Copper-catalyzed O-arylation of N-protected 1,2-aminoalcohols using functionalized trivalent organobismuth reagents

Article abstract of DOI:10.1039/c4ob02497d

The O-arylation of 1,2-aminoalcohols using functionalized triarylbismuth reagents is reported. The reaction can be performed using substoichiometric amounts of copper acetate and operates under mild conditions. Good functional group tolerance is observed, giving access to a range of β-aryloxyamines. The effect provided by the amino group in the arylation reaction is investigated.

Full text of DOI:10.1039/c4ob02497d

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Journal Name
RSCPublishing
COMMUNICATION
Copper-Catalyzed O-Arylation of N-Protected 1,2-
Aminoalcohols Using Functionalized Trivalent
Organobismuth Reagents
Cite this: DOI: 10.1039/x0xx00000x
Pauline Petiot,a Julien Dansereau,a Martin Hébert,a Imene Khene,a Tabinda Ahmad,a
Samira Samaali,a Maxime Leroy,a Francis Pinsonneault,a Claude Y. Legault*b and
Alexandre Gagnon*a
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
www.rsc.org/
O
The O-arylation of 1,2-aminoalcohols using functionalized
triarylbismuth reagents is reported. The reaction can be
performed using substoichiometric amounts of copper
acetate and operates under mild conditions. Good
functional group tolerance is observed, giving access to a
range of β-aryloxyamines. The effect provided by the amino
group in the arylation reaction is investigated.
OH
H
O
H
HN
9
)
(
R =
R =
O
OH
OH
O
OH
OH
Shishididemniol A (1)
NH2
NH2
HO
HN
OH
Shishididemniol
natural product
O
( )
9
OH
Cl
OH
Shishididemniol B (2)
O
R
OH
O
NH2
O
F
O
N
HN
β-Aryloxyamines are frequently found in natural products and in
medicinally relevant compounds. For example, this moiety has been
identified in shishididemniol A (1) and B (2), two natural products
extracted from a tunicate of the family Didemnidae (Figure 1).1
Rosiglitazone (3), an antidiabetic drug, Ulimorelin (TZP-101, 4),2 a
ghrelin inhibitor that has advanced into phase-III clinical studies, and
O
O
O
S
N
N
NH
HN
HN
Me
Mexiletine (Mexitil, 5)
Antiarrhythmic agent
O
O
Rosiglitazone (Avandia, 3)
Antidiabetic drug
N
N
Ulimorelin (TZP-101) (4)
Ghrelin receptor agonist
MeO2S
Me
Mexiletine (5), an antiarrhytmic drug, also contain
a β-
N
O
O
O
aryloxyamine. The importance of 1,2-aryloxyamines in drug
discovery can be further exemplified with compounds 6-10 which
are inhibitors of various biological targets for which advanced
profiling has been performed.3,4,5,6,7
N
HO
R
NH
O
O
O
R
NH
O
HN
OH
N
CF3
β-Aryloxyamines can be accessed through SNAr reactions between
1,2-aminoalcohols and electron poor aryl halides.8 Alternatively,
these compounds can also be prepared from the same precursors
through the addition of phenols using Mitsunobu conditions9 or via
SN2 reactions on the corresponding mesylates or tosylates.10 Even
though these approaches are widely spread in the pharmaceutical
industry, they are not free of limitations as they require the presence
of electron withdrawing groups on the aryl unit (SNAr), necessitate
the derivatization of the alcohol (SN2) or lead to the formation of
side products that can complicate the isolation of the desired product
(i.e. phosphine oxide and urea in the Mitsunobu reaction).
N
HDAC inhibitor (7)
(8)
HCV NS5B
polymerase inhibitor
O
!-secretase inhibitor
R = Ph (6a)
R = i-Bu (6b)
CO2H
H
N
O
F
F
O
H
N
N
N
N
H
Cl
O
O
O
O
DG-051 (9)
(10)
PDK1 inhibitor
Leukotriene A4 hydrolase
inhibitor of leukotrine B4
synthesis
Fig. 1. Selected examples of β-aryloxyamines in natural products,
drugs, and medicinal chemistry compounds.
