Er. Civitello et H. Rapoport, SYNTHESIS OF THE ENANTIOMERIC FUROBENZOFURANS, LATE PRECURSORS FOR THE SYNTHESIS OF (-AFLATOXINS AND (-)-AFLATOXINS B-1, B-2, G(1), AND G(2)()), Journal of organic chemistry, 59(14), 1994, pp. 3775-3782
Enantiomeric tetrahydrofuro[2,3-b]benzofurans, representing the ABC tr
icyclic portion of aflatoxins B-1, B-2, G(1), and G(2), were generated
from the oxaza-Cope rearrangement of a suitably functionalized O-aryl
oxime. The O-aryloxime was, in turn, made from the condensation of an
enantiomerically pure aldehyde derived from glutamic acid and a substi
tuted phenoxyamine. High regioselectivity with respect to the A-ring s
ubstituents of the ABC tricycle was achieved through the use of electr
ochemistry. The regioselective electrochemical cleavage of arbonyl)-2,
3,3a,8a-tetrahydrofuro[2,3-b]benzofuran (22) resulted in a 97/3 mixtur
e of regioisomeric phenols. The regiochemical assignments of the resul
ting phenols were determined by 2D NOESY NMR. The enantiomeric ratio o
f the final product was determined to be 96/4 by NMR analysis of diast
ereomers resulting from the coupling of 31a to (+)- and (+/-)-phenethy
lamine.