Synthesis of the Enantiomeric Furobenzofurans, Late Precursors for the Synthesis of (+)- and (-)-Aflatoxins B1, B2, G1, and G2

Article abstract of DOI:10.1021/jo00093a008

Enantiomeric tetrahydrofuro<2,3-b>benzofurans, representing the ABC tricyclic portion of aflatoxins B₁, B₂, G₁, and G₂, were generated from the oxaza-Cope rearrangement of a suitably functionalized O-aryloxime.The O-aryloxime was, in turn, made from the condensation of an enantiomerically pure aldehyde derived from glutamic acid and a substituted phenoxyamine.High regioselectivity with respect to the A-ring substituents of the ABC tricycle was achieved through the use of electrochemistry.The regioselective electrochemical cleavage of 4,6-bis(tosyloxy)-2-(methoxycarbonyl)- 2,3,3a,8a-tetrahydrofuro<2,3-b>benzofuran (22) resulted in a 97/3 mixture of regioisomeric phenols.The regiochemical assignments of the resulting phenols were determined by 2D NOESY NMR.The enantiomeric ratio of the final product was determined to be 96/4 by NMR analysis of diastereomers resulting from the coupling of 31a to (+)- and (+/-)-phenethylamine.