The copper-catalyzed O-arylation of 1,2-aminoalcohols using aryl
halides, as illustrated by the pioneering work of Buchwald11 and
Evano,12 constitutes a highly efficient strategy for the preparation of
β-aryloxyamines.13,14,15 Surprisingly, the O-arylation of 1,2-
aminoalcohols using arylmetals has been considerably less studied
and to the best of our knowledge, the only example using this
approach involved tetraphenylbismuth fluoride as the arylating
source.16
We reported over the past few years a portfolio of C–C, C–N, and
C–O bond forming reactions involving organobismuth reagents.17
Organobismuthanes are an attractive class of organometallic
reagents that can be easily prepared from inexpensive and non-toxic
bismuth salts.18 Triarylbismuthanes are air and moisture stable and
can be purified by simple silica gel chromatography. In addition,
organobismuthanes show remarkable functional group tolerance,
making them ideal candidates for the development of methodologies
oriented towards medicinal chemistry applications.
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We recently disclosed
a general copper-catalyzed N-arylation dichloromethane (entry 7). We next directed our efforts towards
reaction of azoles and diazoles using triarylbismuth reagents.17a In lowering the catalyst loading and found a moderate reduction in the
the course of our studies, we found that the arylation of the yield of the arylation process upon using 0.3 equivalent of copper
hydroxypropylindole 11 using tris-meta-(methylphenyl)bismuthane acetate (entry 8). In addition, reducing the reaction time to 6 hours
proceeded exclusively on the indole to afford 12, suggesting that an instead of overnight provided the desired compound in similar yield
alcohol cannot be arylated under these conditions (Scheme 1). (entry 9). Finally, a good yield could be obtained under catalytic
However, when the N-BOC-tryptophanol derivative 13 was conditions by conducting the reaction in toluene at 80 ˚C overnight
submitted to the same conditions, the product of bis-arylation 14 was (entry 10).
isolated in moderate yield, suggesting that the amino group activates
the alcohol towards the arylation. Moreover, the yield of this Table 1 Optimization of the conditions for the O-arylation of N-
reaction could be greatly improved by using 2.0 equivalents of the
bismuth reagent.
BOC-D-α-phenylglycinol 15.
O
O
O
NH
O
NH
Ph3Bi (1.0 equiv)
Pyridine (3.0 equiv)
OH
O
OH
OH
Cu(OAc)2 (1.0 equiv)
Pyridine (3.0 equiv)
Cu(OAc)2 (1.0 equiv)
CH2Cl2, 50˚C, O2, 16h
"standard conditions"
15
16
CH2Cl2, 50˚C, O2, 12h
(m-MeC6H4)3Bi (1.0 equiv)
N
N
11
H
12 (52%)
Entry Change from "standard conditions"
Yield
(%)a
73
49
51
Me
• selective N-arylation
1
2
3
No change
Ambient air instead of oxygen
0.7 equiv Ph3Bi instead of 1.0
Et3N instead of pyridine
NHBOC
OH
NHBOC
O
Cu(OAc)2 (1.0 equiv)
Pyridine (3.0 equiv)
CH2Cl2, 50˚C, O2, 12h
4
73
Me
5
6
7
K2CO3 instead of pyridine
1.2 equiv pyridine instead of 3.0
Toluene instead of CH2Cl2
0.3 equiv Cu(OAc)2 instead of 1.0
0.3 equiv Cu(OAc)2 and 6h instead of o.n.
0.3 equiv Cu(OAc)2 in toluene at 80˚C
31
67
76
62
58
71
(m-MeC6H4)3Bi (1.0 equiv): 52%
(m-MeC6H4)3Bi (2.0 equiv): 80%
N
N
H
13
14
Me
8b
9b
10b
• N,O-diarylation
Scheme 1 N- vs O-Arylation of 3-(3-hydroxypropyl)-1H-indole 11
and N-BOC-tryptophanol 13.
a Isolated yield of pure product 16. b 1.2 equiv pyridine.
David and Thieffry reported in 1983 the effect of neighbouring
hydroxylic groups on the arylation reaction of alcohols using
triphenylbismuth diacetate but never explored the ability of nitrogen
moieties in influencing this transformation.19 In 1986, Barton briefly
studied the arylation of ethanolamine using Ph3Bi(OAc)2 and
obtained a complex mixture of N-, N,N-, and N,O-arylation
products.20 These two reactions relied on pentavalent organobismuth
reagents, which are usually less stable and more tedious to prepare
than their trivalent counterparts. To our knowledge, the only
example of O-arylation of alcohols using a trivalent bismuth reagent
was reported in 1999 by Sheppard and required the use of oxone as a
stoichiometric oxidizing agent.21 We would like to report herein our
study on the O-arylation of 1,2-aminoalcohols using functionalized
triarylbismuthanes and our investigation into the accelerating effect
provided by the amino group.
