Medicinal plants of Southern Africa. Part 4. Synthesis of brackenin-like molecules from 1,4-dicarbonyl precursors and by oxidative coupling. X-Ray molecular structure of racemic-2,3-dibenzyl-1,4-diphenylbutane-1,4-dione
Oxidative coupling of appropriate trimethylsilyl enol ethers is shown to give 1,4-diaryl-1,4-diketones in acceptable yields. Subsequent dibenzylation of these intermediates affords compounds related to the naturally occuring brackenin (1). Examination of these products by 1H n.m.r. and 13C n.m.r. demonstrates that these techniques can be used for the determination of relative configurations without resorting to X-ray crystallography.