Univerzita PardubiceFakulta chemicko- technologická

Univerzita Pardubice

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Inverse neighboring group participation: Explanation of an unusual S?N alkyl migration of isothiuronium salts containing lactone group

Autoři: Hanusek Jiří | Váňa Jiří | Sedlák Miloš | Kammel Richard | Roithová Jana | Škríba Anton | Jašík Juraj

Rok: 2013

Druh publikace: ostatní - přednáška nebo poster

Strana od-do: nestránkováno

Tituly:

Jazyk	Název	Abstrakt	Klíčová slova
eng	Inverse neighboring group participation: Explanation of an unusual S?N alkyl migration of isothiuronium salts containing lactone group	At our department we are constantly dealing with transformation reactions of isothiuronium salts containing either a lactam , , or a lactone , moiety which represent versatile starting materials for synthesis of many important heterocycles including thiazoles, thiazolidines, thiazines, isoindoles etc. Many of these syntheses involve acid-base catalyzed ring transformations (rearrangements) proceeding under very mild conditions, even at physiological pH. Recently, we have studied an unexpected course of rearrangement of substituted S-(1(3H)-isobenzofuranone-3-yl)isothiuronium bromides giving either 2H-isoindol-2-carbothioamides or N,N?-dimethyl-N-(3-oxo-1,3-dihydro-2-benzofuran-1-yl)-thioureas depending on substitution at the isothiuronium moiety. A detailed experimental and DFT study of the S to N alkyl migration of substituted S-(1(3H)-isobenzofuranone-3-yl)isothiuronium bromide to N,N?-dimethyl-N-(3-oxo-1,3-dihydro-2-benzofuran-1-yl)thiourea (see Scheme) provided evidence for the existence of an unusual double displacement mechanism involving two consecutive back-side SN2 reactions where a carboxylate anion has a crucial role both as a leaving group as well as an internal nucleophile. The thiazetidine zwitterionic species which is involved in this mechanism as an intermediate was characterized by infrared multiphoton dissociation spectroscopy and was trapped with methyl iodide. It was found that the intermediate has a structure of a free ion pair. The double displacement mechanism can be considered as a new type of inverse lactone neighboring group participation.	Inverse neighboring group participation; S?N migration; isothiuronium salts; lactone