An unusual oxidative rearrangement of azabicyclo[2.2.1]heptenes, providing a stereoselective route to 2'- and 3'-hydroxycyclopentylglycines

Treatment of the azabicyclo[2.2.1]heptene derivative 4 with mCPBA for 3-5 seconds generates the oxazabicyclo[3.2.1]octene derivative 7 (X-ray structure) via rapid Meisenheimer rearrangement of the N-oxide 5, whilst heating 7 in MeCN for 4-6 h leads to further rearrangement to the more thermodynamically stable oxazabicyclo[3.3.0]octene isomer 6; 6 and 7 can be readily reduced to enantio-pure hydroxylated cyclopentylglycine derivatives.