Boronic acid-mediated ring-opening and Ni-catalyzed arylation of 1-arylcyclopropyl tosylates

Article abstract of DOI:10.1039/d0cc05895e

Herein, we describe a protocol for the ring-opening arylation of 1-arylcyclopropyl tosylates, in which boronic acids promote ring-opening and a Ni catalyst facilitates arylation in high regioselectivity. A number of 2-arylated allyl derivatives are synthesized, which are relevant motifs found in biologically active molecules.

Full text of DOI:10.1039/d0cc05895e

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DOI: 10.1039/D0CC05895E
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Received 00th
January 20xx,
Boronic acid–mediated ring-opening and Ni-catalyzed arylation of
1-arylcyclopropyl tosylates
L. Reginald Mills, John J. Monteith, and Sophie A. L. Rousseaux*
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Figure 1. The 2-substituted allyl motif and synthetic approaches for
its preparation
Herein, we describe a protocol for the ring-opening arylation of 1-
arylcyclopropyl tosylates, in which boronic acids promote ring-
a) Ring-opening of cyclopropyl tosylates
opening and
a Ni catalyst facilitates arylation in high
Kulinkovich;
regioselectivity. A number of 2-arylated allyl derivatives are
synthesized, which are relevant motifs found in biologically active
molecules.
Nu
TsCl
O
acid or cat. TM
TsO
R
Nu
R
R
OR’
DePuy, 1965
Kulinkovich, 2002
Cha, 2007
Cyclopropanols are well established synthetic intermediates
that serve as three-carbon units for accessing a number of valuable
R
products.1
A unique cyclopropanol-derived reagent is the
N
R
OAc
Br
R
Ph
R
cyclopropyl tosylate (Figure 1a), which is readily accessed from an
ester using Kulinkovich chemistry (retrosynthesis arrow), or from
the corresponding ketone using Simmons–Smith chemistry.1 These
intermediates are labile at the C–O bond, and can be activated with
a Brønsted or Lewis acid in the presence of a nucleophile (Nu) to
give the ring-opened, allyl product. An early example of this type of
ring-opening functionalization is the solvolysis of cyclopropyl
tosylates with acetic acid reported by DePuy and coworkers in
1965, which yields the allyl acetate.2,3 Since then, there have been a
number of reports employing cyclopropyl tosylates,1,4,5 including
studies of the mechanism of ring-opening,6 and metal-catalyzed
with MgBr2
with Pd and HNR2
with HOAc
b) This work: Boronic acid–mediated ring-opening functionalization
cat. Ni,
Ar2B(OH)2
Ar2B(OH)2
TsO
Ar1
Ar2
Ar1
Ar1
OTs
Herein, we report the ring-opening functionalization of 1-
arylcyclopropyl tosylates. This process was discovered while we
were exploring related chemistry for the use of cyclopropanols as
C–O electrophiles in a Ni-catalyzed Negishi cross-coupling.10 For this
reaction, the ring-opening is mediated by arylboronic acid
(Ar2B(OH)2), which generates the allyl cation (Figure 1b). The allyl
cation then undergoes Ni-catalyzed cross-coupling with the
arylboronic acid, giving the arylated product.11 Together, this
reactivity is a simple and straightforward way of accessing allyl
derivatives bearing a variety of aryl substituents at the 2-position,
which are valuable synthetic intermediates.12,13 While other
methods for the metal-catalyzed arylation of 2-aryl-substituted allyl
electrophiles exist,14 rapid access to allyl coupling partners is not
always trivial, since they are often synthesized in multiple steps
from esters, ketones, or other oxidized derivatives. Since
cyclopropyl tosylates are directly synthesized from esters or
ketones,1 our strategy offers complementary access to 2-
substituted allyl products.
substitution reactions.7
A different use of the ring-opening
reactivity of cyclopropyl tosylates was reported by Kulinkovich and
coworkers, who discovered that these intermediates can be
converted to the 2-substituted allyl bromide in the presence of
MgBr2.8 Other Lewis acids like MgCl2, TiCl4, and AlCl3 can also
achieve ring-opening to generate the corresponding allyl halide.8
More recently, Cha and coworkers found that 1-alkenylcyclopropyl
tosylates are amenable to ring-opening functionalization with
nucleophiles such as amines in the presence of catalytic Pd.9
However, the scope of this transformation is limited to 1-alkenyl-
substituted cyclopropyl tosylates.
