pubs.acs.org/joc
platform for designing different types of chiral ligands.1
An Efficient Catalyst System for Pd-Catalyzed
Amination of [2.2]Paracyclophanyl Bromides
Examples of [2.2]paracyclophane-based ligands include di-
phosphanes,2 oxazoline-phosphanes,3 imidazoliums,4 oxa-
zoline-alcohols,5 and imine ligands.6 Recently, a series of
planar chiral [2.2]paracyclophanyl dihydroimidazoliums
have been prepared by our group7 and their applications as
rhodium7a or ruthenium complexes7b in highly enantioselec-
tive transformations have also been demonstrated.
[2.2]Paracyclophanyl amines are important intermediates
for the synthesis of [2.2]paracyclophanyl carbene precursors
and imine ligands.8,9c Their synthesis has been a topic of
interest in organic chemistry, and although several methods
are available,9 the discovery of new and improved metho-
dology is still of interest. Herein, we present a study on
palladium-mediated substituted [2.2]paracyclophanyl ami-
nation dealing with ligand effects and functional group
tolerance.
Bo Qu, Yudao Ma,* Qingshuang Ma, Xiao Liu, Fuyan He,
and Chun Song*
Department of Chemistry, Shandong University, Shanda
South Road No. 27, Jinan 250100, People’s Republic of China
ydma@sdu.edu.cn; chunsong@sdu.edu.cn
Received June 18, 2009
The Buchwald-Hartwig palladium-catalyzed amination
of aryl halides/triflates has emerged in the last decades as a
powerful tool for the synthesis of arylamines.10 Hartwig and
Buchwald previously reported that benzhydrylideneamine
can function as an effective ammonia equivalent,11 and
Connick adopted this strategy for Pd(BINAP)-catalytic
amination of 4,16-dibromo[2.2]paracyclophane.9c To our
knowledge, this is the only reported example of palladium-
catalyzed amination of [2.2]paracyclophanyl halides with
benzhydrylideneamine as an ammonia equivalent. Although
Pd(BINAP) catalyst is capable of coupling benzhydrylide-
neamine with 4,16-dibromo[2.2]paracyclophane, reaction
with this catalyst has several limitations: the catalyst has a
short lifetime and a limited scope, needs a long reaction time,
and requires large amounts of catalyst.
A practical Buchwald-Hartwig amination of [2.2]paracyclo-
phanyl bromides with benzhydrylideneamine is developed.
The method provides a facile route to a variety of imino and
amino [2.2]paracyclophanes that are otherwise not readily
synthesized.
Planar chiral [2.2]paracyclophane-based ligands possess a
rigid [2.2]paracyclophanyl unit, which provides a versatile
*To whom correspondence should be addressed. Phone: 0086-531-
88361869. Fax: 0086-531-88565211.
We now report on catalysts that overcome these limita-
tions. Our approach, which is based upon the selection
of ligands that combine steric hindrance, strong electron
donation, and tight chelation, leads to a catalyst system
that simultaneously possesses long lifetimes and displays
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DOI: 10.1021/jo901310a Published on Web 08/07/2009
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J. Org. Chem. 2009, 74, 6867–6869 6867
2009 American Chemical Society