BF3-Induced Rearrangement of Aziridino Cyclopropanes Derived from 2-Phenylsulfonyl 1,3-Dienes. Application to the Total Synthesis of (±)-Ferruginine

Total synthesis of the alkaloid (+/-)-ferruginine (1) has been developed via the 2-phenylsulfonyl 1,3-diene approach. BF(3)-induced rearrangement of the N-protected cyclohexane aziridino cyclopropane 8, derived from its corresponding epoxy cyclopropane, afforded the desired tropane alkaloid skeleton 9 in good yield. Michael addition of nitroethane (as an acyl anion equivalent) and transformation of the nitro group of the adduct 10 to a keto function gave 11. Elimination of benzenesulfinic acid and subsequent replacement of the tosyl group by a methyl group afforded the title compound 1.