3‐Amino‐Substituted Isothiazole <i>S</i>,<i>S</i>‐Dioxides as Dienophiles in Diels–Alder Cycloaddition Reactions with Cyclic, Acyclic and Heterocyclic Dienes

Clerici, Francesca; Casoni, Alessandro; Gelmi, Maria Luisa; Nava, Donatella; Pellegrino, Sara; Sala, Alessandro

doi:10.1002/ejoc.200600369

Cited by 4 publications

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“…It is well known that Diels -Alder reactions can be catalyzed with Lewis acids [9]. For this reason, we selected two catalysts, i.e., ZnI 2 and [Sc(OTf) 3 ], and the cycloaddition reactions were repeated at room temperature and under ultrasound irradiation at 508. In both cases, high yields were obtained in a very short reaction time but without any differences in terms of the diastereoisomer ratio.…”

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“…In both cases, high yields were obtained in a very short reaction time but without any differences in terms of the diastereoisomer ratio. The two diastereoisomers 7 were easily separated by column chromatography, and the endo or exo configuration was determined by considering the chemical shifts in the 1 H-NMR spectra and confirmed by performing NOE experiments and by comparison with analogous adducts [3]. The preferred formation of the endo isomer is not unexpected according to the endo rule of Diels -Alder reactions [10].…”

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Fused Isothiazole S‐Oxide Systems from Cycloaddition Reactions of N‐Benzylisothiazol‐3‐amine 1‐Oxide

Clerici¹,

Casoni²,

Contini³

et al. 2009

Helvetica Chimica Acta

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The racemic N-benzylisothiazol-3-amine 1-oxide (2) was demonstrated to be an efficient partner in Diels -Alder reactions (Schemes 2 -4) and a good dipolarophile in 1,3-dipolar cycloaddition reactions with nitrile oxides (Scheme 5). Polycyclic isothiazole S-oxides with different substitution patterns were obtained from 2 in good yield and in a fully regioselective way. Improved diastereoselection was observed performing the Diels -Alder or 1,3-dipolar cycloaddition reactions in H 2 O.Introduction. -Recently, we described the synthesis of chiral racemic isothiazolamine S-oxides A, starting from the corresponding isothiazolamines 1, and some preliminary studies on their reactivity toward S-nucleophiles which demonstrated the ability of the sulfoxide moiety to direct the addition affording the corresponding 5-(aryl-and alkylthio) derivatives in a fully diastereoselective way (Scheme 1) [1]. The availability of these new S-oxides A prompted us to continue our research on their reactivity. In particular, we concentrated our attention on the aptitude of this system to act as an effective reaction partner in cycloaddition reactions which would allow the preparation of fused isothiazole S-oxide derivatives of both chemical and pharmacological interest. In fact, cycloaddition reactions appeared to be a very versatile tool to obtain new classes of isothiazoles or fused isothiazole systems or new or known heterocycles by the transformation of the primary cycloadducts similarly to the transformations described for the corresponding S,S-dioxides [2 -6]. The exploitation of the sulfoxide system could be considered of large interest due to the significant stereodifferentiating ability of the sulfinyl function [7]. Moreover, taking into account the general interest in environmental contamination, efforts were devoted in this work to develop cycloaddition processes with reduced environmental impact.

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