cases with excellent diastereoselectivities and good to excellent enantioselectivities. A new synthetic strategy for the asymmetric synthesis of five-membered spiropyrazolones via N-heterocyclic carbene-catalyzed [3+2] annulations employing enals and unsaturated pyrazolones as substrates has been developed. The new protocol allows the flexible variation of all four substituents of the pharmaceutically
Lewis acid catalyzed annulation of spirocyclic donor–acceptor cyclopropanes with <i>exo</i>-heterocyclic olefins: access to highly functionalized bis-spirocyclopentane oxindole frameworks
作者:Kuldeep Singh、Sourav Pramanik、Trevor A. Hamlin、Biplab Mondal、Dinabandhu Das、Jaideep Saha
DOI:10.1039/c9cc03393a
日期:——
Lewisacidcatalyzedhighly efficient [3+2] annulation of spirocyclic Donor–Acceptorcyclopropanes (DACs) with exo-heterocyclic olefins is reported to furnish various biologically relevant dispiro-2,3-dioxopyrrolidine[cyclopentane]oxindole and dispiropyrazolone[cyclopentane]oxindole frameworks. This report highlights the use of oxindole-activated spiro-DACs as potential synthons to access complex dispirocarbocyclic
作者:Madavi S. Prasad、Murugesan Sivaprakash、A. Palanichamy
DOI:10.1039/d2ob01085b
日期:——
For the first time, [4 + 2]-annulation of in situ generated trienamine from 2-(E)-benzylidine-3-pyrrolidinyl acraldehyde with pyrazolone olefins has been developed to give hexahydrospiroindole pyrazolones with high chemo- and stereoselectivity.
AbstractDrug‐like spirocyclic scaffolds have been prepared asymmetrically by fusing fully functionalized cyclohexanes with medicinally important pyrazolone, rhodanine, barbituric acid or indandione moieties. This approach utilizes an organocatalytic tandem Michael–Michael–aldol reaction that yields diverse chiral spirocyclic backbones containing six contiguous stereogenic centers and multiple functional groups. The target compounds are generated in good yield and with high stereoselectivity (up to 99 % ee and 95:5 dr). Intriguingly, diastereocontrol of the spiro‐products changes depending on the substrate.magnified image
Knorr, Justus Liebigs Annalen der Chemie, 1887, vol. 238, p. 183