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1,3,5-Oxadiazine Framework by Oxygen vs. Nitrogen Trapping of an N-Acyliminium Ion Derived from N,O-bis-TMS Pyroglutamic Acid
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International audience. We report that the reaction of N,O-bis-TMS pyroglutamic acid with aldehydes, under basic or acid catalysis leads to O-bis-TMS adducts. Treatment of these N,O-acetals by TfOH affords azalactones or N,N′-substituted methylene-bis-pyroglutamic acids from the trapping of N-acyliminium species, respectively, with oxygen or nitrogen atom intramolecularly versus intermolecularly. Anodic oxidation of the amido acids, followed by diastereoselective oxa-cyclisation of new N-acyliminium salts, provides exclusively fused meso-1,3,5-oxadiazines with the stereochemistry secured by X-ray analysis. The reactivity of these skeletons under both alkaline and acid conditions was also envisioned and discussed. © 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim
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