Mechanism of Os-Catalyzed Oxidative Cyclization of 1,5-Dienes

Abstract

The oxidative cyclization of 1,5-dienes by metal oxo species is a powerful method for stereocontrolled synthesis of tetrahydrofuran diols (THF-diols), structural motifs present in many bioactive natural products. Oxidative cyclization of (2E,6E)-octa-2,6-diene catalyzed by OsO4/NMO as has been studied using density functional theory (DFT) calculations (M06-2X/augcc-pVDZ/Hay-Wadt VDZ (n+1) ECP), highlighting the remarkable effect of acid on the fate of the first intermediate, an Os(VI) dioxoglycolate. Strong acid promotes cyclization of the Os(VI) dioxoglycolate, or its NMO complex, through protonation of an oxo ligand to give more electrophilic species. By contrast, in absence of acid reoxidation may occur to afford the Os(VIII) trioxoglycolate, which is shown to favor conventional "second cycle" dihydroxylation reactivity rather than cyclization. The results of the calculations are consistent with experimental results for reactions of OsO4/NMO with 1,5-dienes with acid (oxidative cyclization) and without acid (second cycle osmylation / dihydroxylation). Detailed evaluation of potential catalytic cycles support oxidation of the cyclized Os(IV) THF diolate intermediate to the corresponding Os(VI) species followed by slow hydrolysis, and finally regeneration of OsO4.

Elucidating the Mechanism of Tetrahydrofuran-Diol Formation through Os(VI)-Catalyzed Oxidative Cyclization of 5,6-Dihydroxyalkenes Ligated by Citric Acid

“…In 2010, a DFT study of the oxidative cyclization of 1,5-dienes by OsO 4 was reported by Poethig and Strassner, where the reaction pathway was built on two key steps: alkene osmylation and cyclization via Os­(VIII) glycolate intermediate to form the THF ring . However, Donohoe and co-workers showed that the cyclization is viable through a protonated Os­(VI) intermediate. , In 2019, our DFT study emphasized the remarkable impact of Bro̷nsted acid on the fate of cyclization through NMO-complexed Os­(VI) dioxoglycolate ( E , Figure b) . Our findings revealed a potential catalytic cycle wherein oxidation of the cyclized NMO-complexed Os­(IV) THF-diolate intermediate F to the corresponding Os­(VI) species G occurs, followed by slow hydrolysis and eventual regeneration of OsO 4 .…”

“…However, upon protonation and complexation, a low energy gap is obtained in agreement with the low barrier of cyclization being calculated for Int20 (9.9 kcal/mol via TS18 ) and Int24 (12.8 kcal/mol via TS14 ) (Figure ). The low barriers for oxo-protonated or alkoxy-protonated Os­(VI) intermediates Int20 and Int24 are clearly attributed to the decrease in LUMO orbitals, increasing the electrophilicity of the Os center …”

Capture and immobilization of gaseous ruthenium tetroxide RuO4 in the UiO-66-NH2 metal–organic framework

“…8). This type of reaction has been studied for OsO 4 53,54 or RuO 4 55 on simple aromatic systems or double bonds. DFT calculations confirmed the good affinity between the ditopic ligand of UiO-66-NH 2 and RuO 4 , through strong hydrogen bonding between the porous framework (from NH 2 groups connected to neighboring ligands) and the gaseous species in intermediate 1.…”

Mechanistic investigations on Pinnick oxidation: a density functional theory study

“…Secondly, proton transfer from chlorous acid represents the first-half pathway, from the pre-reaction complex until the TS, with a noticeable change of the bond length near TS. Due to significant differences between the progressions of the two bond formations O-H and C-O in the TS 8, it would be valuable to get more validations on PES towards the chronological formation of these bonds from the point of molecular dynamic (MD) simulations, especially the behaviour of the system within time (figure 8) (for the molecular dynamics on transition state structures see: [60][61][62][63][64][65][66]). Classical MD calculations were carried out on one trajectory, where the forward and backward propagation of TSs are initiated in the region of the PES near the TS (t = 0 fs) showing the typical reactive bonds toward intermediate 9 and reactants (acrylaldehyde and chlorous acid).…”

“…open sci. 7: 191568 structures see:[60][61][62][63][64][65][66]). Classical MD calculations were carried out on one trajectory, where the forward and backward propagation of TSs are initiated in the region of the PES near the TS (t = 0 fs) showing the typical reactive bonds toward intermediate 9 and reactants (acrylaldehyde and chlorous acid).…”