Transformation of Racemic Azlactones into Enantioenriched Dihydropyrroles and Lactones Enabled by Hydrogen‐Bond Organocatalysis

Abstract

Azlactones, a potent building block for the synthesis of complex molecules, have been explored in an organocatalytic Mannich reaction with protected imines. In this study, azlactones containing a propargyl substituent were employed for the first time in organocatalysis so far. The catalytically active species responsible for high enantioselectivity with substrate containing such a small linear substituent is assembled in situ from a bifunctional thiourea, prone to dimerization, and an organic acid, as evidenced by DOSY NMR. The resulting α,β‐diamino acid derivatives were subjected to further derivatization: as an example, gold‐catalyzed intramolecular hydroamination of alkynes gave chiral spirocyclic dihydropyrrole. Alternatively, related squaramide catalyst enabled a Mannich reaction of azlactones with N‐aryl or alkyl glyoxylate imines. Reduction of these adducts gave access to 2,3‐diaminobutyrolactones or 2,3‐diamino‐1,4‐diol with a tertiary and a quaternary stereocenter.