Trimethyl borate → Boronic acid, (4-ethylphenyl)-

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Reaction Steps

A solution of 1-bromo-4-ethyl benzene (2.0 g, 11 mmol) in dry ether (5 ml) was added to magnesium turnings (311 mg, 13 mmol), which had been suspended in dry ether, by dropwise addition. After addition was complete, the suspension was refluxed for a period of 15 min, by which time nearly all of the magnesium had reacted. The solution was then added to trimethyl borate (1.12 g, 11 mmol), previously dissolved in ether (5 ml) at −78° C., warmed to room temperature and stirred for 90 min. The reaction was quenched by the addition of 10% aqueous HCl (2 ml) and the solution was extracted with ether. The combined ether extract was extracted with 1 M NaOH (2×20 ml), the aqueous extracts were acidified with dilute HCl to pH 2 and extracted with ether (2×25 ml). The resulting combined ether extract was washed once with water (10 ml), dried and evaporated to produce a white solid (676 mg, 38% yield), m.p. 138-140° C.

Provenance & Evidence