Stereoselective functionalisation of SuperQuat enamides: asymmetric synthesis of homochiral 1,2-diols and alpha-benzyloxy carbonyl compounds

Journal article

Homochiral (E)- and (Z)-enamides derived from SuperQuat (S)-4-phenyl-5,5-dimethyl-oxazolidin-2-one undergo highly diastereoselective epoxidation upon treatment with dimethyldioxirane. Subsequent epoxide opening with meta-chlorobenzoic acid proceeds via a stereoselective SN1-type process, with retention of configuration, to give the corresponding 1′-m-chlorobenzoyl-2′-hydroxy derivatives. Treatment of the SuperQuat enamides with mCPBA effects this two-step transformation in one pot. Reductive cleavage of the isolated 1′-m-chlorobenzoyl-2′-hydroxy derivatives (≥96% de) generates homochiral 1,2-diols in ≥96% ee. Alternatively, regioselective lithiation of the enamide at C(1′) with tBuLi followed by reaction with an aromatic aldehyde and in situ O-benzylation generates a 1′-(benzyloxy-aryl-methyl) substituted enamide with high diastereoselectivity. Subsequent oxidative cleavage of the enamide C{double bond, long}C bond with NaIO4/RuCl3 followed by methanolysis of the resultant N-acyl fragment furnishes an O-benzyl protected α-hydroxy methyl ester in high ee. © 2008 Elsevier Ltd. All rights reserved.

Authors: Aciro, C; Davies, S; Garner, A; Ishii, Y; Key, M

• Publication status: Published
• Journal: TETRAHEDRON
• Volume: 64
• Issue: 39
• Pages: 9320-9344
• Publication date: 2008-09-22
• DOI: 10.1016/j.tet.2008.07.012
• ISSN: 0040-4020
• Language: English
• Keywords: SuperQuat; asymmetric synthesis; 1,2-diols; enamides; oxidation