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Journal Name
Table 1. Optimization of the reactiona
number of meta-substituted arylboronic acids weVrieewaAlsrtoiclevOianblinlee
catalyst (10 mol %)
K3PO4 (4 equiv)
DOI: 10.1039/D0CC05895E
(2f–2h). For substrates with labile halogens like
[B]
OMe
TsO
Ph
Table 2. Scope of the reactiona
+
PhMe (0.2 M)
110 ºC, 1 h
NiCl2(PPh3)2
(10 mol %)
MeO
(2 equiv)
Ph
X
X
1a
(1 equiv)
TsO
R1
2a
R2
R2
+
K3PO4 (4 equiv)
PhMe (0.2 M)
110 ºC, 1 h
R1
(HO)2B
(2 equiv)
Yield 2a (%)b
Entry
catalyst
[B]
para:ortho
1
2
(1 equiv)
PdCl2(PPh3)2
NiCl2(PPh3)2
NiCl2(PCy3)2
none
B(OH)2
–
1
22
Arylboronic acids
Me
96 (82)c
82
2a, R = OMe, 82%, >20:1:1 r.r.
2b, R = H, 77%
B(OH)2
B(OH)2
B(OH)2
2
3
4
5
>20:1
>20:1
8.9:1
R
2c, R = CO2Me, 52%, >20:1:1 r.r.
2d, R = Cl, 64%, 19:4.4:1 r.r.b
2e, R = F, 86%, >20:1:1 r.r.
92
Ph
Me
Ph
d
none
33
7.6:1
2f, 55%, 14:1.0:1 r.r.
(ArBO)3
Bnep
F
none
none
–
–
6
7
<5
<5
S
BF3K
Ph
R
Ph
aReactions performed on 0.10-mmol scale. See SI for full details; bGC-MS
yield using n-dodecane as internal standard; cIsolated yield; d0.67 equiv. nep
= neopentylglycol.
Ph
2g, R = OMe, 76%, 11:1:1 r.r.
2h, R = Me, 75%, >20:8.4:1 r.r.
2i, R = F, 89%, >20:1:1 r.r.
2j, 70%, 2.9:1:<1 r.r. 2k, 47%, 8.0:1:<1 r.r.
S
Since some 1-substituted cyclopropyl tosylates can be ring-
opened and functionalized using catalytic Pd,9 we began our
investigation by exploring Pd catalysis to facilitate this reaction
(Table 1). Using 1-phenylcyclopropyl tosylate (1a), 4-
methoxyphenylboronic acid (2 equiv), PdCl2(PPh3)2 (10 mol %),
and K3PO4 (4 equiv), the arylated product (2a) was obtained in
a modest 22% yield (entry 1). Switching the catalyst to
NiCl2(PPh3)2 delivered the product in excellent 96% yield (entry
2). Other Ni catalysts like NiCl2(PCy3)2 were also competent in
this reaction, though performed slightly less efficiently (entry
3) (for other catalysts, see the SI). Intriguingly, the reaction
was still efficient in the absence of catalyst, giving the product
in 92% yield, though with imperfect selectivity for substitution
at the ipso position (entry 4). Arylboronic acids are known to
participate in SEAr chemistry with imperfect regioselectivity,15
suggesting that a similar process may be occurring under these
catalyst-free conditions. Under catalyst-free conditions, we
found that the aryl boroxine (entry 5) was less efficient than
the arylboronic acid, affording product 2a in 33% yield.
Arylboronic esters such as ArBnep (entry 6), as well as
potassium aryl trifluoroborate salts (entry 7), were ineffective
in this transformation. It should also be noted that cyclopropyl
tosylate (1a) is stable at 110 ºC after 1 h, both in the absence
and presence of a Ni catalyst. In the presence of arylboronic
acid at 110 ºC, full conversion of this substrate is achieved
after 1 h.
