Cobalt-Catalyzed 1,1-Diboration of Terminal Alkynes: Scope, Mechanism, and Synthetic Applications

Simon Krautwald, Máté J. Bezdek, Paul J. Chirik

Research output: Contribution to journalArticle

64 Scopus citations

Abstract

A cobalt-catalyzed method for the 1,1-diboration of terminal alkynes with bis(pinacolato)diboron (B2Pin2) is described. The reaction proceeds efficiently at 23 °C with excellent 1,1-selectivity and broad functional group tolerance. With the unsymmetrical diboron reagent PinB-BDan (Dan = naphthalene-1,8-diaminato), stereoselective 1,1-diboration provided products with two boron substituents that exhibit differential reactivity. One example prepared by diboration of 1-octyne was crystallized, and its stereochemistry established by X-ray crystallography. The utility and versatility of the 1,1-diborylalkene products was demonstrated in a number of synthetic applications, including a concise synthesis of the epilepsy medication tiagabine. In addition, a synthesis of 1,1,1-triborylalkanes was accomplished through cobalt-catalyzed hydroboration of 1,1-diborylalkenes with HBPin. Deuterium-labeling and stoichiometric experiments support a mechanism involving selective insertion of an alkynylboronate to a Co-B bond of a cobalt boryl complex to form a vinylcobalt intermediate. The latter was isolated and characterized by NMR spectroscopy and X-ray crystallography. A competition experiment established that the reaction involves formation of free alkynylboronate and the two boryl substituents are not necessarily derived from the same diboron source.

Original languageEnglish (US)
Pages (from-to)3868-3875
Number of pages8
JournalJournal of the American Chemical Society
Volume139
Issue number10
DOIs
StatePublished - Mar 15 2017

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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