Development of the Juliá asymmetric epoxidation reaction. Part 2. Application of the oxidation to alkyl enones, enediones and unsaturated keto esters

Abstract

Polyleucine-based systems have been used to catalyse the asymmetric oxidation of a variety of alkyl enones 1–4, 9–14, an enynone 16 and a dienone 17 to afford the corresponding epoxides 5–8, 18–26 in good to excellent yield and optical purity. A range of enediones 30–32, 34 and one unsaturated keto ester 33 have also been epoxidised stereoselectivley to afford optically active epoxides 35–39. The epoxidations were carried out with basic peroxide as the oxidant; the polyleucine catalyst was prepared from leucine N-carboxyanhydride using 1,3-diaminopropane, water (employing a humidity cabinet) or a polystyrene immobilised amine as the intiator. Preliminary mass spectral data on material derived from L-leucine and 1,3-diaminopropane (DAP-PLL) suggest that the catalyst consists of material that contains 22 ± 10 leucine residues.