Studies on mesoionic compounds. XIII. Synthesis of mesoionic 1,2,3-thiadiazolium-4-thiolates.

Adachi, Jun; Takahata, Hidenobu; Nomura, Keiichi; Masuda, Kazuaki

doi:10.1248/cpb.31.1746

Cited by 10 publications

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“…However, the required stability of NLO materials limits the use of mesoionic systems, unless it can be enhanced by a suitable exchange of the electron-withdrawing exocyclic atoms, namely incorporation of a heavier sulfur atom. Several synthetic procedures, including tandem cycloaddition−retrocycloaddition processes, alkylation with a trialkyloxonium salt followed by the replacement of the resulting alkoxy group by sulfide or hydrogen sulfide anion, or the treatment with Lawesson’s reagent, have been so far described for the conversion of mesoionic olates into mesoionic thiolates. In this context we have recently reported the conversion of imidazo[2,1- b ]thiazolium-3-olate systems ( 1 and 3 ) into the corresponding imidazo[2,1- b ]thiazolium-3-thiolate derivatives ( 2 and 4 ) by reaction with aryl isothiocyanates, and proving unequivocally that this thionation does actually proceed via a domino mechanism …”

Section: Introductionmentioning

confidence: 99%

Dissecting Competitive Mechanisms: Thionation vs. Cycloaddition in the Reaction of Thioisomünchnones with Isothiocyanates under Microwave Irradiation

et al. 2009

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This paper documents in detail the reaction of 1,3-thiazolium-4-olates (thioisomunchnones) 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 thioisomunchnones. 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 degrees 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.

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Section: Introductionmentioning

confidence: 99%