Transition-Metal-Free Catalytic Carboalkoxylation of Styrenes at Room Temperature

Article abstract of DOI:10.1021/acs.joc.9b01744

Herein, we describe the first transition-metal-free catalytic carboalkoxylation of styrenes with aryl diazonium salts by Meerwein addition in the presence of a phenalenyl ligand at room temperature without requiring any light stimulation. This three-compo

Full text of DOI:10.1021/acs.joc.9b01744

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Article
Transition Metal-Free Catalytic Carboalkoxylation
of Styrenes at Room Temperature
R Govindarajan, Jasimuddin Ahmed, Asim Kumar Swain, and Swadhin K. Mandal
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b01744 • Publication Date (Web): 18 Sep 2019
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Transition Metal-Free Catalytic Carboalkoxylation of
Styrenes at Room Temperature
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R. Govindarajan,≠ Jasimuddin Ahmed,≠ Asim Kumar Swain and Swadhin K. Mandal*
Department of Chemical Sciences, Indian Institute of Science Education and Research-Kolkata,
Mohanpur-741246, India.
ABSTRACT: Herein, we describe the first transition metal-free catalytic carboalkoxylation of
styrenes with aryl diazonium salts by Meerwein addition in the presence of a phenalenyl ligand
(PLY) at room temperature without requiring any light stimulation. This three-component reaction
allows facile di-functionalization of styrene derivatives with various alcohols (such as 1, 2 and
3) as the source of alkoxy group during this transformation. The key intermediates and the
transition states involved in this reaction path were unraveled by a series of control experiments
coupled with density functional theory (DFT) calculations. The full mechanistic investigations
provide an understanding of the selectivity towards carboalkoxylation (Meerwein arylation
addition-elimination) in presence of various alcohols over the simple arylation to multiple bond
(Meerwein arylation-elimination) reaction.
KEYWORDS: Carboalkoxylation, Transition metal free catalysis, Phenalenyl ligand, Styrene di-
functionalization, Meerwein arylation-elimination.
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INTRODUCTION:
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Over the last decades, a numerous strategies was developed for functionalization of alkenes such
as olefin polymerization,1 hydrosilylation,2 hydroamination,3 carboxylation,4 reductive alkylation,
simple arylation5 etc. Such protocols for functionalization of alkenes are highly important in an
extensive range of applications covering medicines, materials and polymer chemistry.6 In this
context, a relatively new methodology has been devised for di-functionalization of alkenes, which
involves the formation of two different chemical bonds across the C-C double bond by utilizing
three different chemical components.7-9 In 2010, Toste and co-workers developed a gold catalyzed
intermolecular oxyarylation of alkenes by using boronic acid coupling partner in presence of
selectfluor oxidant at 50 C.10 Later on, Glorius and co-workers introduced an Au-Ru based dual
catalyst to perform intramolecular oxyarylation reaction of alkene by using aryl diazonium salt
coupling partners in presence of light.11 Subsequently, research groups of Itoh12, Greaney13, and
König,14 have developed the intermolecular oxyarylation of alkene under light stimulation using
Ru or Ir based catalyst and diphenyliodinium or aryl diazonium salt as the arylating component
(Scheme 1a). All these methods have been carried out by the photoinduced electron transfer from
the catalyst to the aryl diazo/iodonium salt coupling partner to generate aryl radical. This aryl
radical subsequently attacks the terminal carbon of the alkene to generate a benzylic radical.
Subsequently, the benzyl radical regenerates the catalyst by a single electron transfer (SET2)
resulting in the formation of a benzylic cation (Scheme 1a). A parallel effort to avoid the transition
metal based catalysts was introduced by using an equivalent amount of TEMPONa where
TEMPONa and aryl diazonium salt reacted to generate aryl radical which reacted with styrene to
provide the corresponding oxyarylated products (Scheme 1b).15 Further efforts by Heinrich and
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co-workers avoiding transition metal based catalysts, described the use of stoichiometric amount
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of KOAc under heating to accomplish carbohydroxylation of α-methylstyrene.16
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a) Ir/Ru catalysis using light as external stimuli b) Transition metal-free stoichiometric reaction
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
Ar1
Nu/E
Ar
Ar1
Ar 
Ar-N2BF4
Ar1
Ar
E
E
Ir(IV)/Ru(III)
Ar-X

SET 2
Ar1
SET 1
SET 1
Nu-H/E
Ar
Nu-H
Ar1
X = IAr, N2BF4
Ir(III)/Ru(II)

Ir(III)*/Ru(II)*
Ar1
Ar 
Ar
Nu
Ar1
h

Ar
c) Our approach:
The first transition metal-free catalytic protocol without any external stimuli.

