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Paper | Regular issue | Vol 75, No. 10, 2008, pp.2459-2475
Published online, 26th May, 2008
DOI: 10.3987/COM-08-11410
Reactivity of (R)-4-Phenyloxazolidine-2-thione Chiral Auxiliary: From Deprotection to Heterocyclic Interconversion

Jean-Christophe Monbaliu, Bernard Tinant, and Jacqueline Marchand-Brynaert*

*Unité de Chimie Organique et Médicinale, Département de Chimie, Université catholique de Louvain, Bâtiment Lavoisier, Place Louis Pasteur 1, B-1348 Louvain-la-Neuve, Belgium

Abstract

Using (R)-3-benzyl-4-phenyloxazolidin-2-thione (2) as model compound, a sequence of reactions has been established that allows the chiral auxiliary deprotection to furnish a primary amine. Treatment of 2 with ethyl triflate (3b) followed by ring opening with RbI (4b) and HI elimination with DBU, in a one pot process, gave S-ethyl-N-benzyl-N-1-phenylvinylcarbamothioate (5, 95% yield) which acid hydrolysis (9) and saponification liberated benzylamine. Through a mechanistic study, we showed that the activated chiral oxazolidin-2-thione 3b is a tunable intermediate towards the corresponding oxazolidin-2-one 7, thiazolidin-2-one 8 and thiazolidin-2-thione 10. All those reactions were chemoselective and preserved the chiral center. A structural analysis of this series of heterocycles, by NMR and X-ray diffraction, has been performed.