The ability of other amine protecting groups in enhancing the
reactivity of the alcohol towards arylation was then explored
(Scheme 2). Performing the reaction directly on the unprotected
phenylglycinol afforded the N,O-diaryl product 18a, indicating that
the amino group must imperatively be protected to prevent the
undesired N-arylation pathway.
A survey of different amine
protecting groups demonstrated that a benzyloxycarbonyl group
(18b) and a sulfonyl (18c) give slightly higher yields of the desired
O-aryl product than an acetyl (18d).
PG
PG
Ph3Bi (1.0 equiv)
Pyridine (3.0 equiv)
NH
NH
OH
O
Cu(OAc)2 (1.0 equiv)
CH2Cl2, 50˚C, O2, o.n.
18
17a (PG = H)
17b (PG = Cbz)
17c (PG = Ts)
17d (PG = Ac)
We began by optimizing the reaction conditions for the arylation of
(–)-N-BOC-D-α-phenylglycinol 15, a 1,2-aminoalcohol that does
not possess an indolic scaffold. When this substrate was submitted to
our previously identified conditions,17a the corresponding O-phenyl
product 16 was isolated in 73% yield (Table 1, entry 1). Conducting
the reaction under air led to a considerable reduction in the yield of
the reaction, thus confirming the importance of the oxygen in this
process (entry 2). To evaluate the transferability of the second aryl
group from the triarylbismuthane, we next performed the reaction
using 0.7 equivalent of triphenylbismuth and observed a substantial
drop in the yield of 16, demonstrating that only one aryl group can
be transferred from the triarylbismuthane (entry 3). This
phenomenon is well known in copper-catalyzed reactions involving
organobismuth reagents17a,b and efforts to overcome this issue are in
progress in our group. A rapid screen of different bases showed that
pyridine can be replaced by triethylamine (entry 4) but not potassium
carbonate (entry 5). Our studies also demonstrate that 1.2
equivalents of pyridine are sufficient to obtain an optimal yield of
the arylated product (entry 6). A survey of different solvents led to
the identification of toluene as the most efficient replacement for
O
H
N
BnO
NH
O
O
18a (62%)
18b (80%)
O
O
O
S
p-Tol
NH
O
Me
NH
O
18c (77%)
18d (71%)
Scheme 2 Impact of the protecting group on the arylation of N-
protected phenylglycinol derivatives. PG = Protecting Group.
The scope of the reaction was then investigated by coupling different
functionalized triarylbismuthanes with various 1,2-aminoalcohols
(Scheme
3).
The
tert-butyloxycarbonyl
(BOC)
or
benzyloxycarbonyl (Cbz) protecting groups were selected for its ease
of installation and removal. The organobismuth reagents were
synthesized according to procedures that we reported previously17a,b,d
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and the protocols involving catalytic (Table 1, entry 10: conditions We then turned our attention to substrates where the phenyl group of
A) and stoichiometric (Table 1, entry 1: conditions B) amount of phenylglycinol is substituted or replaced by an alkyl group. For
copper acetate were utilized. As expected, the introduction of a instance, the para-ethoxy and ortho-methoxy derivatives 21i and 21j
methyl group at the para position of the triarylbismuthane had little were obtained in moderate yields using this protocol. To our
impact on the arylation process and afforded the corresponding O- surprise, the insertion of a methylene unit between the phenyl group
aryl product 21a in a reasonable yield using either conditions A or B. and the aminoalcohol segment led to an unexpected drop in the yield
The transfer of an aryl group bearing an electron-withdrawing group
such as a fluorine atom at the para position proceeded equally well,
providing compound 21b in 72% yield under conditions B.
