Chiral CpxRhIII-catalyzed enantioselective C–H annulation to access fused tricyclic sulfur-stereogenic and medium-sized aza-heterocycles

Abstract

We report herein a chiral Cp^xRh^III-catalyzed asymmetric sp² C–H bond activation/annulation reaction of free NH-sulfoximines with hypervalent iodonium ylides under external ligand-free conditions. Efficient kinetic resolution (KR) was observed for the reactions of racemic sulfoximines bearing an asymmetric S-aryl-S-alkyl moiety, which also delivered the expected fused tricyclic (S)-aza-heterocycles and the corresponding chiral (R)-NH-sulfoximines in mostly good yields and with excellent enantioselectivities. Using this catalytic protocol, structurally unprecedented 10-membered S-stereogenic benzothiazecines with good enantioselectivities could be achieved upon one-pot multi-step oxidation reactions. Mechanistically, an enantiodetermined C–H cleavage and the subsequent formation of a chiral five-membered rhodacycle intermediate were supposed through systematic deuterium (D) labelling studies.