✍ Scribed by Donald S. Matteson; Gerald D. Hurst
No coin nor oath required. For personal study only.
-78°C followed by reawangemenf o f the resulting borate complex 2 s in the presence of zinc chloride at 25°C has resulted in chirally biased insertion of the I -chloroethyl group into the carbon-boron bond. (s)-Pinanediol phenylboronate (7) produced (s)-pinanediol ( I S)-(I -chloro-I-phenylethy1)boronate (8s) in 92% DE. Nonstererospecific reaction with ethylmagnesium bromide to form (s)-pinanediol (I S)-(I -phenyI-1 -methylpro-py1)boronate (5s) reduced the DE to 88%. Peroxidic deboronation yielded (R)-( +)-2-phenyl-2-butanol (6R) (84% EE). (s)-Pinanediol ethylboronate (4) with ( )lithium showed the opposite chiral preference, yielding (s)-pinanediol ( I R)-(I -chloro-I-methylpropy1)boronate (3R) (89% DE), which was converted by phenylmagnesium bromide followed by hydrogen peroxide to 6R (76% EE). Diastereoselections were small in reactions of ( I ,I -dichloroethyl)lithium with n-alkylboronates 9a and 13 and with cyclohexylboronate 9c. The 13 was converted to the enantiomer of the insect pheromone frontalin (17) (21 % EE). Good diastereoselections were found with a-substituted alkylboronates 9b and 18, but the configurations of the products could not be determined. (s)-Pinanediol ( I ,I -dichloroethyl)boronate (1) reacts with Grignard reagents via an intermediate borate 2R with negligible diastereoselection.
📜 SIMILAR VOLUMES
## Abstract Tertiary boronic esters smoothly undergo protodeboronation in the presence of CsF or TBAF in aqueous solution.