Chiral palladium-pincer complex catalyzed asymmetric condensation of sulfonimines and isocyanoacetate

The asymmetric condensation of isocyanoacetate and sulfonimines was studied. Chiral BINOL and biphenantrol-based palladium-pincer complexes proved to be efficient catalysts affording 2-imidazoline derivatives with up to 86% ee. The level of enantioselectivity was clearly dependent on the γ-substituents of the BINOL ring. The best results were obtained by using biphenantrol-based pincer-complex catalysts. Some of the complexes induced the selective formation of the anti-diastereomer of the 2-imidazoline. The diastereo- and enantioselectivity showed an interesting solvent dependence as well. It was found that the application of diglyme as a solvent instead of THF leads to preferential formation of the anti product with a slight decrease of the enantioselectivity.

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(2S,3S) Methyl 2-formylamino-3-[(4-methylphenyl)sulfonyl] amino-3-phenylpropanoate[α]D20=+32 (c 1.1, THF); corresponds to a syn:anti ratio of 1.6:1 for which the enantiomeric excess was syn 86% and anti 28%Absolute configuration: (2S,3S)