An official website of the United States government
Abstract Anodic olefin coupling reactions generate new bonds and ring skeletons through a net two electron process that reverses the polarity of a known, electron‐rich functional group. While much of the early work on the mechanism of these reactions focused on the initial oxidation and cyclization steps of the process, the second oxidation step also plays a central role in determining the success of the reaction. Evidence supporting this observation is presented, along with evidence that optimization of this second oxidation step is not enough to pull a poor cyclization to the desired product. Successful cyclization reactions require optimization of both processes.
more »
« less
Synthesis of Alkyl Aryl Ethers by O-Arylation of Alcohols with Diaryliodonium Salts: Scope, Limitations, and Mechanism
Abstract We describe the development of a C–O coupling reaction between aryl(2,4,6-trimethoxyphenyl)iodonium salts and aliphatic alcohols under weak base conditions. The scope of the reaction is presented, with 16 examples ranging in yield from moderate to high (54–96%). The limitations of the reaction are also presented. Mechanistic experiments reveal a complex network of reactions that include side reactions that generate arynes and oxidize the alcohol nucleophile.
more »
« less
- Award ID(s):
- 2154500
- PAR ID:
- 10536751
- Publisher / Repository:
- Thieme Medical Publisher, Georg Thieme Verlag KG
- Date Published:
- Journal Name:
- Synlett
- Volume:
- 35
- Issue:
- 08
- ISSN:
- 0936-5214
- Page Range / eLocation ID:
- 889 to 894
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract CreE is a flavin‐dependent monooxygenase (FMO) that catalyzes three sequential nitrogen oxidation reactions of L‐aspartate to produce nitrosuccinate, contributing to the biosynthesis of the antimicrobial and antiproliferative nautral product, cremeomycin. This compound contains a highly reactive diazo functional group for which the reaction of CreE is essential to its formation. Nitro and diazo functional groups can serve as potent electrophiles, important in some challenging nucleophilic addition reactions. Formation of these reactive groups positions CreE as a promising candidate for biomedical and synthetic applications. Here, we present the catalytic mechanism of CreE and the identification of active site residues critical to binding L‐aspartate, aiding in future enzyme engineering efforts. Steady‐state analysis demonstrated that CreE is very specific for NADPH over NADH and performs a highly coupled reaction with L‐aspartate. Analysis of the rapid‐reaction kinetics showed that flavin reduction is very fast, along with the formation of the oxygenating species, the C4a−hydroperoxyflavin. The slowest step observed was the dehydration of the flavin. Structural analysis and site‐directed mutagenesis implicated T65, R291, and R440 in the binding L‐aspartate. The data presented describes the catalytic mechanism and the active site architecture of this unique FMO.more » « less
-
Abstract Paired electrochemical reactions allow the optimization of both atom and energy economy of oxidation and reduction reactions. While many paired electrochemical reactions take advantage of perfectly matched reactions at the anode and cathode, this matching of substrates is not necessary. In constant current electrolysis, the potential at both electrodes adjusts to the substrates in solution. In principle, any oxidation reaction can be paired with any reduction reaction. Various oxidation reactions conducted on the anodic side of the electrolysis were paired with the generation and use of hydrogen gas at the cathode, showing the generality of the anodic process in a paired electrolysis and how the auxiliary reaction required for the oxidation could be used to generate a substrate for a non‐electrolysis reaction. This is combined with variations on the cathodic side of the electrolysis to complete the picture and illustrate how oxidation and reduction reactions can be combined.more » « less
-
Abstract Mechanical stress can directly activate chemical reactions by reducing the reaction energy barrier. A possible mechanism of such mechanochemical activation is structural deformation of the reactant species. However, the effect of deformation on the reaction energetics is unclear, especially, for shear stress-driven reactions. Here, we investigated shear stress-driven oligomerization reactions of cyclohexene on silica using a combination of reactive molecular dynamics simulations and ball-on-flat tribometer experiments. Both simulations and experiments captured an exponential increase in reaction yield with shear stress. Elemental analysis of ball-on-flat reaction products revealed the presence of oxygen in the polymers, a trend corroborated by the simulations, highlighting the critical role of surface oxygen atoms in oligomerization reactions. Structural analysis of the reacting molecules in simulations indicated the reactants were deformed just before a reaction occurred. Quantitative evidence of shear-induced deformation was established by comparing bond lengths in cyclohexene molecules in equilibrium and prior to reactions. Nudged elastic band calculations showed that the deformation had a small effect on the transition state energy but notably increased the reactant state energy, ultimately leading to a reduction in the energy barrier. Finally, a quantitative relationship was developed between molecular deformation and energy barrier reduction by mechanical stress.more » « less
-
Freeman, S.; Lederer-Woods, C.; Manna, A.; Mengoni, A. (Ed.)The formation of nuclei in slightly proton-rich regions of the neutrino-driven wind of core-collapse supernovae could be attributed to the neutrino-p process (νp-process). As it proceeds via a sequence of (p,γ) and (n,p) reactions, it may produce elements in the range of Ni and Sn, considering adequate conditions. Recent studies identify a number of decisive (n,p) reactions that control the efficiency of the νp-process. The study of one such (n,p) reaction via the measurement of the reverse (p,n) in inverse kinematics was performed with SECAR at NSCL/FRIB. Proton-induced reaction measurements, especially at the mass region of interest, are notably difficult since the recoils have nearly identical masses as the unreacted projectiles. Such measurements are feasible with the adequate separation level achieved with SECAR, and the in-coincidence neutron detection. Adjustments of the SECAR system for the first (p,n) reaction measurement included the development of new ion beam optics, and the installation of the neutron detection system. The aforementioned developments along with a discussion on the preliminary results of the p( 58 Fe,n) 58 Co reaction measurement are presented.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1055/a-2198-3637