However, introducing an electron-donating group such as a methoxy
at the para position led to a considerable drop in the efficiency of the
process, as indicated by compound 21c. The reaction also proved to
be very sensitive to steric hindrance, as shown by compound 21d
where a methyl group is present at the ortho position of the aryl
group being transferred. This phenomenon is not unprecedented and
was observed previously in the context of our studies on the copper-
catalyzed N-arylation of indoles17a and phenols.17b Unexpectedly, the
effect of the ortho methyl group in the arylation reaction was found
to be much higher with alcohols than with azoles and phenols. Next,
we investigated the transfer of an aryl fragment possessing a
diethylacetal and a trifluoromethyl group at the meta position and
obtained the corresponding O-arylated products 21e and 21f in
modest yields. Surprisingly, a much lower yield was observed when
tris(3-formylphenyl)bismuth was utilized as the arylating agent, as
indicated by compound 21g. This is a sharp contrast to the results
that we obtained with this organobismuthane in the arylation of
azoles17a and phenols17b where the corresponding arylated products
were obtained in excellent yields. The transfer of a phenyl group
bearing an α,β-unsaturated ester at the meta position proved more
efficient, affording compound 21h in 70% yield under conditions A.
of the reaction (21a→21k). Interestingly, products 21l and 21m
where the phenyl group is replaced by a cyclohexyl or an iso-butyl
moiety were successfully prepared using this method. Lastly, the
arylation could also be performed on a secondary alcohol, as
demonstrated by compound 21n.
In order to understand the role of the amino group in the arylation
process, we performed a series of control experiments where specific
geometric and functional modifications are introduced in the
substrate. We first hypothesized that the NHBOC function could be
promoting the O-arylation reaction through complexation of the
copper species via the carbonyl moiety of the carbamate. To test this
hypothesis, we compared the reactivity of the cis- and trans-N-BOC-
indanol derivatives cis-22 and trans-22 using conditions B (Scheme
4). In the event, a higher yield was observed for the trans
stereoisomer, suggesting that the accelerating effect provided by the
amino group is not a result of a complexation of metallic
intermediates by the carbonyl group.
NHBOC
OH
NHBOC
O
cis-22
cis-23 (52%)
Ph3Bi (1.0 equiv)
Pyridine (3.0 equiv)
Cu(OAc)2 (1.0 equiv)
CH2Cl2, 50˚C, O2, o.n.
NHBOC
OH
NHBOC
O
NHBOC
conditions a
NHBOC
OH
FG
trans-22
trans-23 (69%)
O
+
Bi
R
FG
R
3
Scheme 4 Study of the effect of the conformational effect in the O-
arylation of N-BOC-1-amino-2-indanol 22.
19
21
20
NHBOC
NHBOC
O
O
To further investigate the hypothesis that the C=O bond of the
carbamate could be directing the reaction through complexation of
the copper species, we compared the reactivity of the N-benzoyl and
N-benzyl derivatives 24a and 24b of phenylglycinol in the arylation
reaction (Scheme 5). Should there be a complexation involved, it
would be reasonable to expect a much greater yield with the benzoyl
compound 24a than with the benzyl analogue 24b. To our surprise,
similar yields of the O-aryl products were obtained with both
derivatives, thus invalidating our complexation hypothesis.
R
21a (R = Me) 21b (R = F) 21c (R = OMe)
21d
36% (A)
27% (B)
68% (A)
62% (B)
69% (A)
72% (B)
53% (A)
38% (B)
NHBOC
O
NHBOC
O
O
R
H
21g
25% (A)
27% (B)
21e (R = CH(OEt)2) 21f (R = CF3)
57% (A)
56% (B)
42% (A)
40% (B)
NHBOC
NHBOC
O
O
CO2Et
X
X
R
H
Ph
N
Ph
NH
21i (R = p-OEt) 21j (R = o-OMe)
38% (A)
40% (B)
21h
70% (A)
54% (B)
Ph3Bi (1.0 equiv)
Pyridine (3.0 equiv)
38% (B)
OH
O
Cu(OAc)2 (1.0 equiv)
CH2Cl2, 50˚C, O2, o.n.
NHBOC
O
NHBOC
24a (X = O)
24b (X = H,H)
25a (X = O; 68%)
25b (X = H,H; 64%)
O
21l
45% (A)
60% (B)
21k
48% (A)
44% (B)
Scheme 5 Comparison of N-benzoyl 24a and N-benzyl 24b
protecting group in the copper-catalyzed arylation of N-protected
phenylglycinol.
