[I:1][C:2]1[CH:3]=[C:4]([CH:11]=[CH:12][C:13]=1[OH:14])[CH2:5][C@@H:6]([C:8]([OH:10])=[O:9])[NH2:7].OS(O)(=O)=O.[CH3:20][C:21](=[CH2:23])[CH3:22].C([O-])(O)=O.[Na+]>O1CCOCC1.O>[I:1][C:2]1[CH:3]=[C:4]([CH:11]=[CH:12][C:13]=1[OH:14])[CH2:5][C@@H:6]([C:8]([O:10][C:21]([CH3:23])([CH3:22])[CH3:20])=[O:9])[NH2:7]
A mixture of 5.0 g of 3-iodo-L-tyrosine (Aldrich) and 2.5 mL of conc. H2SO4 in 85 mL of 1,4-dioxane was added to 30 mL of liquid isobutylene (condensed at -78° C.) in a 300 mL pressure bottle. The vessel was stoppered and the contents stirred at RT. After 3 days the bottle was cooled in an ice water bath, opened and the solution poured into a mixture of 10 g of NaHCO3 in 150 mL of water. The resulting mixture was subjected to rotary evaporation to remove isobutylene and dioxane. A white solid resulted which was collected by filtration and dried in vacuo. Analysis by tlc (SiO2, CH2Cl2 :MeOH) indicated major and minor components at Rf= 0.52 and 0.60 respectively. The crude product was purified by flash chromatography on silica gel (95:5 CH2Cl2 :MeOH) to afford 3.4 g (58%) of tert-butyl 3-iodo-L-tyrosinate as a white crystalline solid, m.p. 158-159° C.
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