Asymmetric synthesis of bicyclic amino acid derivatives by Aza‐Diels‐Alder reactions in aqueous solution

Abstract

Abstract Derivatives 7–10 and 13–16 of methyl and ethyl 2‐azabicyclo[2.2.1]heptane‐3‐carboxylates are synthesized by Aza‐Diels‐Alder reactions of chiral iminium ions, formed in situ from glyoxylic acid and chiral amines, with cyclopentadiene. Whereas the heterodienophiles derived from phenylglycinol and esters of sterically more demanding amino acids fail to undergo asymmetric cycloadditions, with alanine methyl ester and ( R )‐1‐phenylethylamine hydrochoride the cycloadducts are formed in yields of 15 and 52%, respectively, reaching de values of up to 90:10 for the exo isomers.