Journal
CHEMCATCHEM
Volume 11, Issue 4, Pages 1228-1237Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cctc.201801934
Keywords
palladium-catalysis; DFT calculations; carbocyclization; borylation; cascade reaction
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Funding
- National Natural Science Foundation of China [21772020]
- Fundamental Research Funds for the Central Universities (Chongqing University) [2018CDXZ0002]
- Natural Science Foundation of Shandong Province [ZR2018LB016]
- Education Department of Shandong Province [18KA094]
- Talent Team Culturing Plan for Leading Disciplines of University in Shandong Province
- Basic and Frontier Research Project of Chongqing Science and Technology Commission [cstc2017jcyjAX0371]
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Density functional theory calculations were performed to reveal the mechanisms of Pd-catalyzed cascade carbocyclization-borylation and arylation reactions. The computational results indicate that the reactions start with allylic C-H cleavage through concerted metalation-deprotonation and an intramolecular exo-type allene insertion to form a six-membered carbocycle intermediate. The regioselectivity of insertion could be explained by frontier molecular orbital theory and natural population analysis calculation. In the absence of extra nucleophiles, eta(1)/eta(3)-isomerization followed by acetate-assisted deprotonation could yield polyene product. When nucleophile was added to the reaction system, transmetalation and subsequent reductive elimination could give the exo-substituted triene as major product. Meanwhile, eta(1)/eta(3)-isomerization, transmetalation, and reductive elimination could afford the endo-isomer as side product. The regioselectivity of further functionalization is controlled by the competition of transmetalation and eta(1)/eta(3)-isomerization. The computational results show that both exo- and endo-boronation product could be observed when bis(pinacolato)diboron is added as nucleophile. However, only exo-phenylation product is observed when phenylboronic acid is used as nucleophile because of the high free-energy barrier for reductive elimination from aryl eta(3)-allylic palladium.
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