Diphenylprolinol Silyl Ether as Catalyst of an Asymmetric, Catalytic, and Direct Michael Reaction of Nitroalkanes with α,β-Unsaturated Aldehydes
作者:Hiroaki Gotoh、Hayato Ishikawa、Yujiro Hayashi
DOI:10.1021/ol702545z
日期:2007.12.1
A catalyticenantioselective direct conjugate addition of nitroalkanes to alpha,beta-unsaturated aldehydes using diphenylprolinolsilylether as an organocatalyst has been developed. Using this methodology as a key step, short syntheses of therapeutically useful compounds have also been accomplished.
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.
Asymmetric Michael Reaction of Acetaldehyde Catalyzed by Diphenylprolinol Silyl Ether
An aldehyde with a cyclohexa‐2,5‐dienyl group in the α‐position is introduced as a storable surrogate of highly reactive acetaldehyde. The cyclohexa‐2,5‐dienyl unit is compatible with an enantioselective Michael addition to nitroalkenes promoted by a Hayashi–Jørgensen catalyst and can be removed by a boron Lewis acid mediated C−C bond cleavage. The robust two‐step sequence does not require a large