Cinchona alkaloids: the structure of β-isocinchonicine revisited

Unexpected Inversions in Asymmetric Reactions: Reactions with Chiral Metal Complexes, Chiral Organocatalysts, and Heterogeneous Chiral Catalysts

“…On the basis of our experimental data and on the verified open-3 conformation of β-ICN , as well as on the widely accepted adsorption model, ,,,,, the proposed structure of the ICs responsible for the enantioselectivity is outlined in Figure . The formation of such nucleophilic complexes has been verified by NMR measurements in the liquid phase .…”

Asymmetric Catalysis at Chiral Metal Surfaces

“…275 The inversion induced by replacing CN with -isocinchonine 265 does not belong here since the latter compound represents a new modifier with an additional stereogenic center. 529 In many cases, the enantioselectivities are low and interpretation of the inversion is barely possible due to the corresponding small energy difference. The examples discussed below in more detail elucidate some aspects of the reaction mechanisms.…”

“…The observed inversions may be classified according to the parameter varied: (i) solvent composition, including variations in polarity ,,,, and addition of an acid ,,, or water; (ii) modifier concentration; ,,, (iii) temperature of catalyst modification (Ni−glutamic acid system); (iv) catalyst support (C or Al 2 O 3 ); (v) cleaning of the continuous reactor (removal of the soluble fraction of the modifier); (vi) size of the ester group in the substrate (Me or Et ester); (vii) reaction time (probably induced by transformation of the modifier during reaction); , and (viii) structure of the modifier while preserving the stereogenic centers, including protection of the OH function of CD by methyl 177,258,259,291,344 or other bulkier groups ,,,,,,, and protection of both N and OH functions . The inversion induced by replacing CN with β-isocinchonine 265 does not belong here since the latter compound represents a new modifier with an additional stereogenic center …”

Investigation of chiral reactions: the structural detection of new hydrogenated isocinchona alkaloids from mixtures without isolation using electrospray ionization tandem mass spectrometry

“…The possibilities of the formation of compound XI were discussed in an earlier publication 36. Production of XII – XIV can be interpreted by isomerization of the parent cinchona alkaloids under acidic conditions, a process recognized by Pasteur38 and later confirmed by other authors 39–42. The fragmentation of XI is shown in Fig.…”