So near so SPA: Achiral dirhodium(II) carboxylates and chiral spiro phosphoric acids (SPA) cooperatively catalyzed asymmetric NH insertion reactions with high enantioselectivity, high yields, and fast reaction rates at low catalyst loading (see scheme; Boc=tert-butyloxycarbonyl, TPA=triphenylacetyl). Chiral spiro phosphoric acid assisted asymmetric proton transfer is proposed as the chiral induction step.
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