Phosphoric Acid → (1-Methyl-1H-indol-4-yl)boronic acid

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Reaction Steps

A solution of Intermediate 51 (4.90 g) in anhydrous THF (30 ml) was cooled to −78° C. under argon atmosphere, then added dropwise with 1.62 M solution of n-butyllithium in pentane (28.8 ml) over 30 minutes and stirred for 30 minutes. The mixture was added dropwise with (iPrO)3B (10.77 ml) over 10 minutes, stirred for 1 hour, then warmed to room temperature and further stirred for 2.5 hours. The reaction mixture was poured into 1.2 N aqueous phosphoric acid (250 ml) added with ice, and extracted with diethyl ether (200 ml×3). The organic layer was extracted with 0.4 N aqueous sodium hydroxide (150 ml×3), and the aqueous layer was acidified with 5 N aqueous hydrochloric acid under ice cooling and extracted with diethyl ether (200 ml×3) again. The organic layer was washed with saturated brine and dried, and then the solvent was evaporated under reduced pressure. The residue was washed with hexane to obtain the title compound (Intermediate 52, 3.17 g).

Provenance & Evidence