Synthesis of biologically active natural products by [3 + 2] cycloaddition of non-stabilized azomethine ylides (AMY): Concepts and realizations

Abstract

Non-stabilized azomethine ylides (AMY) which are represented as a zwitterionic form of a CNC unit having four electrons in three parallel atomic π orbitals perpendicular to the plane of the dipole, undergoes 1,3-dipolar cycloaddition to produce isolated as well as fused pyrrolidine ring system stereoselectively. Various new structural entities related to x-azatricyclo[m.n.0.0a,b]alkanes are constructed by the intramolecular 1,3-dipolar cycloaddition of nonstabilized cyclic azomethine ylides. The ylide is generated by the sequential double desilylation of N-alkyl α,α′-bis(trimethylsilyl)cyclic amines using Ag(I)F as a one-electron oxidant. Various alkaloids such as (±)-pancracine, (±)-brunsvigine, (±)-maritidine, (±)-crinine, (−)-vincodifformine and (+)-aspidospermidine have been synthesized employing AMY cycloaddition strategy.