Catalytic Synthesis of Peptide‐Derived Thiazolines and Oxazolines using Bis(quinolinolato)dioxomolybdenum(VI) Complexes

Bis(2‐ethyl‐8‐quinolinolato)dioxomolybdenum(VI) (9) (1 mol %) shows remarkable catalytic activity for the dehydrative cyclization of cysteine‐containing dipeptides 1 to give the corresponding thiazolines 2 with less than 6 % epimerization at the C2‐exomethine position. For the dehydrative cyclization of threonine‐containing dipeptides 4, 1 mol % of bis(2‐phenyl‐8‐quinolinolato)dioxomolybdenum(VI) (10) gives the corresponding oxazolines 5 with retention of configuration at the 5‐position.