Fig. 5: Mechanistic study about NHC-catalyzed esterification of AAs.
From: Stereoselective diversification of α-amino acids enabled by N-heterocyclic carbene catalysis
A Standard conditionsa for control experiment: A mixture of AAs 1a (0.05 mmol), alcohol 2a (0.075 mmol), NHC-3a (20 mol%), Cs2CO3 (0.05 mmol) and DIC (0.06 mmol) dissolved in DCM (0.05 M) was stirred at r.t. for 2–10 h. Isolated yields are presented. Chiral HPLC determined ee and de values, see Supplementary Fig. S2. bOxazolone Int-1a as starting material without DIC in the std. cond. A, see Supplementary Fig. S1. B Na-protecting group impact. cDirect synthesis of oxazolone under DIC. C α-chirality interconversion between (S)- and (R)-configurations.
