Efficient optimization procedures in chiral catalysis are usually linked to a straightforward strategy to access groups of structurally similar catalysts required for fine-tuning. The ease of building up such ligand libraries can be increased when the structure-modifying step (introduction of a substituent) is done at a later stage of the synthesis. This is demonstrated for the extended family of di- and tetranaphtho azepinium compounds, widely used as chiral phase transfer catalysts (PTC). Using 2,6-diiodo-4,5-dihydro-3H-dinaphtho[2,1-c:1,2-e]azepine and 4,8-diiodo-6,7-dihydro-5H-dibenzo[c,e]azepine, respectively, as key intermediates, 18 spiro-azepinium compounds were synthesized in a total yield of 25–42% over 6–7 steps from 1,1-binaphthyl-2,2-dicarboxylic acid or diphenic acid, respectively. The replacement of iodo groups with aryl substituents was performed as the last or the penultimate step of the synthesis.
CITATION STYLE
Tharamak, S., Knittl-Frank, C., Manaprasertsak, A., Pengsook, A., Suchy, L., Schuller, P., … Widhalm, M. (2018). Economy of catalyst synthesis—convenient access to libraries of Di- and tetranaphtho azepinium compounds. Molecules, 23(4). https://doi.org/10.3390/molecules23040750
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