Enantioselective sequential Michael addition/C-H olefination/Michael reaction for the efficient collective synthesis of clavine alkaloids

Abstract

Sequential reactions are important for the direct and convenient synthesis of complex molecules with multiple chiral centers. Here, we report an enantioselective sequential Michael addition/C–H olefination/Michael addition reaction for the asymmetric construction of chiral 2-aminotetralin derivatives bearing three stereogenic centers using readily accessible 2-aryl N-quinolyl acrylamide, nitromethane, and alkenyl iodide. This optimized process utilizes a quinine-based squaramide bifunctional organocatalyst in the enantioselective Michael addition of nitromethane to a conjugated amide. Subsequently, the N,N-bidentate amide-directed Pd-catalyzed C–H olefination of the 2-arylamide and intramolecular Michael addition of a conjugated ester generates tetralins with high enantioselectivities and good stereoselectivities and yields. To demonstrate the synthetic utility of this sequential reaction, the collective synthesis of various clavine alkaloids with different skeletons is accomplished from a common tricyclic intermediate that can be readily prepared using chiral 2-aminotetralins.