TY - JOUR
T1 - Cobalt-Catalyzed 1,1-Diboration of Terminal Alkynes
T2 - Scope, Mechanism, and Synthetic Applications
AU - Krautwald, Simon
AU - Bezdek, Máté J.
AU - Chirik, Paul J.
N1 - Funding Information:
S.K. gratefully acknowledges the Swiss National Science Foundation for a postdoctoral fellowship. M.J.B. thanks the Natural Sciences and Engineering Research Council of Canada for a predoctoral fellowship (PGS-D). We are grateful to W. Neil Palmer and Jennifer V. Obligacion for insightful discussions. We also thank Dr. István Pelczer for assistance with NMR spectroscopy as well as Dr. Charles Campana (Bruker) for assistance with solving the X-ray structure shown in Scheme 5. The staff at Lotus Separations are gratefully acknowledged for measuring the ee of 12. Financial support was provided by NIH (R01 GM121441).
Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/3/15
Y1 - 2017/3/15
N2 - 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.
AB - 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.
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U2 - 10.1021/jacs.7b00445
DO - 10.1021/jacs.7b00445
M3 - Article
C2 - 28199104
AN - SCOPUS:85015252414
SN - 0002-7863
VL - 139
SP - 3868
EP - 3875
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 10
ER -