Marta Ximenis, Santiago Cañellas, Rosa M. Gomila, Bartomeu Galmés, Antonio Frontera, Antonio Costa and Carmen Rotger
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Reaction contest: hydrolysis versus intramolecular cyclisation reaction in alkyl squaramate esters†
The stability and hydrolytic behavior of squaramate esters in aqueous solutions have been investigated. The structure of squaramates and the nature of adjacent groups significantly influence their aqueous stability and reactivity towards nucleophiles. Squaramate esters, lacking or containing weakly basic neighboring group participation (NGP) substitutions, remain stable up to pH 9. Their hydrolysis rate (kOH ≈ 10−1 M−1 s−1) is 1000 times faster than that of squaramides, following a second-order rate law. Squaramate esters functionalized with basic NGP groups, such as amines, display a pH-dependent hydrolysis rate due to anchimeric assistance of the terminal amino group, reducing stability to pH 5. However, when the squaramate ester has a terminal nucleophilic group in the γ position of the alkyl chain, it undergoes rapid intramolecular cyclization, forming cyclic squaramides.
期刊介绍:
An international, peer-reviewed journal covering all of the chemical sciences, including multidisciplinary and emerging areas. RSC Advances is a gold open access journal allowing researchers free access to research articles, and offering an affordable open access publishing option for authors around the world.