1. A fine suspension of iodine (25.4 g, 100 mmol) in chloroform (700 mL) was added dropwise to a stirred mixture of 3-methoxyphenol (10.8 mL, 100 mmol), silver trifluoroacetate (22.1 g, 100 mmol) and chloroform (100 mL). It was allowed to stand at room temperature for 2 hours under nitrogen protection. Subsequently, the mixture was stirred under the same conditions for 60 h. The mixture was then filtered through a Celite pad and the pad was rinsed with chloroform.
2. The filtrate was washed sequentially with 0.1 N Na2S2O4 aqueous solution, saturated NaHCO3 solution and water, then the aqueous layer was back-extracted with chloroform. The organic layers were combined, dried with Na2SO4 and concentrated to give 26.6 g of brown oil. The residue was purified by rapid chromatography on silica gel, eluting with chloroform to give 2-iodo-5-methoxyphenol (18.4 g, 74%). ms (IS) 249 (M-1)-.
3. In a dry round-bottomed flask, cuprous(I) iodide (0.28 g, 1.5 mmol) was added to a stirred solution of 2-iodo-5-methoxyphenol (18.4 g, 73.6 mmol) and trimethylmethylsilylacetylene (15.6 mL, 110.4 mmol) in anhydrous THF (225 mL). Dichlorobis(triphenylphosphine)palladium(II) (1.55 g, 2.2 mmol) and diisopropylamine (21.7 mL, 154.5 mmol) were added and stirred at room temperature under nitrogen protection overnight. After completion of the reaction, water was added and extracted with EtOAc (3 times). The organic layers were combined, dried and concentrated with MgSO4 to give 29 g of black oily material. The residue was adsorbed on SiO2 and purified by rapid chromatography on silica gel, eluting with 0-15% EtOAc/hexane to give 5-methoxy-2-trimethylsilyl ethynylphenol (11.5 g, 71%).MS (IS) 221 (M+1)+.
4. diisopropylamine (11.0 mL, 78.3 mmol) was added to a rapidly stirred solution of 5-methoxy-2-trimethylsilylethynylphenol (11.5 g, 52.2 mmol) in CH2Cl2 under nitrogen protection. 2-(Trimethylsilyl)ethoxymethyl chloride (13.9 mL, 78.3 mmol) was added dropwise over 5 min and stirred overnight at room temperature. The reaction mixture was acidified with 1 N HCl aqueous solution and layered with water. The aqueous layer was extracted with CH2Cl2 (2 times), the organic layers were combined, dried with MgSO4 and concentrated. The residue was adsorbed on SiO2 and purified by rapid chromatography on silica gel, eluting with 0-5% EtOAc/hexane to give 4-methoxy-2-(2-trimethylsilyl-ethoxymethoxy)-1-trimethylsilylethynylbenzene (13.5 g, 74%). ms (IS) 351 (M+1).
5. A solution of potassium hydroxide (2.3 g, 40.4 mmol) in water (20 mL) was added dropwise to a rapidly stirred solution of 4-methoxy-2-(2-trimethylsilyl-ethoxymethyl)-1-trimethylsilylethynylbenzene (13.5 g, 38.5 mmol) in methanol (200 mL) and stirred for 1 h at room temperature. The reaction mixture was concentrated and brine was added to the residue and extracted with EtOAc (2 times). The organic layers were combined, dried and concentrated with MgSO4 to give 11.7 g of brown oil. The residue was adsorbed on SiO2 and purified by rapid chromatography on silica gel, eluting with 0-10% EtOAc/hexane to give [2-(2-ethynyl-5-methoxy-phenoxymethoxy)-ethyl]-trimethyl-silane (10.0 g, 93%). ms (IS) 279 (M+1)+.
6. 1,4-Phenylene diisocyanate (6.41 g, 40.0 mmol) was added to a stirred solution of [2-(2-vinyl-5-methoxy-phenoxymethoxy)-ethyl]-trimethyl-silane (5.57 g, 20.0 mmol) and ethyl 6-nitro-hexanoate (7.56 g, 40.0 mmol) in anhydrous toluene (150 mL), protected by nitrogen gas stirred under nitrogen. Triethylamine (5.6 mL, 40.0 mmol) was added and refluxed under nitrogen protection over heat. 2 hours later, additional anhydrous toluene (150 mL) was added and refluxing was continued overnight. The mixture was filtered through a Celite pad and rinsed with toluene. The filtrate was concentrated to give 8.7 g of yellow oil. The residue was purified by rapid chromatography on silica gel, eluting first with 0-20% EtOAc/hexanes and then with 0-30% EtOAc/hexanes, to give 2-iodo-5-methoxyphenol (5.20 g, 58%).NOESY confirmed the correct regioselective isomerization.MS (IS) 450 (M+1)+.
