Synthetic study demonstrates Ullmann coupling yields atropisomerically stable binaphthyls for asymmetric catalysis, highlighting novel chiral ligands.
Axially chiral binaphthyls 3a and 3b were synthesized taking, advantage of Ullman coupling of 4a and 4b, respectively. The binaphthyls were shown to be stable to atropisomerization. Binaphthol 3b was resolved with (−)-(1 S )-menthyl chloroformate ( 11 ). R -axis diastereomer of bisoxazoline 3b was used for enantioselective cyclopropanation of styrene with ethyl diazoacetate.
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Kolotuchin et al. (1999) studied this question.
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