An enantioselective formal synthesis of the proteasome inhibitor (+)-lactacystin

An enantioselective formal synthesis of the proteasome inhibitor (+)-lactacystin has been achieved using an alkylidene carbene 1,5-CH insertion reaction as a key step. The key cyclisation precursor was synthesised in high diastereomeric excess using a combination of known procedures, with the two key asymmetric centres being introduced via a Sharpless asymmetric epoxidation reaction. KHMDS induced 1,5-CH insertion produced a 3-pyrroline product, which was oxidised to the corresponding 3-pyrrolin-2-one using (1) TPAP/NMO; (2) NaClO2; (3) NaBH4. The formal synthesis was then completed with a few standard functional group interconversions.