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Thermal and sonochemical studies on the Diels-Alder cycloadditions of masked o-benzoquinones with furans: New insights into the reaction mechanism

Thermal and sonochemical studies on the Diels-Alder cycloadditions of masked o-benzoquinones with furans: New insights into the reaction mechanism
Thermal and sonochemical studies on the Diels-Alder cycloadditions of masked o-benzoquinones with furans: New insights into the reaction mechanism
What does a Diels-Alder cycloaddition look like? This question is here addressed in the case of the increasingly significant cycloadditions of masked o-benzoquinones (MOBs), which serve as versatile dienes for the construction of complex and functionalized structures. So first, what the mechanism is not: It is not (by and large) a classical, concerted [4 + 2] cycloaddition. Experimental evidence is now supported by sonochemical studies, which were instrumental in elucidating the pathway. Reactions with furans are accelerated and improved under sonication, even when conducted at - 10 degreesC. Variation of the acoustic energy, temperature, and solvent composition allows us to optimize the yields and provide insights into the mechanism. Ultrasound does not cause sonochemical switching, as an alternative radical pathway should be ruled out. Results are consistent with a polar mechanism as claimed recently in a theoretical study. Moreover, this also does justice to a series of seminal papers, largely ignored, that gave a clue to the crucial issue of furan regioselectivity based on a nucleophilic addition. Most effects caused by ultrasonic agitation are of mechanochemical nature and suggest the existence of a perfectly stirred reactor with enhanced mass transfer.
bond-forming reactions, organic-synthesis, stereoselective-synthesis, photochemical-reactions, cis-decalins, electrochemical oxidation, cyclo-additions, cation radicals, efficient route, cope reactions
0022-3263
7193-7203
Avalos, M.
d6c0ff76-2d77-4fe6-89b5-463404a42de0
Babiano, R.
d79f2a4d-a2e3-4f73-8e58-65eee2a9f88a
Cabello, N.
00644978-5eb6-40b3-a498-8dcbc8a969a5
Cintas, P.
d4420202-106c-4e8a-b903-5deef99e6a39
Hursthouse, M. B.
57a2ddf9-b1b3-4f38-bfe9-ef2f526388da
Jimenez, J. L.
ea472a9b-29e7-46c1-8eb8-13616abf5492
Light, M. E.
cf57314e-6856-491b-a8d2-2dffc452e161
Palacios, J. C.
51c8b47c-ec5d-49f7-ba86-f76039defccc
Avalos, M.
d6c0ff76-2d77-4fe6-89b5-463404a42de0
Babiano, R.
d79f2a4d-a2e3-4f73-8e58-65eee2a9f88a
Cabello, N.
00644978-5eb6-40b3-a498-8dcbc8a969a5
Cintas, P.
d4420202-106c-4e8a-b903-5deef99e6a39
Hursthouse, M. B.
57a2ddf9-b1b3-4f38-bfe9-ef2f526388da
Jimenez, J. L.
ea472a9b-29e7-46c1-8eb8-13616abf5492
Light, M. E.
cf57314e-6856-491b-a8d2-2dffc452e161
Palacios, J. C.
51c8b47c-ec5d-49f7-ba86-f76039defccc

Avalos, M., Babiano, R., Cabello, N., Cintas, P., Hursthouse, M. B., Jimenez, J. L., Light, M. E. and Palacios, J. C. (2003) Thermal and sonochemical studies on the Diels-Alder cycloadditions of masked o-benzoquinones with furans: New insights into the reaction mechanism. Journal of Organic Chemistry, 68 (19), 7193-7203. (doi:10.1021/jo0348322).

Record type: Article

Abstract

What does a Diels-Alder cycloaddition look like? This question is here addressed in the case of the increasingly significant cycloadditions of masked o-benzoquinones (MOBs), which serve as versatile dienes for the construction of complex and functionalized structures. So first, what the mechanism is not: It is not (by and large) a classical, concerted [4 + 2] cycloaddition. Experimental evidence is now supported by sonochemical studies, which were instrumental in elucidating the pathway. Reactions with furans are accelerated and improved under sonication, even when conducted at - 10 degreesC. Variation of the acoustic energy, temperature, and solvent composition allows us to optimize the yields and provide insights into the mechanism. Ultrasound does not cause sonochemical switching, as an alternative radical pathway should be ruled out. Results are consistent with a polar mechanism as claimed recently in a theoretical study. Moreover, this also does justice to a series of seminal papers, largely ignored, that gave a clue to the crucial issue of furan regioselectivity based on a nucleophilic addition. Most effects caused by ultrasonic agitation are of mechanochemical nature and suggest the existence of a perfectly stirred reactor with enhanced mass transfer.

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More information

Published date: 19 September 2003
Keywords: bond-forming reactions, organic-synthesis, stereoselective-synthesis, photochemical-reactions, cis-decalins, electrochemical oxidation, cyclo-additions, cation radicals, efficient route, cope reactions

Identifiers

Local EPrints ID: 19882
URI: http://eprints.soton.ac.uk/id/eprint/19882
ISSN: 0022-3263
PURE UUID: 6b1b63ff-9cf2-4d04-9669-5a545eef4471
ORCID for M. E. Light: ORCID iD orcid.org/0000-0002-0585-0843

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Date deposited: 20 Feb 2006
Last modified: 08 Jan 2022 02:49

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Contributors

Author: M. Avalos
Author: R. Babiano
Author: N. Cabello
Author: P. Cintas
Author: J. L. Jimenez
Author: M. E. Light ORCID iD
Author: J. C. Palacios

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