title: Practical and highly selective sulfur ylide-mediated asymmetric epoxidations and aziridinations using a cheap and readily available chiral sulfide: extensive studies to map out scope, limitations, and rationalization of diastereo- and enantioselectivities.
abstract: The chiral sulfide, isothiocineole, has been synthesized in one step from elemental sulfur, γ-terpinene, and limonene in 61% yield. A mechanism involving radical intermediates for this reaction is proposed based on experimental evidence. The application of isothiocineole to the asymmetric epoxidation of aldehydes and the aziridination of imines is described. Excellent enantioselectivities and diastereoselectivities have been obtained over a wide range of aromatic, aliphatic, and α,β-unsaturated aldehydes using simple protocols. In aziridinations, excellent enantioselectivities and good diastereoselectivities were obtained for a wide range of imines. Mechanistic models have been put forward to rationalize the high selectivities observed, which should enable the sulfide to be used with confidence in synthesis. In epoxidations, the degree of reversibility in betaine formation dominates both the diastereoselectivity and the enantioselectivity. Appropriate tuning of reaction conditions based on understanding the reaction mechanism enables high selectivities to be obtained in most cases. In aziridinations, betaine formation is nonreversible with semistabilized ylides and diastereoselectivities are determined in the betaine forming step and are more variable as a result.
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close BS8 1TS, United Kingdom.
authors.forename: Ona
authors.initials: O
authors.lastname: Illa
authors.forename: Mariam
authors.initials: M
authors.lastname: Namutebi
authors.forename: Chandreyee
authors.initials: C
authors.lastname: Saha
authors.forename: Mehrnoosh
authors.initials: M
authors.lastname: Ostovar
authors.forename: C Chun
authors.initials: CC
authors.lastname: Chen
authors.forename: Mairi F
authors.initials: MF
authors.lastname: Haddow
authors.forename: Sophie
authors.initials: S
authors.lastname: Nocquet-Thibault
authors.forename: Matteo
authors.initials: M
authors.lastname: Lusi
authors.forename: Eoghan M
authors.initials: EM
authors.lastname: McGarrigle
authors.forename: Varinder K
authors.initials: VK
authors.lastname: Aggarwal