COMMUNICATION
Over the last four decades, catalytic asymmetric transfor-
mations mediated by bio-, transition-metal, and organic cat-
alysts have served as a powerful means to access a wide
range of optically pure compounds.[1] In particular, tremen-
dous efforts have been devoted to transition-metal-based
asymmetric catalysis because it is one of the most attractive
and practical approaches owing to its high selectivity and
atom-economic nature.[2] This approach usually relies on the
successful design and synthesis of chiral ligands. In this
regard, phosphine-and-nitrogen-containing ligands are ex-
tremely attractive for asymmetric catalysis because they are
easily prepared from readily available amino acids, chiral
amines, or chiral alcohols.[3] Despite the explosive and im-
pressive advances in this field, the design and synthesis of
structurally novel and readily accessible phosphine ligands
for highly efficient and enantioselective transformations re-
mains a formidable challenge.[1–3] This challenge has moti-
vated chemists to search for novel and simple synthetic ap-
proaches to structurally diverse backbones for chiral ligands.
Accordingly, in terms of the importance of palladium cataly-
sis in asymmetric synthesis, the development of novel phos-
phine ligands still needs substantial exploration for highly
enantioselective asymmetric transformations to be more
practical.
In palladium catalysis, the palladium-catalyzed asymmet-
ric allylic alkylation (AAA, also namely the Tsuji–Trost re-
action) is one of the most powerful reactions for construc-
tion of carbon–carbon and carbon–heteroatom bonds.[4] In
this context, although numerous chiral ligands has been re-
ported for regioselective and enantioselective allylic alkyla-
tion with relatively good performance,[4,5] the palladium-cat-
alyzed asymmetric allylic alkylation or etherification (AAE)
of alcohols and 1,3-diphenyl-2-propenyl acetate has not
been widely reported with high levels of enantioselectivity
owing to the mismatch of poor nucleophilicity of alcohols
with respect to chiral metal–ligand complexes.[4a,6] Notably,
in 2008, Chan and co-workers reported a palladium-cata-
lyzed asymmetric allylic etherification of 1,3-diphenyl-2-pro-
penyl acetate with alcohols in moderate to high yields (58–
98%) and good to excellent levels of enantioselectivity (83–
96%ee) by using the (S,pR)-FerroNPS ligand.[7] Meanwhile,
the research groups of Hou, Ding, Fukuzawa, Du, and
others[8] have also demonstrated independently that various
bidentate phosphine or phosphite ligands associated with
palladium centers afford chiral allylic ethers in moderate to
good levels of enantioselectivity and diastereoselectivity.
However, this useful process to provide chiral allylic ethers
still needs substantial improvement in its level of enantiose-
lectivity and chemical yield to be more practical.
Inspired by these studies and encouraged by our recent
findings on multidentate phosphine ligands that promote
highly efficient, enantioselective copper catalysis,[9] we de-
veloped a new class of multidentate and multifunctional
phosphine ligands for palladium catalysis and asymmetric al-
lylic alkylation, including allylic etherification (AAE). In an
effort to develop low-cost, easy-to prepare phosphine li-
gands, we herein report our recent results on the design and
synthesis of a new cyclic tertiary-diamine-containing diphos-
phine ligands having two nitrogen atoms (CycloN2P2-Phos),
a ligand that can be prepared from the very cheap and read-
ily accessible trans-1,2-diaminocyclohexane; we also report
the application of this ligand in the palladium-catalyzed
asymmetric allylic etherification (AAE) of 1,3-diaryl-2-pro-
penyl acetate with alcohols and silanols.
trans-1,2-Diaminocyclohexane is very important chiral
molecule that has been applied widely as the precursor of
organocatalysts or chiral diamine-based ligands in asymmet-
ric catalysis.[10] In this regard, it was anticipated that the syn-
ergy between and Lewis basic nature of two nitrogen centers
of the chiral 1,2-diaminocyclohexane backbone would lead
to catalysts of superior performance in a variety organic
transformations.[11] In addition, chiral trans-1,2-diaminocy-
clohexane is a versatile intermediate for the syntheses of
various phosphine ligands that have been developed previ-
ously by, for example, the research groups of Trost[12] and
Ding,[13] who have contributed greatly to the development
of diamine-based phosphine ligands (Figure 1). Realizing
the power of trans-1,2-diaminocyclohexane-derived phos-
phine ligands when applied in asymmetric catalysis, we de-
signed and synthesized a novel multifunctional phosphine
[a] F. Ye,+ Dr. Z.-J. Zheng,+ Dr. L. Li, Dr. K.-F. Yang, Prof. Dr. L.-W. Xu
Key Laboratory of Organosilicon Chemistry and
Material Technology of Ministry of Education
Hangzhou Normal University, Hangzhou 310012 (P. R. China)
Fax : (+86)571-28865135
[b] Prof. C.-G. Xia, Prof. Dr. L.-W. Xu
State Key Laboratory for Oxo Synthesis and Selective Oxidation
Lanzhou Institute of Chemical Physics (LICP)
Chinese Academy of Sciences (CAS)
Lanzhou, 730000 (P. R. China)
[+] These authors contributed equally to this work
Supporting information for this article is available on the WWW
Figure 1. trans-1,2-Diaminocyclohexane-derived phosphine ligands.
Chem. Eur. J. 2013, 19, 15452 – 15457
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
15453
Ye, Fei
