitant acyl migration provided differentially protected vicinal diamines 7 in good yield (80-91%).
RESUMEN
Copper-catalyzed conjugate addition of diorgano zinc reagents to nitroacrylate 1 followed by a subsequent nitro-Mannich reaction and in situ lactamization leads to an efficient one-pot synthesis of 1,3,5-trisubstituted 4-nitropyrrolidin-2-ones (5). The versatility of the reaction is shown for a wide range of N-p-(methoxy)phenyl protected aldimines 3 derived from alkyl, aryl, and heteroaryl aldehydes. The densely functionalized pyrrolidin-2-ones 5 are isolated as single diastereoisomers (40 examples, 33-84% yield). An enantioselective copper-catalyzed conjugate addition of diethylzinc led to highly crystalline products that could be recrystallized to enantiopurity in high yield. A range of successful chemoselective transformations were investigated, which widens the applicability of the pyrrolidn-2-ones as stereochemically pure building blocks for further organic synthesis.
Asunto(s)
Pirrolidinonas/síntesis química , Catálisis , Cobre/química , Estructura Molecular , Nitrocompuestos/química , Compuestos Organometálicos/química , Pirrolidinonas/química , Estereoisomerismo , Zinc/químicaRESUMEN
We report an enantioselective conjugate addition nitro-Mannich reaction protocol which combines dialkylzinc, aromatic nitro alkene and imine to form two C-C bonds and three contiguous stereocenters in one reaction vessel. Absolute stereochemistry was controlled from the initial 1,4-addition of dialkylzinc to aromatic nitroalkenes by known copper-chiral ligand catalysts. The choice of solvent dictated the formation of either the syn,anti or syn,syn diastereoisomers, two of the four possible diastereoisomers. The syn,syn isomer is a rare example of a syn-selective nitro-Mannich reaction. The diastereoselectivity is dependent upon the presence or not of Zn(O(2)CCF(3))(2) in the reaction mixture and empirical transition state models are proposed to account for the observed stereochemical course of the two reaction conditions. The extent of enantioselectivity and structural diversity of the process is limited by current methodology for the catalytic asymmetric addition of dialkylzincs to nitrostyrenes. The synthetically versatile products are the most complex ß-nitro amines prepared using the nitro-Mannich reaction and are formed in high yield and enantioselectivity.