Synthesis of enantiomerically pure constrained gamma-hydroxy-alpha-amino acids by directed hydroxylation

Efficient synthetic routes to enantiomerically pure (1R,3R,6R)- and (1S,3S,6S)-1-amino-3-hydroxy-6-phenylcyclohexane-1-acids have been developed. The key step is a directed hydroxylation through an iodo-initiated O-functionalization reaction of methyl (1S,6R)- and (1R,6S)-1-aminocarbonyl-6-phenyl-3-cyclohexene-1-carboxylates, which can easily be obtained from the asymmetric Diels-Alder reactions of 1,3-butadiene with the (E)-2-cyanocinnamates of (S)-ethyl lactate and (R)-pantolactone, respectively. (C) 1997 Elsevier Science Ltd.