124237-53-2Relevant academic research and scientific papers
Design of Chiral NHC-Carboxylates as Potential Ligands for Pd-Catalyzed Enantioselective C?H Activation
Niggli, Nadja E.,Baudoin, Olivier
, (2021)
Despite numerous efforts, the synthesis of scalemic carbo- and heterocycles through Pd0-catalyzed C(sp3)?H activation employing chiral ancillary ligands or chiral bases is still limited. Inspired by the recently reported outstanding performance of IBiox-type NHC ligands and bifunctional ligands in similar transformations, a new class of bifunctional NHC-ligands bearing a pendant carboxylate group was designed. A library of 10 imidazolium-carboxylic acids was obtained in five to six steps from enantiopure l-tert-leucinol. In addition, four well-defined Pd(DMBPA)-NHC palladacycles were synthesized in good to excellent yields from the corresponding imidazolium precursors. These complexes were tested in a prototypical C(sp3)?H arylation reaction, and the most active one afforded the indoline product in low yield but significant enantioselectivity. These new bifunctional NHCs could find broader applications in catalytic enantioselective transformations occurring under milder conditions.
Synthesis of Benzoheptalene
Guspanova, Jana,Knecht, Roger,Lugana, Markus,Weymuth, Christophe,Hansen, Hans-Juergen
, p. 1375 - 1407 (2007/10/03)
Benzoheptalene has been synthesized by two different approaches.The first one follows a pathway to hexahydrobenzoheptalenone 19a that has been already described by Wenkert and Kim (Scheme 1).Indeed, 19a was obtained in a mixture with its double-bond-shifted isomer 19b.Reduction of this mixture to the corresponding secondary alcohols 26a/26b and elimination of H2O lead to a mixture of the tetrahydrobenzoheptalenes 23a-d (Scheme 7 and 8).Reaction of 23a-d with 2 equiv. of triphenylmethylium tetrafluoroborate in boiling CHCl3, followed by treatment with Me3N in CH2Cl2, generated directly 2, unfortunately in a mixture with PH3CH that could not be separated from 2 (Scheme 10 and 11).The second approach via dimethyl benzoheptalene-6,7-dicarboxylate (30) (Scheme 12) that was gradually transformed into the corresponding carbaldehydes 37 and 43 (Scheme 14) both of which, on treatment with the Wilkinson catalyst at 130 deg C in toluene, smoothly decarbonylated, finally gave pure 2 as an unstable orange, viscous oil.UV/VIS, NMR, and mass spectra of 2 are discussed in detail. (cf.Chapt. 3).
