An asymmetric synthesis of carbocyclic spiroindoline by sequential Michael reaction and [3 + 2]-cycloaddition is described. This protocol demonstrates excellent enantio- and diastereoselectivity with broad functional group tolerance. A diverse range of spiroindolines were prepared by this approach, and the products served as ideal substrates for C2 derivatization.
Cyclic amines such as 1,2,3,4-tetrahydroisoquinoline undergo regiodivergent annulation reactions with 4-nitrobutyraldehydes. These redox-neutral transformations enable the asymmetric synthesis of highly substituted polycydic ring systems in just two steps from commercial materials. The utility of this process is illustrated in a rapid synthesis of (-)-protoemetinol. Computational studies provide mechanistic insights and implicate the elimination of acetic acid from an ammonium nitronate intermediate as the rate-determining step.
Chiral cobalt(II)-salen-catalyzed Michael addition of amines to β-substituted nitroalkenes
Optically active cobalt(II) salen complexes were found to be effective Lewis acid catalysts for the enantioselective Michael addition of O-alkylhydroxylamines to nitroalkenes to afford the corresponding N-alkylhydroxyl-1,2-nitroamines in high yields and with good to high enantioselectivities. This study represents the first example of a transition-metal-catalyzed asymmetric Michael addition of amines to nitroalkenes. (C) 2014 Elsevier Ltd. All rights reserved.