Planar chiral 5,11-disubstiuted dibenzo[a,e]cyclo-octatetraenes (dbCOTs) have been developed as the first useful chiral homologs to dbCOT-ligands for asymmetric applications. Methods enabling the preparation of such compounds on a gram-scale in enantiomerically pure form are described. Evaluated as ligands in rhodium(I)-catalyzed 1,4- and 1,2-arylation reactions, tertiary and quarternary stereogenic centers were formed with excellent yields and selectivities of up to >99 % ee. A catalytic asymmetric synthesis of a key cyclization precursor to (-)-penifulvin A highlights the system in an applied context.
An ew bis(salicylimine)l igand based on the Trç-ger's base scaffold was synthesized in racemic and enantiomerically pure form. Upon coordinationt oz inc(II) ions this ligand undergoes highly diastereoselective self-assembly into neutral dinuclear double-stranded helicates as proven by XRD analysisa nd via comparison of experimental ECD spectra with those simulated with quantum-chemicalm ethods. When the racemic ligand was used, self-assembly occurs under narcissistic self-sorting resulting in the formation of ar acemic pair of helicates as revealed by NMR spectroscopya nd XRD analysis.
Aryl iodides are superior coupling partners in crosscoupling reactions compared to the corresponding chlorides or bromides. Unfortunately, the iodides are much more expensive, if commercially available at all, than the other halides. Thus, it is often mandatory to transform the available bromides into the corresponding iodides. The copper-catalyzed aromatic Finkelstein reaction turned out to be the method of choice to prepare a number of highly functionalized iodo(het)aryls, including pyridines, 2,2′-bipyridines, and chiral compounds.
The chirality of 5,11‐disubstituted dibenzo[a,e]cyclooctatetraene ligands is represented by a two‐fold axis of symmetry in molecular monarch‐butterflies searching for flowers (metal centers). A flap of the butterfly wings will interconvert enantiomeric insects in the same way as dissymmetric cyclooctatetraenes racemize. The symmetry of the butterflies is broken both by the pattern of the wings and through a single antenna on each head. The latter represents the 5,11‐pattern of substitution that gives rise to exceptionally efficient asymmetric catalysis. More information can be found in the Communication by D. Strand et al. on page 2344.
Eleven different derivatives of Tröger's base were synthesized and successfully resolved by (recycling) HPLC on chiral stationary (S,S)-Whelk-O1 or CHIRALPAK IA phase on a (semi-) preparative scale or synthesized in enantiomerically pure form. The absolute configuration was determined by X-ray crystal structure analysis, comparison of the quantum chemically calculated circular dichroism spectra with the experimental spectra, or comparison of specific rotations with literature data.
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