To an ice cold (0° C.) solution of [16.8 g, 0.078 mol] 2-(4-methoxyphenyl)-6,7-dihydro-[5H]-pyrrolo[1,2-a]imidazole in 200 ml of dry tetrahydrofuran under argon was added dropwise over 20 minutes 35 mL [0.0858 mol] of a 2.5M solution of n-butyl lithium in hexane. Once the addition was complete, the deep-red solution was stirred in the cold for five minutes and then a solution of the tributyltin chloride [26.4 g, 0.0975 mol] in 50 ml of dry tetrahydrofuran was added over 20 min. The reaction mixture was stirred at ice-bath temperatures for 1.5 hours and then saturated ammonium chloride was added. The layers were shaken together and separated and the organic extract was washed an additional time with saturated ammonium chloride and then dried with anhydrous potassium carbonate. The solvent was removed in vacuo to give 50 g of a crude oil, which was taken up twice in cold hexane, filtering off the unreacted 2-(4-methoxyphenyl)-6,7-dihydro-[5H]-pyrrolo[1,2-a]imidazole each time. The product was purified on a column of silica, eluting with 1:1 ethyl acetate/hexane in the presence of 1% diethylamine, to give 19.2 g (49% of a yellow oil.