With these optimized conditions, we next explored the
scope of this reaction (Table 2). Since some arylation is
possible in the absence of a Ni catalyst (Table 1, entry 4),
several entries gave mixtures of regioisomers. However,
reactions in the presence of Ni are generally more
regioselective than those carried out without catalyst. For the
structures drawn, the substitution reflects the regioisomer
obtained after ipso substitution of the boronic acid. The
conditions are compatible with a number of arylboronic acids,
including electron-rich (2a), electron-neutral (2b, 2f), and
electron-deficient (2c–2e, 2j) substrates. Arylboronic acids
with strong para electron-withdrawing groups (4-acetylphenyl,
4-cyanophenyl) gave <20% yield of the desired product. A
O
N
Ph
Ph
Ph
Me
2l, 59%, >20:1:1 r.r.
2m, 63%, >20:1 r.r.
2n, 54%, 18:1 r.r.
Cyclopropanols
OMe
OMe
Ph
2o, 69%, 9.8:1.1:1 r.r.
2p, 62%, 10:1.4:1 r.r.b
OMe
OMe
OMe
F
F
Br
2s, 32%,
5.4:1.0:1 r.r.b
2q, 78%,
>20:1:1 r.r.
2r, 52%,
8.4:1:<1 r.r.b
aReactions performed on 0.20–0.40 mmol scale. Yields are isolated and the
combination of regioisomers. Regioisomer ratios were determined by GC-
MS analysis of the crude reaction mixture. The structures drawn reflect the
regioisomer obtained after ipso substitution of the arylboronic acid.
bReaction performed without NiCl2(PPh3)2; for yields with and without Ni,
see SI.
chlorides (2d), the reaction performed better in the absence of
a Ni catalyst; in the presence of Ni, products resulting from
halide functionalization (reduction, arylation) were detected
by GC-MS. The compatibility of electron-withdrawing groups
(2c) is complementary to related Friedel–Crafts chemistry of
activated cyclopropanols using electron-rich arenes.11
For this Ni-catalyzed process, the regioselectivity with
respect to arylboronic acid functionalization with both
electron-donating and -withdrawing groups is dictated by the
position of the boronic acid and not the inherent reactivity
expected for SEAr chemistry (e.g. ortho and para for 2f–2i;
meta for 2c). Employing electron-deficient substrates (e.g. 2c)
in the absence of catalytic Ni gave low yields (<10%). A number
of electron-rich heteroaromatic boronic acids are also
compatible with the chemistry (2k–2n). For heteroaromatic
boronic acids with rings that could participate in Friedel–Crafts
chemistry (e.g., 2k, 2l), substitution was only detected on the
boronic acid–containing ring.
A number of 1-arylcyclopropyl tosylates are compatible
with the chemistry, including electron-neutral (2o, 2p) and
2 | J. Name., 2012, 00, 1-3
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electron-deficient (2q–2s) substrates.16 Ortho-substituted 1- Figure 2. Mechanistic experiments
arylcyclopropyl tosylates (2r, 2s) afforded the desired product
View Article Online
DOI: 10.1039/D0CC05895E
a) Regioselectivity without and with Ni
3-OMePhB(OH)2 (2 equiv)
K3PO4 (4 equiv), catalyst
in higher yield in the absence of Ni catalyst (for yields and
TsO
selectivity in the presence of catalytic Ni, see the SI).
Ph
1a
PhMe
110 ºC, 1 h
Ph
OMe
Cyclopropyl tosylates without 1-aryl substituents gave very
little conversion under standard conditions, both in the
presence and absence of NiCl2(PPh3)2. The low yields for some
substrates may be due to decomposition of the cyclopropyl
tosylate (1) at the reaction temperature (110 °C).
