Endo-benzonorbornen-2-ol as an efficient non-natural chiral auxiliary in the asymmetric aza-Diels-Alder reactions between cyclopentadiene and (1-phenylethyl)iminoacetates (original) (raw)

Exo-2-azabicyclo[2.2.1]hept-5-enes were obtained by cycloaddition reactions between cyclopentadiene and protonated (S)-and (R)-1phenylethylimines of (1R,endo)-benzonorbornen-2-yl glyoxylate. The non-natural (1R,endo)-benzonorbornen-2-ol proved to be an efficient chiral auxiliary in these asymmetric aza-Diels-Alder reactions, which afforded only exo-cycloadducts with 1S : 1R diastereomeric ratios of 15 : 85 for (S)-(1-phenylethyl)imine and 93 : 7 for (R)-(1-phenylethyl) Scheme 1 Synthesis of aza-Diels-Alder adduct 1. † Electronic supplementary information (ESI) available: NMR spectra of 4a, 4b, 5a