Use of a boroxazolidone complex of 3-iodo-L-tyrosine for palladium-catalyzed cross-coupling.

Complexation of 3-iodo-L-tyrosine with 9-borabicyclo[3.3.1]nonane (9-BBN) provides a convenient substrate for a palladium-catalyzed coupling reaction. The complex is stable to silica gel chromatography (hexanes/ethyl acetate), dilute triethylamine in THF, and potassium fluoride in DMF. The desired product, 3-ethynyl-L-tyrosine, was released from the complex by simply diluting its solution in methanol with chloroform. Interestingly, the complex remains stable in solutions of either methanol or chloroform individually.