Skip to main content

Hydroboration of Alkenes/Alkynes

Mechanism + Description

Suprafacial addition of a boron hydride to the electron-rich p-system of an alkene or alkyne.

General comments

Boranes readily add to alkenes and alkynes. With unsymmetrical alkenes, hydroboration occurs in anti-Markovnikov fashion so that boron becomes attached to the less-substituted end of the double bond. BH3 can react with 3 moles of an alkene to form BR3. Less reactive hydroboranes may require transition-metal-catalysis to proceed at a synthetically useful rate. Alkyl boranes are not usually isolated but prepared and reacted further in situ. A classical transformation would be oxidation with H2O2 to give an alcohol. Hydroborations need to be carried out with the regard for the toxicity and flammability of borane (B2H6 = 2 x BH3), and alkylboranes. Borane is spontaneously flammable and can form an explosive atmosphere in air.

Key references

Brown, H. C.; Zweifel, G. A. Stereospecific Cis Hyadration Of The Double Bond In Cyclic Derivatives. J. Am. Chem. Soc. 1959, 81, 247.

Pereira, S.; Srebnik, M. A Study of Hydroboration of Alkenes and Alkynes with Pinacolborane Catalyzed by Transition Metals. Tet. Letts. 1996, 37, 3283-3286.

Brown, H. C.; Chandrasekharan, J. Hydroboration. 65. Relative reactivities of representative alkenes and alkynes toward hydroboration by catecholborane. J. Org. Chem. 1983, 48, 5080-5082.

Yang, K.; Song, Q. Transition-Metal Promoted Hydroborations of Alkenes, Emerging Methodology for Organic Transformations. Chem. Rev. 1991, 91, 1179-1191.

Atkins, W. J.; Burkhardt, E. R.; Matos, K. Safe Handling of Boranes at Scale. Org. Process Res. Dev. 2006, 10, 1292-1295.

Potyen, M.; Josyula, K. V. B.; Schuck, M.; Lu, S.; Gao, P.; Hewitt, C. Borane−THF:  New Solutions with Improved Thermal Properties and Stability. Org. Process Res. Dev. 2007, 11(2), 210-214.

Souto, J. A.; Stockman, R. A.; Ley, S. V. Development of a Flow Method for the Hydroboration/Oxidation of Olefins. Org. Biomol. Chem. 2015, 13, 3871-3877.