(Z)-Selective Hydroboration of Terminal Alkynes

  • Author: ChemistryViews
  • Published: 29 November 2021
  • Copyright: Wiley-VCH GmbH
  • Associated Societies: American Chemical Society (ACS), USA
thumbnail image: (<i>Z</i>)-Selective Hydroboration of Terminal Alkynes

Hydroborations are very commonly used reactions in organic synthesis. For example, alkenyl boronic esters can be synthesized via the hydroboration of alkynes and serve as useful intermediates. There are a variety of examples of transition-metal-catalyzed hydroboration of alkynes to give (E)-alkenyl boronates. (Z)-selective hydroboration reactions of alkynes are less common.

Nobuharu Iwasawa, Tokyo Institute of Technology, Japan, and colleagues have developed a (Z)-selective hydroboration of terminal alkynes (pictured). The team used a rhodium catalyst with a thioxanthene-based PSP-type pincer ligand. They reacted 13 different terminal alkenes with pinacolborane (HBpin) in the presence of [Rh(nbd)2]BF4 (nbd = norbornadiene) and the pincer ligand, using toluene as the solvent. The reactions were performed at 30 °C.

The desired (Z)-alkenyl boronates were obtained in moderate to good yields and with high selectivities. The reaction tolerates a range of functional groups, including ketones and halides. The team proposes a mechanism that involves Rh–vinylidene intermediates.



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