Synthetic Studies towards Pectenotoxin-2: Synthesis of the Nonanomeric 10-epi-ABCDE Ring Segment by Kinetic Spiroketalization

The synthesis of the nonanomeric 10-epi-ABCDE ring system of pectenotoxin-2 has been achieved by using a kinetic spiroketalization reaction. The synthesis of the spiroketalization precursor was achieved through a cross-metathesis/hydro-genation sequence. The formation of the epi-C10 isomer resulted from an unexpected anti-Felkin selective addition of organometallic nucleophiles to the advanced CDE ring precursor. This addition reaction was investigated with differently protected α,β-dioxygenated model aldehydes, which displayed similar anti-Felkin selectivities with organometallic nucleophiles.