Endo-1-Phenylborneol as a novel, alternative chiral auxiliary for the aza-Diels-Alder reaction

Abstract

We report the synthesis and preliminary evaluation of (1S,2S,4R)-7,7-dimethyl-1-phenylbicyclo[2.2.1]heptan-2-ol 1a, which was obtained in 3 steps from inexpensive starting materials, as a chiral auxiliary. The potential for asymmetric induction was investigated by carrying out aza-Diels-Alder reactions with cyclopentadiene and imine derivatives of 1a from (R)-(+)-1-phenylethylamine, (S)-(−)-1-phenylethylamine and benzylamine. The results showed marked exo selectivity and good diastereoisomeric excess when 1a was combined with (R)-(+)-1-phenylethylamine. These results are comparable with those reported using (−)-8-phenylmenthol, suggesting that 1a can represent an economically viable alternative to current chiral auxiliaries.