Nu
H-Nu
Ar
Ar1
Ar1

Ar-N2BF4
Ar1
Ar
Ar
[PLY K]
[PLY K]
[PLY K]
[PLY K]
Less
Favoured
SET 1
SET 2
SET 2'
Favoured

X
Y
H-Nu

X, Y = N, O etc
Ar 
Ar1
Ar1
Phenalenyl ligand
(PLY)
Ar
Ar1
Nu-H
Ar
Scheme 1. (a) Previous work on di-functionalization of styrenes using transition metal based
catalysts under light/heat activation. (b) Previous work on transition metal-free stoichiometric
reactions on di-functionalization of styrenes. (c) This work describing the first transition metal-
free catalysis for carboalkoxylation of styrenes at room temperature without requiring any light
stimulation.
In both of these studies, only aryl radical generation was taken care of by a single electron donation
from an equivalent amount of electron donor such as TEMPONa/KOAc (Scheme 1b), however
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none of these approaches was catalytic. As a result, till date, no report is available which can avoid
transition metals to perform this fascinating transformation in a catalytic fashion. The current study
documents the first transition metal-free catalytic carboalkoxylation of styrenes under ambient
conditions using phenalenyl based radical (Scheme 1c). In recent years, we adopted a strategy to
avoid transition metal catalysts utilizing an odd alternant hydrocarbon, phenalenyl which takes
advantage of a readily accessible non-bonding molecular orbital (NBMO).17 Earlier, relatively
stable phenalenyl radicals with singly occupied molecular orbital (SOMO), generated by the
reduction of phenalenyl cation have been utilized in designing various smart materials by research
groups of Haddon18, 19, Takui20, Kubo21, Morita22 and co-workers. The major advantage of
phenalenyl based radical as a catalyst has been argued and demonstrated in a few synthetically
important chemical transformations and the topic of using phenalenyl radical in catalysis was
recently reviewed.23 In particular, recent applications of phenalenyl radicals for various catalytic
protocols such as C-C coupling24-25, electrocatalysis in H2O2 fuel cell26, hydrosilylation27 as well
as in spin filtration28 are worth to mention. In the present study, we used an in-situ generated
phenalenyl-K complex based radical as the redox catalyst for carboalkoxylation of different
styrenes with both activated and unactivated diazonium salt coupling partners in presence of
different alcohols (1o, 2o and 3o) at room temperature without requiring any light stimulation
(Scheme 1c). This catalytic transition metal-free approach successfully accomplishes both
carboalkoxylation in the presence of alcohol and simple arylation (Meerwein arylation-
elimination) in absence of alcohol for the first time. Computational studies with experimental
evidences in tandem delineated the underlying mechanistic pathway, which in particular helped us
in understanding the origin of selectivity observed towards carboalkoxylation vs simple arylation
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reaction as a function of alcohol used. DFT calculations were performed to understand the
feasibility of single electron transfer (SET) processes involved in the catalytic cycle.
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RESULTS AND DISCUSSION:
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We started our investigation by optimizing the reaction conditions for methoxyarylation of 4-
methoxystyrene (1a, 1equiv.) with electronically unbiased phenyl diazoniumtetrafluoroborate (2a,
1 equiv.) coupling partner in the presence of PLY-N,O ligand (I) and KOtBu (20 mol%) as a base
in DMSO under room temperature for 24 h to afford 38% yield of corresponding methoxyarylated
product 3aa (Table 1, entry 1). By varying the loading of diazonium salt coupling partner (2a)
from 2 equiv. and 3 equiv., the yield of 3aa increased to 50% and 64%, respectively (Table 1,
entries 4-5). In absence of PLY-N,O, keeping all other conditions unchanged, only 8% of 3aa
formation was noted (Table 1, entry 2). In absence of potassium tertiary butoxide, only less than
5% product formation was observed (Table 1, entry 3). The screening of other solvents and bases
did not give any better result (Table 1, entries 6−8). In order to investigate the role of PLY-N,O
ligand on the catalytic activity, an identical study was performed using a PLY-O,O (II), PLY-N,N
(III) and PLY-N,O cation (IV). It resulted in only 35, 40 and 23% of the methoxyarylated product,
respectively (Table 1, entries 9-11). Low ligand and base loading shows lowering down in the
yield to 57% and 38% of product 3aa with the ligand loading 7.5 mol% and 5 mol%, respectively
(Table 1, entry 12 and 13). Further, two sets of reaction were performed by varying the amount of
methanol (200 L and 600 L) which offered 35% and 50% yield of the product 3aa, respectively
(Table 1, entries 14 and 15). When the same reaction was conducted following protocol described
in entry 16 and was carried out for 18 h, it resulted in almost similar yield of the methoxyarylated
product (3aa, 55%).
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Table 1. Reaction optimization for methoxyarylation of 4-methoxystyrene with phenyldiazonium
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tetrafluoroborate salt at room temperature.
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OMe
Ligand (X mol%)
F4BN2
+
MeO
Additive (Y mol%),
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Solvent, MeOH,
25 °C, 24 h
MeO
1a
2a
3aa
BF4

