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

Multicomponent synthesis of new bis(pyranpyrazole) and their antimicrobial-antioxidant evaluations

One-pot, three-component reactions were utilized to obtain a series of new symmetrical bis(pyranopyrazoles) built around six rigid linkers in good yields and in the short durations under normal conditions. The structures of the prepared compounds were confirmed using their IR, 1H-NMR, 13C-NMR and ESI-MS spectral parameters. The bis(pyranopyrazoles) 3b and 3f exhibited significant antimicrobial action against Klebsiella pneumoniae, Fusarium oxysporum and Penicillium glabrum at a minimum inhibitory concentration (MIC) value of 3.12 ?g mL-1, which is equivalent to the MIC of the standard drug. trans-Butene-linked bis(pyranopyrazole) 3f was also associated with a good radical scavenging activity similar to that of ascorbic acid (a standard antioxidant).