Copper-Catalyzed Annulation/A3-Coupling Cascade: Diastereodivergent Synthesis of Sterically Hindered Monocyclic Oxazolidines Bearing Multiple Stereocenters

The Cu-catalyzed synthesis of densely functionalized chiral oxazolidines with three stereogenic centers via an annulation/A3-coupling cascade is described using chiral 1,2-amino alcohol precursors. The solvent-free synthetic approach tolerates an extremely broad substrate scope of the starting compounds (aldehydes, and alkynes), and provides the sterically hindered target monocyclic molecules with good yields and excellent diastereomeric ratio. Moreover, changing the alkyne to a propiolic acid is demonstrated here to be useful, and the corresponding titled products can be employed as a convenient building block for the preparation of 1,4-diamino-2-butynes via one-pot, two-step sequential reaction.