Cycloaddition of heteroatom-substituted 2-azaallyl anions with alkenes. Synthesis of 1-pyrrolines and bridged azabicyclic compounds

Nonstabilized 2-azaallyl anions bearing heteroatom substituents [(RCHNC)-C- 1(X)R-2(-)Li(+), where R-1 and R-2 are hydrogen or alkyl groups and X = OMe , SPh, or NR2] were generated and found to undergo efficient [3 + 2] cycloa dditions with alkenes to provide 1-pyrrolines after loss of LiX. The 2-azaa llyl anions were generated by tin-lithium exchange on stannyl imidates, thi oimidates, or amidines (RCH)-C-1(SnBu3)N=C(X)R-2 with n-butyllithium. The i nitially formed 1-pyrrolines were found to be deprotonated under the reacti on conditions to afford 1-metalloenamines, which could be quenched with alk yl halides, carbonyl compounds, or MeSSMe to provide further functionalized 1-pyrrolines. Cyclic methoxy-substituted 2-azaallyl anions were generated and were found to undergo cycloadditions with alkenes to afford bridged aza bicyclic compounds (1-methoxy-7-azabicyclo[2.2.1]heptanes and 1-methoxy-8-a zabicyclo[3.2.1]octanes). These are the first examples of cyclic nonstabili zed 2-azaallyl anions.