Efficient enantioselective synthesis of condensed and aromatic-ring-substituted tyrosine derivatives

An efficient access to both condensed and conjugated tyrosine analogues of high enantiomeric purity is described. Novel ring-substituted tyrosines were synthesized by Suzuki cross couplings of appropriately protected l-3-iodotyrosine with a series of activated and deactivated boronic acid derivatives to achieve the target compounds in high yields. d- and l-4-hydroxy-1-naphthylalanines were readily prepared from the corresponding alpha-enamide in two different approaches, by asymmetric hydrogenation as well as by unselective hydrogenation and enzymatic resolution of the racemic mixture.