NHBOC
O
O
BOC
N
We then hypothesized that the amide N–H bond could be responsible
for the acceleration of the arylation reaction through formation of
copper species where the amide acts as a ligand. To test this
hypothesis, we performed the arylation reaction using the N-methyl
derivatives 26a and 26b and observed a good conversion to the
corresponding O-aryl products 27a,b, thus discrediting this second
hypothesis (Scheme 6).
21m
49% (A)
23% (B)
21n
50% (A)
52% (B)
Scheme 3 O-Arylation of 1,2-aminoalcohols using functionalized
organobismuthanes. a Conditions A: Ar3Bi (1.0 equiv), pyridine (1.2
equiv), Cu(OAc)2 (0.3 equiv), toluene, 80˚C, O2, o.n.; Conditions B:
Ar3Bi (1.0 equiv), pyridine (3.0 equiv), Cu(OAc)2 (1.0 equiv),
CH2Cl2, 50˚C, O2, o.n.
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30. These values are in line with the relative reactivities illustrated in
Schemes 8 and 9, thus supporting the inductive effect hypothesis.
R
Me
R
Me
N
N
Ph3Bi (1.0 equiv)
Pyridine (3.0 equiv)
OH
O
Cu(OAc)2 (1.0 equiv)
CH2Cl2, 50˚C, O2, o.n.
26a (R = BOC)
26b (R = Me)
27a (R = BOC; 66%)
27b (R = Me; 73%)
NHBOC
OH
NHBOC
O
Scheme
6 Arylation of N-BOC-N-methyl and N,N-dimethyl
phenylglycinol derivatives 26a and 26b.
16
15 (1.0 equiv)
Ph3Bi (1.0 equiv)
Pyridine (3.0 equiv)
ratio 16 : 31 = 1.1 : 1
In order to better evaluate the importance of the amino group in the
reaction, we then performed the arylation on phenethylalcohol 28b, a
simple alcohol with no amino group and observed a 30% drop in the
yield of the reaction compared to phenylglycinol 15 (Scheme 7).
This result clearly indicates that the β-amino group has a dramatic
effect on the arylation process. The arylation of benzyl alcohol 28a
and 3-phenyl-1-propanol 28c provided the corresponding O-phenyl
ethers 29a and 29c in similar yields as 28b.
Cu(OAc)2 (1.0 equiv)
CH2Cl2, 50˚C, O2, o.n.
F
F
F
F
F
OH
F
F
O
F
F
31
F
30 (1.0 equiv)
Scheme
9
Competition
studies
between
2-
(pentafluorophenyl)ethanol 30 and N-BOC-phenylglycinol 15.
To further support our hypothesis, we performed the O-arylation of
aminoalcohol 32a-c where the distance between the amino group
and the alcohol is systematically increased by one methylene unit
(Scheme 10). The results indicate that the yield is higher for N-
BOC-ethanolamine 32a which has the lowest pKa. The yield then
decreases as the pKa increases, as shown by products 33b and 33c.
Ph3Bi (1.0 equiv)
Pyridine (3.0 equiv)
(
)
( )
OH
O
n
n
Cu(OAc)2 (1.0 equiv)
CH2Cl2, 50˚C, O2, o.n.
28a (n = 1)
28b (n = 2)
28c (n = 3)
29a (n = 1)
29b (n = 2)
29c (n = 3)
O
O
O
Ph3Bi (1.0 equiv)
OH
O
(
)
n
( )
BOCHN
BOCHN
n
29a (n = 1)
34%
29b (n = 2)
43%
29c (n = 3)
43%
"conditions"
32a (n = 1; pKa = 14.9)
32b (n = 2; pKa = 16.2)
32c (n = 3; pKa = 16.3)
33a (n = 1)
33b (n = 2)
33c (n = 3)
Scheme 7 O-Arylation of benzyl alcohol 28a, phenethyl alcohol
28b, and 3-phenyl-1-propanol 28c.
O
BOCHN
O
O
BOCHN
BOCHN
To evaluate the difference in reactivity between simple alcohols and
33a
52% (A)
49% (B)
33b
40% (A)
34% (B)
33c
40% (A)
42% (B)
1,2-aminoalcohols more accurately, we next performed
a
competition experiment between N-BOC-phenylglycinol 15 and
phenethylalcohol 28b (Scheme 8). After 16 hours, the 1H-NMR
analysis of the crude mixture indicated a ratio of O-phenyl-N-BOC
phenylglycinol 16 over 29b of 1.7:1.0, suggesting that an
aminoalcohol is more reactive than a simple alcohol.
