Tyrosine O-methyl ether

Synthesis of Enantiomerically Pure p-Amino Acid from 2-tert-Butyl-1-carbomethoxy-2,3-dihydro-4(1 H)-pyrimidinone (S)-p-Tyrosine-O-methyl Ether. 

Danishefsky and Cain examined several amino acids for asymmetric aldolization of trione (118 equation 141).163 With L-proline, the hydrindenedione (119) was obtained in only 27% ee. However, L-pheny-lalanine was more effective, giving (119) with 85% ee. Other amino acids (tyrosine O-methyl ether. 

The iodonium salt shown with N-protected O-methyl tyrosine (sodium salt) in dimethytformamide at 90-95X gave the diaryl ether in 51% yield without racemisation, under these preferred milder conditions rather than by the Ullmann reaction (ref.67). 

The synthesis starts from the A-Boc-tyrosine methyl ester, which was O-benzylated, since the prenyl ether required in the target compound is not compatible with the conditions required for the preparation of the hydoxylamine or the hydrogenation of the isoxazolidine intermediate (Scheme 40). Following cleavage of the A-Boc, the resulting primary amine was treated with anisaldehyde, and after oxidation with m-CPBA... 

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