Isomerization of Epoxides

Abstract

Epoxides are highly useful synthetic intermediates andt hey can be synthesized stereo-andr egioselectively.D ue to the strained three-membered ring, their synthetic utility is limited. In many cases, it would be better to transform epoxides to other stable functional groups which could be used further in the synthesis. This isomerization would offer an alternate pathway to utilize the synthetic potential of epoxides.D espite the potential of such isomerization reactions,t hey have not been widely explored by chemists.Inthis review,the methods to isomerize epoxides into stablef unctional groups such as alcohols, aldehydes, ketones as well as trans-epoxides,b oth stereo-and regioselectively,are discussed.1I ntroduction 2E poxides to Alcohols 3E poxides to Carbonyl Compounds 4E poxy Alochols to Carbonyl Compounds by the Semipinacol Rearrangement 5 cis-trans IsomerizationofE poxides 6C onclusion

Smart Molecular Nanosheets for Advanced Preparation of Biological Samples in Electron Cryo-Microscopy

“…The bands at 3200–3600 cm –1 (OH-stretching mode) and 2875 and 2940 cm –1 (sym/asym C–H stretching mode) as well as the band at 1140 cm –1 (C–O–C stretching mode) are characteristic for PG (black spectrum in Figure ). The small, but significant band at 1740 cm –1 is characteristic for PG layers grafted at higher temperature (∼140 °C, see SI p. S4 for details) and is typically assigned to epoxy groups rearranged to carbonyl groups (Meinwald rearrangement) . After the coupling of the NTA 4 cyclen units to the PG-layer, the intensity of this band increased (red spectrum in Figure ), because of the introduction of additional carboxylic acid and carboxylic ester groups .…”

“…38 The small, but significant band at 1740 cm −1 is characteristic for PG layers grafted at higher temperature (∼140 °C, see SI p. S4 for details) and is typically assigned to epoxy groups rearranged to carbonyl groups (Meinwald rearrangement). 39 After the coupling of the NTA 4 cyclen units to the PG-layer, the intensity of this band increased (red spectrum in Figure 2), because of the introduction of additional carboxylic acid and carboxylic ester groups. 40 Moreover, a new band appeared at 1645 cm −1 , which was caused by CO stretching vibrations of amide groups, further confirmed the effective attachment of the NTA derivative.…”

Boron Reagents and Catalysts for the Functionalization of Strained Heterocycles

“…Generally, BF 3 −Et 2 O activates epoxides through coordination to the oxygen, but its strong Lewis acidity may easily cause polymerization or rearrangement to carbonyl compounds by alkyl or hydride shift [15] . Also particular substituted aziridines undergo BF 3 ‐catalyzed rearrangement (aza‐pinacol rearrangement) to the corresponding imines, [16] or isomerize to allylic amines [17] .…”

“…At the same time, the functionalization of strained heterocycles such as epoxides and aziridines represents a fundamental manipulation in synthetic organic chemistry as these compounds can be easily prepared from simple and readily available starting materials [1] . Due to ring strain, the metal‐catalyzed or promoted reactivity of epoxides and aziridines is invariably accompanied by a ring‐opening reaction delivering functionalized alcohols and amines or isomerized products [2] . In this context, the use of oxygenophilic boron‐based catalyst or promoter (such as BF 3 −Et 2 O) to trigger the nucleophilic ring‐opening reaction of epoxides (or their rearrangement) has been and still remains a fundamental tenet of this chemistry [3] .…”

Synthesis, characterization, and cytotoxic evaluation of iron oxide nanoparticles functionalized with galactomannan

“…The band at 550 cm -1 confirms the presence of iron oxide; the absence of the OH bands at 3200-3500 cm -1 suggests that the OH groups on iron oxide have mostly reacted with epichlorohydrin or Gal. The band at 1755 cm -1 (for carbonyl functionalities) suggests that perhaps some of the epoxides have been rearranged to carbonyl functionalities [34,35]. The band at 2802 cm -1 and the small band at 1050 cm -1 indicates the presence of galactomannan that is attached to iron oxide or epichlorohydrin residues, but the absence of the OH band at 3340 cm -1 suggests that the amount of galactomannan is either relatively low and/or that the OH in galactomannan has mostly reacted with epichlorohydrin or iron oxide.…”