SYNTHESIS OF THE ENANTIOMERIC FUROBENZOFURANS, LATE PRECURSORS FOR THE SYNTHESIS OF (+)-AFLATOXINS AND (-)-AFLATOXINS B-1, B-2, G(1), AND G(2)

Enantiomeric tetrahydrofuro[2,3-b]benzofurans, representing the ABC tricyclic portion of aflatoxins B-1, B-2, G(1), and G(2), 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.