Chemoenzymatic synthesis of unnatural amino acids via modified Claisen rearrangement of glycine enolates: approach to morphine synthesis

Model studies of aminoesters were conducted to determine the effects of Claisen rearrangement on allylic systems in arene cis-diols. Analysis of Claisen rearrangement in four amino esters led to chelate formation of an amino acid product with a reversed alpha-amino configuration. Furthermore, a chair- or boatlike transition state was formed by Claisen rearrangement due to two opposing steric interactions which causes the cylcohexenyl ring to destabilize the chairlike transition state.