The procedure of Baumm et al, Synthetic Communication 1987, 17(14), 1709-1716, was used. To a stirred solution of 0.0561 g (0.156 mmol) of the product of Step 2 and 0.041 g (0.171 mmol) of 4-acetamidobenzenesulfonyl azide in 2 ml of anhydrous acetonitrile 0.065 ml (0.47 mmol) of triethylamine was added at 0° C. After stirring for 3 hours at room temperature the solvent was evaporated to dryness under reduced pressure and the residue was purified by flash column chromatography (silica gel, methylene chloride) to give 0.059 g (98% yield) of 3-methoxyphenyl 2-diazo-3-oxo-3-(3,4,5-trimethoxyphenyl)propanoate. This was dissolved in 2 ml of anhydrous methylene chloride and 3.5 mg (7.9 μmol) of rhodium (III) acetate was added at room temperature under nitrogen atmosphere. The resulting mixture turned deep green after 1 h of stirring at room temperature. After filtration through Celite and washing with fresh methylene chloride, the filtrate was evaporated to dryness under reduced pressure to give the title compound as an deep yellow crystals (0.049 g, 91%); 1H NMR (CDCl3) δ 3.8 (s, 3H, OMe); 3.9 (s, 6H, OMe); 3.94 (s, 3H, OMe); 6.58 (dd, 1H, CH aromatic, J=2.4 Hz; 8.6 Hz); 6.76 (d, 1H CH aromatic; J=2.4 Hz); 7.04 (s, 2H, CH aromatic); 7.25 (d, 1H, CH aromatic, J=8.6 Hz).
