Expedient Enantioselective Synthesis of the Δ4-Oxocene Cores of (+)-Laurencin and (+)-Prelaureatin

An expedient enantioselective synthesis of the Delta(4)-oxocene cores present in (+)-laurencin and (+)-prelaureatin was accomplished in eight steps via a novel one-pot regio- and stereoselective ring cyclization fragmentation expansion cascade from the tetrahydrofuran precursors which were prepared by stereocontrolled cyclization from vinylsilanes. This process is highlighted by an intramolecular oxo-carbenoid insertion and a beta-silyl fragmentation sequence.