Intermediates in the Formation and Thermolysis of Peroxides from Oxidations with Singlet Oxygen

2014 ◽  
Vol 67 (3) ◽  
pp. 320 ◽  
Author(s):  
Werner Fudickar ◽  
Torsten Linker
Keyword(s):  
Singlet Oxygen ◽  
Theoretical Work ◽  
Ene Reaction ◽  
Experimental Findings ◽  
Zwitterionic Intermediate ◽  
Concerted Reaction

Herein we describe the recent mechanistic understandings of the singlet oxygen ene reaction to give hydroperoxides and the [4+2] cycloaddition affording endoperoxides. Both experimental findings and theoretical work conclude in the formation of intermediates structurally similar to perepoxides during the ene reaction. Such intermediates mainly control the regio- and stereoselectivities of this reaction class. For the [4+2] cycloaddition, both a synchronous concerted reaction (benzene, naphthalenes) and a stepwise reaction with a non-symmetric zwitterionic intermediate (larger acenes) have been found. The thermolysis of endoperoxides derived from acenes proceeds stepwise for anthracenes, but in a concerted manner for less stable adducts such as naphthalene.

scholarly journals Bypassing the Multi-reference Character of Singlet Molecular Oxygen. Part 2: Ene-reaction

2021 ◽  
Author(s):  
Kurt Mikkelsen ◽  
Malte Jespersen ◽  
Matthew Johnson ◽  
Solvejg Jørgensen ◽  
Emma Petersen-Sonn
Keyword(s):  
Singlet Oxygen ◽  
Molecular Oxygen ◽  
Theoretical Calculations ◽  
Singlet Molecular Oxygen ◽  
Ene Reaction ◽  
Calculated Rate ◽  
Trans Butene ◽  
Oxygen Addition ◽  
Concerted Reaction

Theoretical calculations involving singlet molecular oxygen (O2(1g)) are challeng- ing due to their inherent multi-reference character. We have tested the quality of re- stricted and unrestricted DFT geometries obtained for the reaction between singlet oxy- gen and a series of alkenes (propene, 2-methylpropene, trans-butene, 2-methylbutene and 2,3-dimethylbutene) which are able to follow the ene-reaction. The electronic en- ergy of the obtained geometries are rened using 3 dierent methods which account for the multi-reference character of singlet oxygen. The results show that the mechanism for the ene-reaction is qualitatively dierent when either one or two allylic-hydrogen groups are available for the reaction. When one allylic-hydrogen group is available the UDFT calculations predict a stepwise addition forming a biradical intermediate, while, the RDFT calculations predict a concerted reaction where both hydrogen abstrac- tion and oxygen addition occur simultaneously. When two allylic-hydrogen groups are available for the reaction then UDFT and RDFT predict the same reaction mechanism, namely that the reaction occurs as a stepwise addition without a stable intermediate between the two transition states. The calculated rate constants are in reasonable agreement with experimental data, except for trans-butene where the calculated rate constant is three orders of magnitude lower than the experimental one. In conclusion we nd that the simple bypassing scheme tested in this paper is a robust approach for calculations of reaction involving singlet oxygen in the limit that the transition state processes low multi-reference character. 2

Photooxygenation in polymer matrices: En route to highly active antimalarial peroxides

2005 ◽  
Vol 77 (6) ◽  
pp. 1059-1074 ◽  
Author(s):  
Axel G. Griesbeck ◽  
Tamer T. El-Idreesy ◽  
Anna Bartoschek
Keyword(s):  
Singlet Oxygen ◽  
Protoporphyrin Ix ◽  
Polymer Matrices ◽  
Allylic Alcohols ◽  
Ene Reaction ◽  
Highly Active ◽  
Determining Factors ◽  
Broad Variety ◽  
Covalently Linked

Photooxygenation involving the first excited singlet state of molecular oxygen is a versatile method for the generation of a multitude of oxy-functionalized target molecules often with high regio- and stereoselectivities. The efficiency of singlet-oxygen reactions is largely dependent on the nonradiative deactivation paths, mainly induced by the solvent and the substrate intrinsically. The intrinsic (physical) quenching properties as well as the selectivity-determining factors of the (chemical) quenching can be modified by adjusting the microenvironment of the reactive substrate. Tetraarylporphyrins or protoporphyrin IX were embedded in polystyrene (PS) beads and in polymer films or covalently linked into PS during emulsion polymerization. These polymer matrices are suitable for a broad variety of (solvent-free) photooxygenation reactions. One specific example discussed in detail is the ene reaction of singlet oxygen with chiral allylic alcohols yielding unsaturated β-hydroperoxy alcohols in (threo) diastereoselectivities, which depended on the polarity and hydrogen-bonding capacity of the polymer matrix. These products were applied for the synthesis of mono- and spirobicyclic 1,2,4-trioxanes, molecules that showed moderate to high antimalarial properties. Subsequent structure optimization resulted in in vitro activities that surpassed that of the naturally occurring sesquiterpene-peroxide artemisinin.

Regioselectivity of the Singlet Oxygen Ene Reaction (Schenck Reaction) with Vinylsilanes

1994 ◽  
Vol 59 (12) ◽  
pp. 3335-3340 ◽  
Author(s):  
Waldemar Adam ◽  
Markus J. Richter
Keyword(s):  
Singlet Oxygen ◽  
Ene Reaction

scholarly journals Multivalent weak interactions enhance selectivity of interparticle binding

2020 ◽  
Vol 117 (37) ◽  
pp. 22690-22697 ◽  
Author(s):  
M. R. W. Scheepers ◽  
L. J. van IJzendoorn ◽  
M. W. J. Prins
Keyword(s):  
Targeted Drug Delivery ◽  
Colloidal Particles ◽  
High Selectivity ◽  
Weak Interactions ◽  
Theoretical Work ◽  
Coated Particles ◽  
Receptor Interactions ◽  
Two Factors ◽  
Experimental Findings

Targeted drug delivery critically depends on the binding selectivity of cargo-transporting colloidal particles. Extensive theoretical work has shown that two factors are necessary to achieve high selectivity for a threshold receptor density: multivalency and weak interactions. Here, we study a model system of DNA-coated particles with multivalent and weak interactions that mimics ligand–receptor interactions between particles and cells. Using an optomagnetic cluster experiment, particle aggregation rates are measured as a function of ligand and receptor densities. The measured aggregation rates show that the binding becomes more selective for shorter DNA ligand–receptor pairs, proving that multivalent weak interactions lead to enhanced selectivity in interparticle binding. Simulations confirm the experimental findings and show the role of ligand–receptor dissociation in the selectivity of the weak multivalent binding.

ChemInform Abstract: STEREOCHEMISTRY OF THE SINGLET OXYGEN, ENE REACTION WITH OLEFINS

1974 ◽  
Vol 5 (4) ◽  
pp. no-no
Author(s):  
L. M. STEPHENSON ◽  
D. E. MCCLURE ◽  
P. K. SYSAK
Keyword(s):  
Singlet Oxygen ◽  
Ene Reaction
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