Hexane → Lithium cyclohexylisopropylamide

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A solution of 0.315 mL of freshly distilled isopropylcyclohexylamine in 2 mL of dry tetrahydrofuran (THF) was placed in a 25 mL flask. A second solution was prepared by dissolving 0.315 mL of the same amine in 1.5 mL of THF in a 5 mL flask. Both solutions were cooled to -78° C. while stirring under an inert atmosphere and treated with 1.2 mL of a 1.6 mL of a 1.6M hexane solution of n-butyllithium, dropwise from a syringe over 1.5 minutes in order to form lithium isopropylcyclohexylamide. To the first solution was added, dropwise over six minutes, 500 mg of (14) in 1 mL of THF. The reaction was stirred at -78+ C. for five minutes, then a solution of 0.12 mL of diethyl carbonate in 0.5 mL of THF was added, dropwise over ten minutes via syringe. After three additional minutes, the second solution of lithium isopropylcyclohexylamide was added followed by an additional 0.12 mL of diethyl carbonate. After 20 minutes at -78° C., the reaction was allowed to warm to room temperature and stir for ten minutes following which it was neutralized with 0.2 mL of acetic acid in 2 mL of H2O. The reaction was partitioned between 100 mL of H2O and 35 mL of ether. The ether phase was separated, dried, filtered, evaporated, and the residue dried under high vacuum to give a yellow oil. It was chromatographed on 60 g of silica gel eluting with 29:1 [v/v] CH2Cl2 :EtOH. Nine mL fractions were collected. Fractions 29-51 were combined and evaporated to give 548 mg (86% yield) of the ester (15) as a clear pale-yellow oil.

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