mek 200 ml were stirred under reflux conditions for 6 hours the cold mixture was filtered off and solids on the filter was washed with mek 100 ml the combined filtrates were evaporated under reduced pressure at 90 u00b0 c to give the mixture of methyl 4 3 bromopropoxy benzoate and dimethyl 4 4 u2032 1 3 propanediylbis oxy bisbenzoate 41 00 g analytical samples of methyl 4 3 bromopropoxy benzoate 17a methyl 4 4 u2032 1 3 propanediylbis oxy bisbenzoate 20 isolated from the mixture by column chromatography on silica gel methyl 4 3 bromopropoxy benzoate 17a 1 h nmr cdcl 3 7 95 d j 8 8 hz 2h 6 88 d j 8 8 hz 2h 4 11 t j 7 0 hz 2h 3 84 s 3h 3 56 t j 7 0 hz 2h 2 29 m 2h dimethyl 4 4 u2032 1 3 propanediylbis oxy bisbenzoate 20 1 h nmr cdcl 3 7 96 d j 8 8 hz 4h 6 90 d j 8 8 hz 4h 4 20 t j 7 0 hz 4h 3 86 s 6h 2 28 m 2h a solution of the mixture of methyl 4 3 bromopropoxy benzoate 17a methyl 4 4 u2032 1 3 propanediylbis oxy bisbenzoate 20 previous step 19 12 g and dibutylamine 27 14 g 35 7 ml 210 mmol in toluene 50 0 ml was stirred under reflux conditions for 3 hours cooled.