Radical versus Non-Radical Reactivity in ortho- and para-Quinonedimethides and Implications for Cycloaddition Mechanisms

Zhipeng Pei; Kieran P.E. Connor; Nicholas L. Magann; Michael G. Gardiner; Michelle L. Coote; Michael S. Sherburn

doi:10.1021/acs.orglett.4c03001

Radical versus Non-Radical Reactivity in ortho- and para-Quinonedimethides and Implications for Cycloaddition Mechanisms

Zhipeng Pei, Kieran P.E. Connor, Nicholas L. Magann, Michael G. Gardiner, Michelle L. Coote^*, Michael S. Sherburn^*

^*Corresponding author for this work

Research School of Chemistry

Research output: Contribution to journal › Article › peer-review

1 Citation (Scopus)

Abstract

The latent singlet diradical character of the parent ortho-quinonedimethide (o-QDM), as revealed by valence bond calculations, is demonstrated experimentally by trapping with the kinetically stable free radical TEMPO at room temperature. In the absence of TEMPO, the main pathway for decomposition at ambient temperature is not (as previously proposed in the literature) a radical reaction but instead a concerted Diels-Alder dimerization, which through ωB97X-D/aug-cc-pVTZ/SMD//M06-2X-D3/6-31+G(d,p)/SMD calculations is shown to proceed through an ambimodal bispericyclic transition state. The predominantly non-radical reactivity of o-QDM at room temperature differs from that of its isomeric para-quinonedimethide (p-QDM) congener, which self-reacts exclusively through radical pathways. These findings suggest the potential for tunable concerted/stepwise cycloadditions.

Original language	English
Pages (from-to)	8110-8114
Number of pages	5
Journal	Organic Letters
Volume	26
Issue number	38
DOIs	https://doi.org/10.1021/acs.orglett.4c03001
Publication status	Published - 27 Sept 2024

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title = "Radical versus Non-Radical Reactivity in ortho- and para-Quinonedimethides and Implications for Cycloaddition Mechanisms",

abstract = "The latent singlet diradical character of the parent ortho-quinonedimethide (o-QDM), as revealed by valence bond calculations, is demonstrated experimentally by trapping with the kinetically stable free radical TEMPO at room temperature. In the absence of TEMPO, the main pathway for decomposition at ambient temperature is not (as previously proposed in the literature) a radical reaction but instead a concerted Diels-Alder dimerization, which through ωB97X-D/aug-cc-pVTZ/SMD//M06-2X-D3/6-31+G(d,p)/SMD calculations is shown to proceed through an ambimodal bispericyclic transition state. The predominantly non-radical reactivity of o-QDM at room temperature differs from that of its isomeric para-quinonedimethide (p-QDM) congener, which self-reacts exclusively through radical pathways. These findings suggest the potential for tunable concerted/stepwise cycloadditions.",

author = "Zhipeng Pei and Connor, {Kieran P.E.} and Magann, {Nicholas L.} and Gardiner, {Michael G.} and Coote, {Michelle L.} and Sherburn, {Michael S.}",

note = "Publisher Copyright: {\textcopyright} 2024 American Chemical Society.",

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doi = "10.1021/acs.orglett.4c03001",

language = "English",

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T1 - Radical versus Non-Radical Reactivity in ortho- and para-Quinonedimethides and Implications for Cycloaddition Mechanisms

AU - Pei, Zhipeng

AU - Connor, Kieran P.E.

AU - Magann, Nicholas L.

AU - Gardiner, Michael G.

AU - Coote, Michelle L.

AU - Sherburn, Michael S.

PY - 2024/9/27

Y1 - 2024/9/27

N2 - The latent singlet diradical character of the parent ortho-quinonedimethide (o-QDM), as revealed by valence bond calculations, is demonstrated experimentally by trapping with the kinetically stable free radical TEMPO at room temperature. In the absence of TEMPO, the main pathway for decomposition at ambient temperature is not (as previously proposed in the literature) a radical reaction but instead a concerted Diels-Alder dimerization, which through ωB97X-D/aug-cc-pVTZ/SMD//M06-2X-D3/6-31+G(d,p)/SMD calculations is shown to proceed through an ambimodal bispericyclic transition state. The predominantly non-radical reactivity of o-QDM at room temperature differs from that of its isomeric para-quinonedimethide (p-QDM) congener, which self-reacts exclusively through radical pathways. These findings suggest the potential for tunable concerted/stepwise cycloadditions.

AB - The latent singlet diradical character of the parent ortho-quinonedimethide (o-QDM), as revealed by valence bond calculations, is demonstrated experimentally by trapping with the kinetically stable free radical TEMPO at room temperature. In the absence of TEMPO, the main pathway for decomposition at ambient temperature is not (as previously proposed in the literature) a radical reaction but instead a concerted Diels-Alder dimerization, which through ωB97X-D/aug-cc-pVTZ/SMD//M06-2X-D3/6-31+G(d,p)/SMD calculations is shown to proceed through an ambimodal bispericyclic transition state. The predominantly non-radical reactivity of o-QDM at room temperature differs from that of its isomeric para-quinonedimethide (p-QDM) congener, which self-reacts exclusively through radical pathways. These findings suggest the potential for tunable concerted/stepwise cycloadditions.

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DO - 10.1021/acs.orglett.4c03001

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AN - SCOPUS:85204053044

SN - 1523-7060

VL - 26

SP - 8110

EP - 8114

JO - Organic Letters

JF - Organic Letters

IS - 38

ER -

Radical versus Non-Radical Reactivity in ortho- and para-Quinonedimethides and Implications for Cycloaddition Mechanisms

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