DOI: 10.1002/chem.201702824
Communication
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Mechanistic Investigations
Catalytic Functionalization of Styrenyl Epoxides via
[a]
demonstrated the oxidative addition of a different low-valent
Abstract: Low-valent nickel is shown to preferentially iso-
merize mono- or disubstituted epoxides into their corre-
sponding aldehydes. Experiments with tetrasubstituted
epoxides demonstrate that these reactions proceed via re-
active 2-nickelaoxetane intermediates, and that the oxida-
tive addition step likely occurs with retention of configura-
tion. The monosubstituted aldehyde isomerization prod-
ucts were found to rapidly react with HBpin to form boro-
nate esters. These hydroboration reactions could be per-
formed catalytically.
2
2
nickel source, [(dtbpe)Ni] (m-h :h -C H ) 1 (dtbpe=1,2-bis{di-
2
6
6
[8]
tert-butyl}phosphinoethane), into the CÀO bond of epoxides
Scheme 1, bottom). Notably, the oxidative addition to form 2
(
occurs with retention of configuration, in contrast with Hill-
[5]
house’s synthesis of azanickelacyclobutanes (Scheme 1, top)
[7a,b]
and Jamison’s reductive coupling strategy,
occur with inversion of configuration.
both of which
2-Metallaheterocyclobutanes are an unusual structural motif
that have frequently been invoked as reactive intermediates
during organometallic transformations, yet well-defined exam-
[
1]
ples have been only recently reported. Ongoing research in
our group has been focused on exploring the development of
new catalytic transformations that feature these metallahetero-
[
2]
cycles as intermediates. Key to achieving such processes is to
develop an understanding of the fundamental reactivity of
these complexes. As such, we have demonstrated that 2-rho-
daoxetanes undergo transmetallation with aryl-and alkenylbor-
Scheme 1. Synthesis of nickelaheterocyclobutanes from nickel(0).
[
3]
onic acids, and ring expansion with various other organic
Doyle and co-workers have recently reported nickel-cata-
[
4]
[9]
electrophiles. More recently, we have become interested in
exploring the feasibility of substituting a cheaper, more earth-
abundant metal, such as nickel, for rhodium. This is appealing
not only for economic reasons, but also because it could lead
to complementary reactivity of these nickelaheterocycles from
their rhodium counterparts.
lyzed cross-coupling of styrenyl epoxides with boronic acids.
The authors propose that catalysis occurs through a tandem
process: first, the isomerization of the epoxide to the corre-
sponding aldehyde via a nickelaoxetane intermediate, followed
by a 1,2-arylation to give the final product. Both of these
cycles are proposed to be catalyzed by nickel(0). We were thus
intrigued to explore the reactivity of 1 towards styrenyl epox-
ides. We report herein that 1 can rapidly isomerize styrenyl ep-
oxides preferentially to their corresponding aldehydes via nick-
elaoxetane intermediates, that the oxidative addition step
occurs with retention of configuration, and that the aldehyde
complexes can undergo catalytic hydroboration with HBpin,
demonstrating proof-of-concept that these reactions can be
applied towards catalysis.
In particular, Hillhouse has demonstrated that (bpy)Ni(COD)
(
bpy=2,2’-bipyridyl, COD=1,5-cyclooctadiene) can oxidatively
[
5]
[6]
add to both aziridines and thiiranes to generate the corre-
sponding nickelaheterocyclobutanes. The Jamison group has
also invoked the formation of nickelaoxetanes through an S 2-
N
type oxidative addition of nickel(0) during the catalytic reduc-
[
7]
tive coupling of epoxides and alkynes. Our group has since
Addition of styrene oxide 3 to an orange–red solution of 1
[
a] Dr. A. N. Desnoyer, J. Geng, Dr. M. W. Drover, Dr. B. O. Patrick,
Prof. Dr. J. A. Love
Department of Chemistry
in C D results in the formation of a mixture of products as de-
6
6
31
1
termined by P{ H} NMR spectroscopy (Scheme 2). The major
The University of British Columbia
product, formed in 73% yield, displays two doublets at 94.6
2
036 Main Mall, Vancouver, BC, V6T 1Z1 (Canada)
2
and 83.9 ppm that show large J values of 74 Hz, indicative
P,P
E-mail: jenlove@chem.ubc.ca
of an asymmetric coordination geometry at
a nickel(0)
[10]
1
centre. The minor product (12% yield by H NMR spectrosco-
py) displays similar spectroscopic features, that is, two [AB]
Chem. Eur. J. 2017, 23, 1 – 5
1
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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