Total Synthesis with a Chirogenic Opening Move Demonstrated on Steroids with Estrane or 18a-Homoestrane Skeleton
作者:Gerhard Quinkert、Michael Del Grosso、Astrid Döring、Wolfgang Döring、Ralf I. Schenkel、Markus Bauch、Gernot T. Dambacher、Jan W. Bats、Gottfried Zimmermann、Gerd Dürner
DOI:10.1002/hlca.19950780524
日期:1995.8.9
A concept of first choice for the synthesis of the title compounds had been proposed by Dane in the late 1930s. It was soon turned down, because the opening move–a chirogenic Diels-Alder reaction – did not work. With Lewis acids as mediators, however, a successful start has been achieved now. With Ti complexes of chelating ligands (Seebach's TADDOLs (= α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanols))
Catalysis of a Diels−Alder Reaction by Amidinium Ions
作者:Tilmann Schuster、Markus Kurz、Michael W. Göbel
DOI:10.1021/jo991372x
日期:2000.3.1
lipophilic amidinium ions catalyze a cycloaddition reaction representing the keystep of the Quinkert-Daneestronesynthesis. Hydrogen-bond-mediated association with the organic cation leads to an electrophilic activation of the dienophile and to enhanced rates of the Diels-Alderreaction. The observed effects are similar to those expected from mild Lewis acids. In competition experiments, amidinium catalysis
A C2-Chiral Bis(amidinium) Catalyst for a Diels−Alder Reaction Constituting the Key Step of the Quinkert−Dane Estrone Synthesis
作者:Svetlana B. Tsogoeva、Gerd Dürner、Michael Bolte、Michael W. Göbel
DOI:10.1002/ejoc.200200635
日期:2003.5
A novel C2-chiralbis(amidinium) salt 12 has been synthesised from 5-(tert-butyl)isophthalic acid. The hydrogen-bond-mediated association of dienophiles 3a and 3b with the chiral host molecule 12 accelerates the Diels−Alderreactions with diene 2 by more than three orders of magnitude. In addition, enantioselective formation of the desired adducts is observed under catalysis with 12. Good ratios of