Synthesis of the bisbenzannelated spiroketal core of the gamma-rubromycins. The use of a novel Nef-type reaction mediated by Pearlman's catalyst

The synthesis of the bisbenzannelated spiroketal core 6 of the gamma-rubrom ycin 1 from the substituted nitrostyrene 20 was achieved by using a novel N ef-type reaction mediated by Pearlman's catalyst. The precursor 28 was synt hesised from readily prepared starting materials using Henry condensation c hemistry. The product 6 was found to exist in two conformations in solution as shown by NMR spectroscopy.