Mechanochemical Diastereoselective Substrate-Directed Synthesis of Pyrrole-Isoxazolidines via 1,3-Dipolar
Iva S de Jesus1, Anna Flávia da C Lédo2, Armando Ferrer1
1Instituto de Química, Universidade Federal da Bahia, Campus de Ondina, Salvador, Bahia40170-115, Brazil.
Abstract:
An efficient and sustainable substrate-directed mechanochemical synthesis of pyrrole-isoxazolidines was developed via the 1,3-dipolar cycloaddition of maleimides with nitrones. Moderate to good yields were generally obtained, and the diastereoselectivity is influenced by the steric (to N-alkyl nitrones) and electronic (EDG or electron-withdrawing group on aryl groups) nature of the substituents and, in some cases, is the opposite of that obtained by solvent-dependent methods. A reinterpretation of the known exo/endo transition states could explain the cis/trans selectivity, and on the basis of this, empirical guidelines are presented for predicting the diastereoselectivity as a function of substituents in this cycloaddition. Furthermore, this mechanochemical approach provided a protocol with short reaction times and simple processing, eliminating the need for column chromatography purification. Scaling up to one product and detailed green metrics to all products indicated that this mechanochemical approach is a greener route in relation to the traditional solvent methods.
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