Next, mechanistic experiments were performed to better
understand i) the mechanism of the background Ni-free
arylation reaction and ii) the role of the boronic acid in this
2g
(1 equiv)
m:p:o
Entry
Catalyst (10 mol %)
GC-MS Yield (%)
NiCl2(PPh3)2
none
91
41
1
2
11 : 1 : 1
1 : 2.9 : 2.3
b) Arylboronic acid competition
X
background process (Figure 2). First,
a head-to-head
B(OH)2
comparison was made for the reaction of 3-
methoxyphenylboronic acid with and without a Ni catalyst
(Figure 2a). In the presence of 10 mol % NiCl2(PPh3)2 (entry 1),
product 2g was obtained in 91% GC-MS yield and 11:1:1
selectivity for functionalization at the ipso position. The
predominant formation of this regioisomer is consistent with
transmetallation of 3-methoxyphenylboronic acid to Ni.
Alternatively, in the absence of Ni (entry 2), the product was
obtained in only 41% GC-MS yield, with the major
regioisomers instead being those resulting from substitution
para and ortho to the electron-donating methoxy substituent.
This result is consistent with an SEAr mechanism for the Ni-free
background process. It also suggests that the arylboronic acid
is likely responsible for cyclopropane ring-opening to generate
the allyl cation intermediate.
Ph
X
K3PO4 (2.4 equiv)
2-X
+
TsO
Ph
(1.1 equiv)
+
PhMe
110 ºC, 1 h
1a
(1 equiv)
Ph
PhB(OH)2
(1.1 equiv)
Ph
2b
1
OMe
0.5
0
t-Bu
Ph
Cl
Br
-0.5
-1
CO2Me
F
y = -1.8379x - 0.0101
R² = 0.763
-1.5
To better understand the Ni-free background reaction,
competition experiments were performed between 4-
substituted arylboronic acids (1.1 equiv) and phenylboronic
acid (1.1 equiv). The product distribution between the 4-
substituted aryl product (2-X) and the phenyl product (2b) was
evaluated (Figure 2b). When the log(2-X/2b) was taken and
plotted according to σpara of 2-X, a negative linear relationship
was obtained, consistent with build-up of positive charge in
the product-determining step. This finding is consistent with
an SEAr mechanism to yield the arylated product in the
absence of Ni catalyst. It should be noted that in this
experiment any electronic effects which promote boronic
acid–mediated ring-opening of 1a cannot be excluded.
To further confirm the role of the arylboronic acid in ring-
opening of the cyclopropyl tosylate, we investigated whether
other nucleophiles could be used to trap an allyl cation
generated from 1a using PhB(OH)2 (Figure 2c). In the presence
of substoichiometric amounts of phenylboronic acid (40 mol
%) and K3PO4, 1-phenylcyclopropyl tosylate 1a underwent
trapping with a range of nucleophiles (3) to yield the allyl
product, 4. Viable nucleophiles include thiol (3a), phenol
(3b),17 and pyrazole (3c).18
CN
-2
-0.4
-0.2
0
0.2
σpara
0.4
0.6
c) Allyl cation probe: Substitution with other nucleophiles
PhB(OH)2 (40 mol %)
K3PO4 (4 equiv)
TsO
+
Nu
H
Nu
Ph
1a
PhMe, 110 ºC, 1 h
Ph
3
(2 equiv)
4
(1 equiv)
N
Me
HS
HN
HO
OMe
3b, 40%
3a, 57%
3c, 38%
d) Ring-opening of a bicyclic cyclopropyl tosylate
H
2
K3PO4
(4 equiv)
2
OMe
3
1
Ar
+
1
PhMe (0.2 M)
110 ºC, 1 h
3
OTs
(HO)2B
1b
(1 equiv)
(2 equiv)
2t, 50%, 7.9:1:<1 r.r.
>20:1 C2–C3
Ar = 4-OMePh
obtained (2t) was that resulting from C2–C3 cleavage, with
retention of the cis relationship between the 1-position and 2-
position substituents. This result is consistent with
conventional selectivity for SN1 reactions of cyclopropyl
electrophiles, which are known to undergo concerted,
Finally, we examined whether the arylboronic acid–
mediated cyclopropyl tosylate ring-opening was consistent
with known regio- and stereoselectivity for acid-catalyzed ring-
openings of cyclopropanol derivatives. Thus,
a bicyclic
cyclopropyl tosylate (1b) was exposed to the reaction
conditions in the absence of Ni (Figure 2d). The product
disrotatory C2–C3 ring-opening to generate the allyl cation.
