Synthesis of oxa-bridged analogues of farnesyltransferase inhibitor RPR 115135

Two synthetic routes to new oxygen-bridged analogues of farnesyltransferase inhibitors are described that follow either a [3 + 2]/[4 + 2] or a [4 + 2]/[3 + 2] sequence of reactions. The first approach has been achieved by reacting the in situ generated phenylisobenzofuran (PIBF) 4 with pyrroline 5a and has led stereoselectively to racemic 18, which was transformed in a few steps into the target molecule 2. The second pathway relies on a key intermediate 6, obtained either by condensation of PIBF with methyl acrylate, followed by a deprotonation/selenation and an oxidation/elimination sequence, or by cycloaddition between PIBF and alpha-phenylselenoacrylate 11, followed by the same oxidation/elimination sequence. The reaction of 6 with amino dipole 7 gives diastereoselective access to pyrrolidine 25, a precursor of the second target 3, an epimer of 2.