Santonox → (1R,2S,5S)-6-oxa-3-aza-bicyclo[3.1.0]hexane-2,3-dicarboxylic acid 2-benzyl ester 3-tert-butyl ester

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Reaction Steps

To a solution of (S)-2,5-dihydro-pyrrole-1,2-dicarboxylic acid 2-benzyl ester 1-tert-butyl ester (6.14 g, 20.2 mmol) were added 3-chloroperbenzoic acid (6.99 g, 40.5 mmol) and 4,4′ thiobis(6-tert-butyl-m cresol) (0.726 g, 2.02 mmol). The mixture was refluxed under nitrogen atmosphere overnight then an additional batch of 3-chloroperbenzoic acid (6.99 g, 40.5 mmol) and 4,4′ thiobis(6-tert-butyl-m cresol) (0.726 g, 2.02 mmol) was added. Refluxing was continued for 24 h. The reaction mixture was diluted with CH2Cl2, washed with sodium metabisulphite aqueous (5%), saturated aqueous NaHCO3, brine, dried over Na2SO4, filtered and concentrated. The diastereomeric epoxides in a ratio of 65/35 (determined by NMR on the crude mixture) were separated by flash column chromatography (c-hexane to c-hexane/EtOAc 4:1) to give (1R,2S,5S)-6-oxa-3-aza-bicyclo[3.1.0]hexane-2,3-dicarboxylic acid 2-benzyl ester 3-tert-butyl ester: TLC, Rf (c-hexane/EtOAc 4:1)=0.20; MS (LC/MS): 220 [MH−Boc]+, 342 [M+Na]+; tR (HPLC conditions f): 2.14 min and (1S,2S,5R)-6-oxa-3-aza-bicyclo[3.1.0]hexane-2,3-dicarboxylic acid 2-benzyl ester 3-tert-butyl ester: TLC, Rf (c-hexane/EtOAc 4:1)=0.15; MS (LC/MS): 220 [MH−Boc]+, 342 [M+Na]+; tR (HPLC conditions f): 2.03 min.

Provenance & Evidence