Synthesis
The general procedure for the synthesis of 5-bromobenzofuran from 4-bromophenoxyacetaldehyde diethyl acetal was as follows: polyphosphoric acid (10 g) was added to a solution of benzene (50 mL), the product of step A (8.4 g). The reaction mixture was heated to reflux for 4 hours. Upon completion of the reaction, the mixture was cooled to 0 °C and slowly poured into ice water (80 mL). The aqueous phase was extracted with ether and the organic phases were combined. The ether layer was washed sequentially with saturated sodium bicarbonate solution and brine, dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to give 4.9 g of crude product in 85% yield.
References
[1] Patent: WO2004/33440, 2004, A1. Location in patent: Page 239-240
[2] Patent: US2004/147559, 2004, A1. Location in patent: Page 122
[3] Patent: US2004/106794, 2004, A1. Location in patent: Page 123
[4] Patent: WO2005/66147, 2005, A1. Location in patent: Page/Page column 209
[5] Patent: WO2005/68460, 2005, A1. Location in patent: Page/Page column 203
