Synthesis of seco-psymberin/irciniastatin A:: the discovery of a novel PhI(OAc)2 mediated cascade cyclization reaction

The psymberin unsaturated 'psymberate' side chain 7 was synthesized in 7 steps (36% yield) with good diastereoselectivity using commercially available starting material to control the stereochemistry at C-4 and C-5. The synthesis of seco-psymberin was completed in an efficient manner based on a CuI mediated coupling reaction between vinyl iodide 8 and 'psymberamide' 7. In an attempt to synthesize natural psymberin from the seco-intermediate, a novel PhI(OAc)(2) mediated cascade ring closing reaction was discovered. A possible mechanistic pathway for the formation of the ring closing product was presented. (C) 2008 Elsevier Ltd. All rights reserved.