[3+2] Cycloaddition Reaction Between Bis-substituted Allenoate And N-tosylaldimines

2,3-dihydropyrolidine rings are common moieties for many pharmaceuticals and natural compounds.There is a dearth of applicable metal-free methods for the direct construction of this five-membered aza-heterocycles.Herein,a triphenylphosphine-promoted [3 + 2] cycloaddition reaction between ?,?-bis-substituted allenoates and N-Tosylaldimines followed by alkene isomerization was disclosed,which afforded a series of functionalized 2-pyrroline derivatives in moderate chemical yields with random diastereoselectivities.The structural assignment of the 2-pyrroline product was unambiguously corroborated by single-crystal X-ray analysis.We also attempted to realize an enantioselective catalytic version of the cycloaddition between bis-substituted allenoate and N-tosylaldimine by using bifunctional phosphine-containing chiral catalyst.Using L-tert-Leucine-based phosphine,the reaction proceeded smoothly to deliver the cycloadduct in moderate yield and a random diastereoselectivity with promising enantiomeric excess for further optimization.