5,6,19
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J. Name., 2013, 00, 1-3 | 3
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Journal Name
1
(a) O. G. Kulinkovich. Chem. Rev. 2003, 103, 259V7ie;w(bA)rtiAcl.e Online
Nikolaev, A. Orellana. Synthesis 2016, D4O8,I:11704.110–391/7D608C;C(0c5)8L9.5E
R. Mills, S. A. L. Rousseaux. Eur. J. Org. Chem. 2019, 8.
C. H. DePuy, L. G. Schnack, J. W. Hausser, W. Wiedemann. J.
Am. Chem. Soc. 1965, 87, 4006.
For the ring-opening of cyclopropyl tosylate: J. D. Roberts, V.
C. Chambers. J. Am. Chem. Soc. 1951, 73, 5034.
(a) B. A. Howell, J. G. Jewett. J. Am. Chem. Soc. 1971, 93, 798;
(b) J. Salaün, J. Org. Chem. 1976, 41, 1237.
D. H. Gibson, C. H. DePuy, Chem. Rev. 1974, 74, 605.
(a) J. W. Hausser, N. J. Pinkowski. J. Am. Chem. Soc. 1967, 89,
6981; (b) P. v. R. Schleyer, W. F. Sliwinski, G. W. Van Dine, U.
Schöllkopf, J. Paust, K. Fellenberger. J. Am. Chem. Soc. 1972,
94, 125.
(a) A. Stolle, J. Salaün, A. de Meijere. Tetrahedron Lett. 1990,
31, 4593; (b) P. Aufranc, J. Ollivier, A. Stolle, C. Bremer, M.
Es-Sayed, A. de Meijere, J. Salaün, Tetrahedron Lett. 1993,
34, 4193; (c) S. Racouchot, J. Ollivier, J. Salaün, Synlett 2000,
1729; (d) F. Lecornué, F. Charnay-Pouget, J. Ollivier. Synlett
2006, 1407.
A proposed mechanistic picture for this cyclopropyl
tosylate ring-opening arylation is outlined in Figure 3. Starting
with 1-arylcyclopropyl tosylates (1), activation of the substrate
occurs with arylboronic acid, which likely acts as an H-bond
donor (5).20 This intermediate then fragments to release
tosylate anion and allyl cation 6. In the absence of Ni, this
cation can be trapped with an activated arylboronate to yield
Wheland intermediate 7. Elimination of the boronate restores
aromaticity, forming arylated product 2. Alternatively, in the
presence of Ni(0), oxidative addition can yield Ni(II)
intermediate 8, which can undergo transmetallation with
arylboronic acid to yield intermediate 9. Finally, reductive
elimination releases the allyl arene 2. In the presence of Ni, it
is likely that some of the non-Ni-catalyzed process also occurs,
which explains the imperfect regioselectivity for certain entries
in Table 2.
2
3
4
5
6
7
Figure 3. Proposed mechanisms without and with Ni
8
9
(a) Y. Y. Kozyrkov, O. G. Kulinkovich. Synlett 2002, 443; (b) O.
G. Kulinkovich, Y. Y. Kozyrkov, A. V. Bekish, E. A.
Matiushenkov, I. L. Lysenko. Synthesis 2004, 1713.
L. G. Quan, H. G. Lee, J. K. Cha. Org. Lett. 2007, 9, 4439.
p-Tol
H
H
O
O
O
Ar2B(OH)2
Ar2
B
Ar1
S
Ar1
–TsO–
O
O
OTs
Ar1
6
1
5
10 L. R. Mills, J. J. Monteith, G. d. Passos Gomes, A. Aspuru-Guzik,
S. A. L. Rousseaux. J. Am. Chem. Soc. 2020, 2020, 142, 13246–
13254.
11 For a related SEAr functionalization reaction of silyl-protected
cyclopropanols using electron-rich arenes and
diethylaminosulfur trifluoride (DAST) to generate the allyl
cation, see M. Kirihara, T. Noguchi, H. Kakuda, T. Akimoto, A.