O
HN
O
OH
N
HN
O
HN

PLY-N,O
(I)
PLY-O,O
(II)
PLY-N,N
(III)
PLY-N,O Cation
(IV)
Entry
2a
(equiv.)
Ligand
(mol%)
Base (mol%)
Solvent
Yield %
1.
2.
3.
4.
5.
6.
7.
8.
1
1
1
2
3
3
3
3
3
3
3
3
3
I (10)
-
KOtBu(20)
KOtBu(20)
-
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
38
8
5
I (10)
I (10)
I (10)
I (10)
I (10)
I (10)
II (10)
III (10)
IV (10)
I (7.5)
I (5)
KOtBu(20)
KOtBu(20)
KOtBu(20)
KOtBu(20)
NaOtBu(20)
KOtBu(20)
KOtBu(20)
K (20)
KOtBu(15)
KOtBu (10)
KOtBu (20)
KOtBu (20)
KOtBu(20)
50
64
53
NR
52
35
40
23
57
38
THF
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
9.
10.
11.
12.
13.
14.
15.
16.
3
3
3
I (10)
I (10)
I (10)
DMSO
DMSO
DMSO
35b
50c
55d
aReaction conditions: 1a (0.24mmol), 2a (0.72 mmol) and MeOH (0.8 mL), 24 h. The reaction
was carried out by using 200 L MeOH. cThe reaction was carried out by using 600 L MeOH.
dThe reaction was continued for 18 h.
b
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From all these different reaction combinations, it can be concluded that the reaction between 4-
methoxystyrene (1a) and phenyldiazonium tetrafluoroborate salt (2a) in presence of 10 mol % of
PLY-N,O and 20 mol % of KOtBu in DMSO for 24 h is the best condition to obtain the maximum
yield (64%) of methoxyarylated product 3aa (Table 1, entry 5).
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With this optimized reaction condition, we started investigating the versatility and the reaction
scopes of this protocol. Different diazonium salt coupling partners were tested for
methoxyarylation of 4-methoxystyrene (1a). All the diazonium salts bearing electron withdrawing
group (EWG) such as 2-F (2b), 4-Cl (2e), 4-Br (2f), 3,5-dichloro (2g), 4-NO2 (2h) afforded good
to excellent isolated yields (65-84%) of the corresponding methoxyarylated products (3ab-3ah) of
4-methoxystyrene (1a, Scheme 2). Notably, only diazonium salt coupling partners bearing electron
donating group (EDG) such as 4-Me (2i), 4-OMe (2j) afforded moderate to good yields (52-55%)
of the corresponding products (3ai-3aj). Using 4-methylstyrene (1b), the present protocol
delivered good yields (59-75%) of the corresponding carboalkoxylated products (3ba-3bh) for
various aryl diazonium salt coupling partners. When simple styrene (1c) was taken for the
carboalkoxylation with 4-nitrophenyldiazonium (2h) coupling partner, the isolated yield was
reduced to 38% (3ch). We performed four different reactions for preparation of carboalkoxylated
products, 3aa, 3ba and 3aj in absence of catalyst which afforded 17%, 13%, and 10% product
formation, respectively (see ESI, Scheme S2). This indicates that the presence of catalyst is
required to obtain satisfactory yield of the carboalkoxylated products.
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R2
4
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OMe
PLY-N,O (10 mol%)
F4BN2
+
R2
KOtBu (20 mol%)
R1
1a
R1
DMSO, MeOH, 25 °C, 24 h
1b
R1 = 4-OMe ( ), 4-Me ( ),
2a
2c
2b
R2 = H ( ), 2-F ( ),
3
1c
1d
H ( ), 4-Me ( ),
2d
3-Cl ( ), 3-Br ( ),
1e)
1f
2, 5-Me ( ,4-tert ( ),
2e 2f
4-Cl ( ), 4-Br ( ),
2g 2h
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1g
1h
4-Ph ( ), 4-OEt ( ),
3, 5-Cl ( ), NO2 ( ),
1i
)
2-vinylnaphthalene (
2i
2j
)
4-Me ( ), 4-OMe (
Cl
Cl
Br
OMe
OMe
OMe
OMe
OMe
3ag
Cl
F
O
O
O
O
3af
83%
3ab
83% (90%)
3ae
65% (88%)
O
3aa
64%
72%(85%)
OMe
NO2
OMe
OMe
OMe
OMe
OMe
F
O
O
O