Scheme 10 O-Arylation of N-BOC-ethanolamine 32a, 3-(N-BOC-
amino)-1-propanol 32b, and 4-(N-BOC-amino)-1-butanol 32c.
Conditions A: Ar3Bi (1.0 equiv), pyridine (1.2 equiv), Cu(OAc)2
(0.3 equiv), toluene, 80˚C, O2, o.n.; Conditions B: Ar3Bi (1.0
equiv), pyridine (3.0 equiv), Cu(OAc)2 (1.0 equiv), CH2Cl2, 50˚C,
O2, o.n.
a
NHBOC
OH
NHBOC
O
The results from Schemes 7 to 10 support our hypothesis that an
amino group in β-position relative to an alcohol accelerates the O-
arylation reaction mainly via an inductive effect.
Ph3Bi (1.0 equiv)
Pyridine (3.0 equiv)
16
15 (1.0 equiv)
ratio 16 : 29b = 1.7 : 1
Cu(OAc)2 (1.0 equiv)
CH2Cl2, 50˚C, O2, o.n.
OH
O
29b
28b (1.0 equiv)
Conclusions
Scheme 8 Competition studies between phenethylalcohol 28b and
N-BOC-phenylglycinol 15.
In summary, we have developed a copper-catalyzed O-arylation
reaction
of
1,2-aminoalcohols
using
functionalized
triarylbismuthanes. The reaction is promoted by catalytic
amounts of copper acetate and tolerates a variety of substituents
on the organobismuthane, giving access to functionalized β-
aryloxyamines. Different protecting groups can be used on the
aminoalcohol, such as BOC, Cbz, Ac, and Ts. Finally, we
demonstrated that the presence of an amino group in β relative
to the alcohol provides an increase in reactivity, probably
through inductive effect. The application of this protocol to the
arylation of other hydroxy-containing substrates is in progress
in our group and results will be reported in due course.
We then postulated that the difference in reactivity between 1,2-
aminoalcohols and simple alcohols could derive from an inductive
effect generated by the β-amino group, effectively lowering the pKa
of the alcohol moiety. To test this hypothesis, we performed a
second competition experiment between N-BOC-phenylglycinol 15
and pentafluorophenethylalcohol 30 (Scheme 9). After 16 hours, the
1H-NMR analysis of the crude mixture showed a ratio of the O-
phenyl-N-BOC
phenylglycinol
16
over
O-
phenylpentafluorophenethylether 30 of 1.1:1.0, thus demonstrating
that the pentafluoroalcohol 31 has a similar reactivity than N-BOC-
phenylglycinol 15 and therefore suggesting that the presence of
electron-withdrawing groups increases the reactivity of an alcohol.
To furnish further evidence of this effect, the aqueous pKa values for
alcohols 15, 28b, and 30 using a recent method reported by Pulay et
al.22 The calculations were carried out using ORCA 3.0.1.23 These
values were calculated to be 15.8 for 15, 17.3 for 28b, and 15.6 for
Acknowledgements
This work was supported by the Natural Sciences and
Engineering Research Council of Canada (NSERC), the
Université du Québec à Montréal (UQÀM) and the Centre in
Green Chemistry and Catalysis (CGCC). P.P. thanks the faculty
4 | J. Name., 2012, 00, 1-3
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of sciences of UQÀM for a FARE scholarship. J.D. thanks the
faculty of sciences of UQÀM for an undergraduate scholarship.
S.S. thanks NSERC for a USRA scholarship. F.P. thanks the
CGCC for an undergraduate scholarship. We thank Dr.
Alexandre Arnold for advanced NMR analyses. Computational
resources were provided by Calcul Québec and Compute
Canada.
8
For selected examples of SNAr reactions between 1,2-
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Notes and references
a
Département de chimie, Université du Québec à Montréal, C.P. 8888,
Succ. Centre-Ville, Montréal, Québec, Canada, H3C 3P8 and Centre in
Green Chemistry and Catalysis
b
Université Sherbrooke, Département de chimie, 2500 boul. de
l’Université, Sherbrooke, Québec, Canada, J1K 2R1 and Centre in Green
Chemistry and Catalysis
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
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For compound 9, see: V. Sandanayaka, B. Mamat, R. K.
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