Epoxidation of alkenes by dimethyldioxirane: Evidence for a spiro transition state

Effect of α-fluorination on asymmetric epoxidation of trans-olefins using α-fluorinated cyclohexanone dioxiranes

“…The stereochemical outcomes of epoxidations of transstilbene with ketones 3a-5a (leading to (À)-(S, S) stilbene oxide) and p-methoxy cinnamate with ketones 3a and 4a (leading to (À)-(2R, 3S) cinnamate oxide) have already been rationalized [7,9] by considering the model shown on Scheme 4: conformation K1 of the dioxirane (predicted to be the most populated because of the large i-Pr group equatorial); spiro geometry; [19][20][21][22] equatorial approaches of the olefin toward the dioxirane (with some contribution of the axial approaches, although less favored [9]) and n(F).p(Ar) or n(F).CH 3 repulsion in approach E-I (making the corresponding transition state more energetic than the one corresponding to approach E-II).…”

VCD configuration of enantiopure/‐enriched tetrasubstituted α‐fluoro cyclohexanones and their use for epoxidation of trans‐olefins

“…), dissolved in 6 mL in distilled water, was added using a syringe pump to the reaction mixture for 6 h. A 1M K 2 CO 3 solution was added dropwise to maintain the pH at f9.5. Conversions were deter-mined on the 1 H NMR 400 MHz spectra (CDCl 3 ) of the crude products of the reactions and the enantiomeric ratios were determined by 1 H NMR 400 MHz (CDCl 3 ) using Eu(hfc) 3 as chiral shift reagent. The absolute configuration of the epoxides was determined through the sign of the optical rotation and comparison with literature data.…”

Kinetics of the Epoxidation of Geraniol and Model Systems by Dimethyldioxirane

“…Geraniol (1), 2-methyl-2-pentene (5), 3-methyl-2-buten-1-ol (6) and Oxone® (2HKSO 5 •HKSO 4 •K 2 SO 4 ) were obtained commercially (Aldrich) and were used without further purification. Isolated dried dioxirane 1 (0.1 M, in acetone) was prepared by a procedure [4] that was an adaptation of the experimental approach of Murray and Jeyaraman [3a]. Also see W. Adam et al [3d].…”

“…Dimethyldioxirane (1), either generated in situ [2] or in isolated solution [3], has been found to be a versatile epoxidizing reagent for a wide variety of alkenes. Epoxidation by 1 has been shown to be stereospecific and quantitative and to occur via a concerted electrophilic process with a "spiro" transition state [4]. The reaction of alkenes with 1 has been shown to be sensitive to steric factors.…”

“…The reaction of alkenes with 1 has been shown to be sensitive to steric factors. In general, cis alkenes have been found [4] to show greater reactivity than the corresponding trans compounds. Recently, product studies on the epoxidation of alkenes containing hydroxy groups have suggested [5,6] that (intermolecular) hydrogen bonding increases reactivity and affects product distributions.…”