A Stereoselective Oxidative Dimerization En Route to (-)-Lomaiviticin A

We describe a stereoselective synthesis of the dimeric diazofluorene 15, a potential precursor to the cytotoxic C₂-symmetric bacterial metabolite (-)-lomaiviticin A (1). An efficient route was developed to convert the tetracyclic diol 5 to the diketone 4 (five steps, 30% overall). Oxidative dimerization of the enoxysilane 14 provided the C₂-symmetric dimeric diazofluorene 15 in 56% yield and with 15:1:0 diastereoselectivity. Deprotection and 2D NMR analysis indicated that the major diastereomer possessed the (2S,2'S) configuration found in 1. This approach may ultimately be useful in the synthesis of 1 itself.