Ring closure reactions of bicyclic prolinol and prolin ester enantiomers

Abstract

Starting from the of bicyclic proline ester, ethyl exo-2-azabicyclo[2.2.1] heptane-3-carboxylate (+)-5 several hydantoines and thiohydantoines were prepared by acidic ring closure of the corresponding urea or thiourea derivatives. Enantiomer (-)-5 was reduced to 2-azanorbornylmethanol 12, which was transformed to 5,8-methanooxazolo- and thiazolo[3,4-a]pyridine derivatives. The structures, stereochemistry and relative configurations of the synthesized compounds were proved by NMR.