Shimajiri, M. Morishita, A. Hatano, Y. Hirai. Tetrahedron Lett.
2006, 47, 3777–3780.
12 A. A. Protter, S. Chakravarty. Compounds and Methods of
Treating Hypertension. WO Patent 2012112961, Aug. 23,
2012.
13 C. S. Burgey, D. V. Paone, A. Q. Shaw, J. Z. Deng, D. N.
Nguyen, C. M. Potteiger, S. L. Graham, J. P. Vacca, T. M.
Williams. Org. Lett. 2008, 10, 3235.
14 For select recent metal-catalyzed reactions employing 2-
substituted allyl electrophiles: (a) C. Dong, L. Zhang, X. Xue, H.
Li, Z. Yu, W. Tang, L. Xu RSC Adv. 2014, 4, 11152; (b) X. Cui, S.
Wang, Y. Zhang, W. Deng, Q. Qian, H. Gong. Org. Biomol. Chem.
2013, 11, 3094; (c) M. D. Levin, F. D. Toste, Angew. Chem. Int.
Ed. 2014, 53, 6211; (d) X.-G. Jia, P. Guo, J. Duan, X.-Z. Shu.
Chem. Sci. 2018, 9, 640.
R
without Ni
Ar2B(OH)2
K3PO4
Ar2
Ar1
Ar1
B(OR)3
2
7
with Ni
–Ni(0)
Ar2B(OH)2
K3PO4
Ln
NiII
Ar2
Ni(0)
Ar1
Ar1
NiIIXLn
8
9
In conclusion, we have discovered an arylboronic acid-
mediated and Ni-catalyzed process for the ring-opening
arylation of 1-arylcyclopropyl tosylates, which are readily
accessible from esters via the Kulinkovich reaction. The
arylboronic acid plays two roles in this reaction: i) it enables
cyclopropane ring-opening and ii), it participates in a Ni-
catalyzed cross-coupling to yield allyl products bearing aryl
substituents at the 2 position.
We thank NSERC (Discovery Grants and Canada Research
Chair programs), the Canada Foundation for Innovation
(Project No. 35261), the Ontario Research Fund, Kennarshore
Inc., and the University of Toronto for generous financial
support of this work. We also acknowledge the Canada
Foundation for Innovation (Project No. 19119) and the Ontario
Research Fund for funding the Centre for Spectroscopic
Investigation of Complex Organic Molecules and Polymers. L.
R. M. thanks NSERC for a graduate scholarship (PGS-D). J. J. M.
thanks NSERC for a graduate scholarship (CGS M) and the
University of Toronto for a doctoral scholarship (FAST).
15 G. Wu, S. Xu, Y. Deng, C. Wu, X. Zhao, W. Ji, Y. Zhang, J.
Wang. Tetrahedron 2016, 72, 8022–8030.
16 In our hands, electron-rich 1-(hetero)arylcyclopropyl
tosylates (e.g., 1-(4-methoxyphenyl), 1-(2-thienyl), 1-(2-
furanyl)) were difficult to access.
17 The reaction with phenol 3b gave the O-allylated product.
18 Adding catalytic NiCl2(PPh3)2 to these reactions gave no
noticeable increase in yield. Nucleophilic arenes that
typically participate efficiently in Friedel–Crafts chemistry
(e.g. 1H-indole, 1,3,5-trimethoxybenzene) yielded no
detectable amount of substituted product.
19 Alabugin, I. V. Stereoelectronic Effects. Chichester, UK;
Hoboken, NJ: John Wiley & Sons, 2016.
20 (a) K. M. Diemoz, A. K. Franz. J. Org. Chem. 2019, 84, 1126;
(b) S. Zhang, D. Lebœuf, J. Moran. Chem. Eur. J. 2020, 26,
9883.
Conflicts of interest
The authors declare no conflicts of interest.
Notes and references
4 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/D0CC05895E
We describe a procedure for the ring-opening and arylation of 1-arylcyclopropyltosylates to yield
2-susbtituted allyl products using boronic acids and Ni catalysis.