The University of Southampton
University of Southampton Institutional Repository

Dissecting competitive mechanisms: thionation vs. cycloaddition in the reaction of thioisomu?nchnones with isothiocyanates under microwave irradiation

Dissecting competitive mechanisms: thionation vs. cycloaddition in the reaction of thioisomu?nchnones with isothiocyanates under microwave irradiation
Dissecting competitive mechanisms: thionation vs. cycloaddition in the reaction of thioisomu?nchnones with isothiocyanates under microwave irradiation
This paper documents in detail the reaction of 1,3-thiazolium-4-olates (thioisomnchnones) with aryl isothiocyanates. Having demonstrated with a chiral model that thionation occurs under these conditions to provide 1,3-thiazolium-4-thiolates and that this process is actually a stepwise domino reaction (J. Org. Chem. 2009, 74, 3698?3705), we extend this study to monocyclic thioisomnchnones. Herein, competition between thionation and 1,3-dipolar cycloaddition takes place. The process is synthetically disappointing at room temperature requiring prolonged reaction times for completion. The protocol has been subsequently investigated by using both microwave dielectric heating and conventional thermal heating (oil bath) in DMF at 100 °C with an accurate internal reaction temperature measurement. Although a slight acceleration was observed for reactions conducted under microwave irradiation, for most cases the observed yields and chemoselectivities were quite similar. Thus one can conclude that, within experimental errors, the reactivity is not related to nonthermal effects in agreement with recent reassessments on this subject, particularly by Kappe and associates (J. Org. Chem. 2008, 73, 36; J. Org. Chem. 2009, 74, 6157). The whole reaction system, which includes numerous heavy atoms, can be computationally modeled with a hybrid ONIOM[B3LYP/6-31G(d):PM3] level. This reproduces well experimental results and suggests a sequential mechanism. To further corroborate the nonconcertedness, the potential energy surface (PES) has been constructed for simplified models, locating the corresponding stationary points. In doing so, we introduce for the first time a useful and convenient mathematical protocol to locate the stationary points along a reaction path. The protocol is quite simple and should convince many organic chemists that certain daunting theoretical treatments can be made easy
0022-3263
7644-7650
Cantillo, David
87273376-7777-4726-bbf9-505104580fad
Ávalos, Martín
472f15e9-0c05-4b63-9566-e3d6e6e70329
Babiano, Reyes
b7ffd91c-bacd-4372-ab99-fc30ac2450ae
Cintas, Pedro
29979233-8382-47a8-bde7-1faf4869308c
Jiménez, José L.
2805f32b-fcee-49fa-8746-53a38ddd40a1
Light, Mark E.
cf57314e-6856-491b-a8d2-2dffc452e161
Palacios, Juan C.
2c06e379-89b3-46b1-95c8-7f5057732f9f
Cantillo, David
87273376-7777-4726-bbf9-505104580fad
Ávalos, Martín
472f15e9-0c05-4b63-9566-e3d6e6e70329
Babiano, Reyes
b7ffd91c-bacd-4372-ab99-fc30ac2450ae
Cintas, Pedro
29979233-8382-47a8-bde7-1faf4869308c
Jiménez, José L.
2805f32b-fcee-49fa-8746-53a38ddd40a1
Light, Mark E.
cf57314e-6856-491b-a8d2-2dffc452e161
Palacios, Juan C.
2c06e379-89b3-46b1-95c8-7f5057732f9f

Cantillo, David, Ávalos, Martín, Babiano, Reyes, Cintas, Pedro, Jiménez, José L., Light, Mark E. and Palacios, Juan C. (2009) Dissecting competitive mechanisms: thionation vs. cycloaddition in the reaction of thioisomu?nchnones with isothiocyanates under microwave irradiation. Journal of Organic Chemistry, 74 (20), 7644-7650. (doi:10.1021/jo900960a).

Record type: Article

Abstract

This paper documents in detail the reaction of 1,3-thiazolium-4-olates (thioisomnchnones) with aryl isothiocyanates. Having demonstrated with a chiral model that thionation occurs under these conditions to provide 1,3-thiazolium-4-thiolates and that this process is actually a stepwise domino reaction (J. Org. Chem. 2009, 74, 3698?3705), we extend this study to monocyclic thioisomnchnones. Herein, competition between thionation and 1,3-dipolar cycloaddition takes place. The process is synthetically disappointing at room temperature requiring prolonged reaction times for completion. The protocol has been subsequently investigated by using both microwave dielectric heating and conventional thermal heating (oil bath) in DMF at 100 °C with an accurate internal reaction temperature measurement. Although a slight acceleration was observed for reactions conducted under microwave irradiation, for most cases the observed yields and chemoselectivities were quite similar. Thus one can conclude that, within experimental errors, the reactivity is not related to nonthermal effects in agreement with recent reassessments on this subject, particularly by Kappe and associates (J. Org. Chem. 2008, 73, 36; J. Org. Chem. 2009, 74, 6157). The whole reaction system, which includes numerous heavy atoms, can be computationally modeled with a hybrid ONIOM[B3LYP/6-31G(d):PM3] level. This reproduces well experimental results and suggests a sequential mechanism. To further corroborate the nonconcertedness, the potential energy surface (PES) has been constructed for simplified models, locating the corresponding stationary points. In doing so, we introduce for the first time a useful and convenient mathematical protocol to locate the stationary points along a reaction path. The protocol is quite simple and should convince many organic chemists that certain daunting theoretical treatments can be made easy

Full text not available from this repository.

More information

Published date: October 2009

Identifiers

Local EPrints ID: 179433
URI: https://eprints.soton.ac.uk/id/eprint/179433
ISSN: 0022-3263
PURE UUID: 8814bb1a-c3a6-45f7-8ee4-0858e99975aa
ORCID for Mark E. Light: ORCID iD orcid.org/0000-0002-0585-0843

Catalogue record

Date deposited: 08 Apr 2011 09:02
Last modified: 06 Jun 2018 12:54

Export record

Altmetrics

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of https://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×