Hydrochloric Acid → (R,R)-Diisopropyl tartrate (E)-crotylboronate

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An oven-dried 1Lthree-neck round bottom flask equipped with a magnetic stir bar and a −100° C. thermometer was charged with 206 mL of anhydrous THF and KOtBu (28.2 g, 250 mmol). This mixture was flushed with Ar and cooled to −78° C., then trans-2-butene (23 mL, 250 mmol), condensed from a gas lecture bottle into a rubber-stoppered round bottom flask immersed in a −78° C. dry ice-acetone bath, was poured into the reaction mixture. n-BuLi (100 mL, 2.5 M in hexane) was then added dropwise via cannula over 1.5 h. After completion of the addition, the cooling bath was removed and the reaction mixture was allowed to warm to an internal temperature of −50° C. for 15 min then immediately recooled to −78° C. Triisopropylborate (57.8 mL, 250 mmol) was added drop-wise via cannula to the (E)-crotylpotassium solution over 2 h. After addition, the reaction mixture was maintained at −78° C. for 30 min and then rapidly poured into a 2L separatory funnel containing 470 mL of 1 N HCl saturated with NaCl. The aqueous layer was adjusted to pH 1 by using 1 N HCl (100-150 mL), and then a solution of (R,R)-diisopropyl tartrate (52.8 g, 250 mmol) in 88 mL of Et2O was added. The phases were separated, and the aqueous layer was extracted with additional Et2O (4×120 mL). The combined extracts were dried over MgSO4 for 1 h then vacuum filtered through a fritted glass funnel under Ar blanket into an oven-dried round-bottom flask. The filtrate was concentrated in vacuo, and pumped to constant weight at under vacuum. Anhydrous toluene (170 mL) was added to the flask make a 1M solution.

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