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Issue 20, 2019
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Mechanistic insights for the transprotection of tertiary amines with Boc2O via charged carbamates: access to both enantiomers of 2-azanorbornane-3-exo-carboxylic acids

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Abstract

Herein we present a new synthesis methodology for the transprotection of the 1-phenylethyl protected tertiary amines to tert-butyloxycarbonyl (Boc) derivatives under exocyclic N–C hydrogenolysis catalyzed by Pd/C. We provide mechanistic insights into the N-dealkylation of hindered tertiary amines under the unrecognized role of tert-butyloxycarbonyl anhydride (Boc2O) as an additive to effectively promote the exocyclic N–C hydrogenolysis of tertiary amines by disclosing the role of Boc2O, which was not fully understood and studied until now. NMR and in silico experiments suggest the formation of a transient charged carbamate as the plausible intermediate. This selective transprotection enabled the development of a robust stereoselective methodology for the preparation of both enantiomers of 2-azanorbornane-3-exo-carboxylates by highly asymmetric aza-Diels–Alder reactions using (−)-8-phenylmenthol (8PM) and (+)-8-phenylneomenthol (8PnM) as chiral auxiliaries.

Graphical abstract: Mechanistic insights for the transprotection of tertiary amines with Boc2O via charged carbamates: access to both enantiomers of 2-azanorbornane-3-exo-carboxylic acids

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Publication details

The article was received on 30 Jul 2019, accepted on 28 Aug 2019 and first published on 29 Aug 2019


Article type: Research Article
DOI: 10.1039/C9QO00957D
Org. Chem. Front., 2019,6, 3540-3554

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    Mechanistic insights for the transprotection of tertiary amines with Boc2O via charged carbamates: access to both enantiomers of 2-azanorbornane-3-exo-carboxylic acids

    I. E. Sampaio-Dias, S. C. Silva-Reis, L. Pinto da Silva, X. García-Mera, M. A. Maestro and J. E. Rodríguez-Borges, Org. Chem. Front., 2019, 6, 3540
    DOI: 10.1039/C9QO00957D

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