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Mechanism of the Os-catalyzed oxidative cyclization of 1,5-dienes

Mechanism of the Os-catalyzed oxidative cyclization of 1,5-dienes
Mechanism of the Os-catalyzed oxidative cyclization of 1,5-dienes
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/aug-cc-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.
0022-3263
Hussein, Aqeel
c6645ce9-c288-4b21-8af4-6f481b600bf1
Phipps, Maximillian
290febb8-7f0a-4bda-9944-96594d6343d2
Skylaris, Chris-Kriton
8f593d13-3ace-4558-ba08-04e48211af61
Brown, Richard C.D.
21ce697a-7c3a-480e-919f-429a3d8550f5
Hussein, Aqeel
c6645ce9-c288-4b21-8af4-6f481b600bf1
Phipps, Maximillian
290febb8-7f0a-4bda-9944-96594d6343d2
Skylaris, Chris-Kriton
8f593d13-3ace-4558-ba08-04e48211af61
Brown, Richard C.D.
21ce697a-7c3a-480e-919f-429a3d8550f5

Hussein, Aqeel, Phipps, Maximillian, Skylaris, Chris-Kriton and Brown, Richard C.D. (2019) Mechanism of the Os-catalyzed oxidative cyclization of 1,5-dienes. Journal of Organic Chemistry. (doi:10.1021/acs.joc.9b02174).

Record type: Article

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/aug-cc-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.

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jo-2019-02174b Accepted version - Accepted Manuscript
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Accepted/In Press date: 30 October 2019
Published date: 30 October 2019

Identifiers

Local EPrints ID: 435790
URI: http://eprints.soton.ac.uk/id/eprint/435790
ISSN: 0022-3263
PURE UUID: ae56fadc-fef6-4baf-860d-2de2089f8a5a
ORCID for Chris-Kriton Skylaris: ORCID iD orcid.org/0000-0003-0258-3433
ORCID for Richard C.D. Brown: ORCID iD orcid.org/0000-0003-0156-7087

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Date deposited: 20 Nov 2019 17:30
Last modified: 22 Nov 2021 07:49

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Author: Aqeel Hussein
Author: Maximillian Phipps

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