Stereoselective additions of chiral .alpha.-sulfinyl ketimine anions to ene esters. Asymmetric syntheses of indolo[2,3-a]quinolizidine and yohimban alkaloids
摘要:
The in-situ 1,4-addition/ring-closure reactions of chiral alpha-sulfinyl ketimine anions with acyclic and cyclic ene esters offer a simple, convenient route for the construction of chiral cyclic alkaloids having a nitrogen-atom ring juncture. Asymmetric induction in the conjugate-addition reaction of the carbanions derived from alpha-sulfinyl ketimines possessing chiral sulfur with various cyclic and acyclic ene esters, subsequent ring-closure reaction, and reduction of the resulting beta-sulfinyl enamides were utilized in the syntheses of (-)-1,2,3,4,6,7,12,12b-octahydroindolo[2,3-a] quinolizine [(-)-1], (-)-alloyohimban [(-)-2], (+)-3-epi-alloyohimban [(+)-3], and (-)-yohimban [(-)-4].
PCET-Enabled Olefin Hydroamidation Reactions with <i>N</i>-Alkyl Amides
作者:Suong T. Nguyen、Qilei Zhu、Robert R. Knowles
DOI:10.1021/acscatal.9b00966
日期:2019.5.3
Olefin aminations are important synthetic technologies for the construction of aliphatic C-N bonds. Here we report a catalytic protocol for olefin hydroamidation that proceeds through transient amidyl radical intermediates that are formed via proton-coupled electron transfer (PCET) activation of the strong N-H bonds in N-alkyl amides by an excited-state iridium photocatalyst and a dialkyl phosphate