3bb
3ba
59%
3ah
84% (>99%)
3ai
52% (63%)
3aj
55%
69% (86%)
Cl
Cl
Br
NO2
OMe
OMe
OMe
OMe
OMe
Br
Cl
3be
65% (85%)
3bf
68% (90%)
3bg
68%
3bd
75%
3bh
63%(93%)
NO2
NO2
NO2
NO2
OMe
OMe
OMe
OMe
OMe
Cl
3ch
38%(47%)
3eh
51%
3fc
76%
3dh
3fh
68%
51%(58%)
NO2
O
NO2
NO2
OMe
Cl
OMe
OMe
OMe
OMe
Br
3fd
70%
3gh
54%(58%)
3fe
62%
3hh
61%
3ih
48%
Scheme 2. Transition metal-free methoxyarylation of different styrenes with various diazo
coupling partners at room temperature. Reaction conditions: 1a-i (0.24 mmol), 2a-j (0.72 mmol),
catalyst (0.024 mmol), KOtBu (0.048 mmol), DMSO (0.8 mL), MeOH (0.8 mL). In the
parentheses, conversion by 1H NMR spectroscopy is noted.
Next, the reaction scope was further checked over different styrenes bearing 2-Me (1d), 2,
5-Me (1e), 4-tertiary butyl (1f), 4-Ph (1g) and 4-OEt (1h) groups, which afforded moderate to good
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yields (51-76%) of the corresponding methoxyarylated products (3dh-3hh). The electron
withdrawing group (such as -NO2, -CN and -F) containing styrenes as well as aliphatic alkene
remained unsuccessful for carboalkoxylation reaction under this current protocol (see ESI, Scheme
S2).
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Polyaromatic styrene such as 2-vinylnaphthalene (1I) was also considered for the same reaction
with 4-nitrophenyldiazonium salt (2h), which delivered 48% isolated yield of the corresponding
product 3Ih (Scheme 2). These results thus demonstrate the applicability of the current protocol
for various styrenes. Encouraged by the versatility towards different styrenes and diazonium
coupling partners, further we checked the effect of different alcohols (such as 1, 2 and 3).
Previous reports were limited over the use of mainly primary and secondary alcohols.10, 12 In this
current protocol, different alcohols such as 1, 2 and 3 were used as the source of alkoxy partner
(Scheme 3a). The primary alcohols led to satisfactory yields (52-84%) of the products (Schemes
2 and 3a including 4ah using ethanol) using 4-methoxystyrene as a coupling partner. When
isopropanol was used, moderate yield of the carboalkoxylated compound (5ah) was obtained
(53%, Scheme 3a) as the major product along with simple arylated product in 7:3 ratio. This ratio
of carboalkoxylated product to simple arylated product increased to 1:1 when a tertiary alcohol
such as tert-butanol was used as the source of alkoxy partner (see later for further details). Apart
from the simple arylated product, the tert-butoxyarylated product (6ah) was obtained in 23%
isolated yield, respectively (Scheme 3a). Such significant yield of simple arylated product during
the alkoxylation with tert-butanol insisted us to check the reaction in absence of any alcohol.
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NO2
OR1
PLY-N,O (10 mol%)
NO2
F4BN2
+
KOtBu (20 mol%)
R
DMSO, R1OH, 25 °C, 24 h
R
2h
1a
1b
R = 4-OMe ( ), 4-Me ( ),
4
5
R1 = Et ( ), IPr ( ),
6
tert-Bu ( )
9
a) In presence of different alcohol.
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NO2
NO2
NO2
NO2
O
O
O
O
O
O
4ah
78%
4bh
55%
O
6ah
23%
5ah
53%
b) In absence of alcohol (simple arylation).
NO2
NO2
NO2
NO2
NO2
O
11ah
68%
9ah
45%
7ah
75%
8ah
73%
10ah
63%
NO2
NO2
NO2
NO2
O
12ah
65%
13ah
65%
14ah
42%
15ah
48%
NO2
NO2
c)
NO2
OR
PLY-N, O (10 mol%)
KOtBu (20 mol%),
+
MeO
+
F4BN2
DMSO, ROH (X L) ,

MeO
MeO
1a
2h
7ah
3ah (R = Me)
6ah (R = tBu)
25 °C, 24 h
(1 equiv.)
(3 equiv.)
Entry
ROH
Total product 3ah or 6ah
formation
>99%
>99%
>99%
>99%
7ah
(X L; Y mmol)
MeOH (200; 4.9)
MeOH (400; 9.8)
tBuOH (465; 4.9)
tBuOH (936; 9.8)
1.
2.
3.
4.
74 (3ah)
66 (3ah)
39 (6ah)
48 (6ah)
26
34
61
52
Scheme 3. a) Carboalkoxylation with 1, 2 and 3 alcohols. Reaction conditions: 1a-b (0.24
mmol), 2h (0.72 mmol), catalyst (0.024 mmol), KOtBu (0.048 mmol), DMSO (0.8 mL), alcohol
(0.8 mL); b) Reaction carried out in absence of alcohol. c) Reactions under different concentration
of alcohols (MeOH and tBuOH).
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In absence of any alcohol, only simple arylated product 7ah was found by reaction of 4-
methoxystyrene (1a) with 4-nitrophenyl diazonium salt coupling partner (2h) resulting in 75%
isolated yield. Following this observation, different styrenes were considered for this reaction in
absence of alcohol to understand if this is a general trend, and we obtained the simple arylated
products 7ah-15ah in moderate to good yields (42%-75%, Scheme 3b). This result establishes
efficacy of this catalytic protocol as a common platform for both carboalkoxylation as well as
simple arylation reaction. Keeping the above results in mind, it may be concluded that the present
transition metal-free catalytic method is versatile towards different sets of styrenes, diazo coupling
partners as well as alcohols. To understand the influence of alcohol concentration on the ratio of
carboalkoxylation and Meerwein arylation-elimination products, four different sets of reaction
were carried out separately maintaining an identical concentration of methanol and tert-butanol
(Scheme 3c). It may be noticed that the amount of carboalkoxylated product is higher for methanol
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t
than that of the tert-butanol; for example, 9.8 mmol of BuOH resulted in 48:52 ratio of
carboalkoxylation and Meerwein arylation-elimination product whereas similar concentration of
MeOH resulted in 74:26 ratio for the same (Scheme 3c; see ESI, Figures S1-S4 for details). These
results (presented in Scheme 3c) clearly indicate that the ratio of carboalkoxylation and Meerwein
arylation-elimination product is not only dependent on the amount of alcohol but also on the nature
of alcohol.
Given an illustrious scope of the reaction, we started to investigate the mechanistic pathway of this
reaction. At first, the catalytic reaction was performed in presence of a radical scavenger. The
catalytic reaction of 4-methoxystyrene (1a) and 4-nitrophenyldiazonium salt coupling partner (2h)
in presence of 10 mol% of a radical scavenger TEMPO, could slow down the reaction almost
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completely (24%, Scheme 4a), while 1 equiv. TEMPO almost completely shuts down the reaction
(<5%, Scheme 4a). This observation indicates that this reaction is mediated through radical.
7
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9
a)
NO2
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PLY-N,O (10 mol%)
NO2
F4BN2
+
KOtBu (20 mol%)
DMSO, 25 °C, 24 h
TEMPO (10 mol%)
MeO
MeO
1a
2h
7ah
TEMPO (10 mol%) 24%
TEMPO (1 equiv.) < 5%
b)
NO2
PLY-N,O (10 mol%)
N
O
O
N
NO2
F4BN2
+
KOtBu (20 mol%)
DMSO, 25 °C, 24 h
TEMPO (1 equiv.)
+
MeO
O2N
1a
2h
MeO
17
16
Scheme 4. a) Reaction inhibition in presence of a radical quencher TEMPO. b) Trapping of radical
intermediate. Reaction condition: 1a (0.24 mmol), 2a (0.72 mmol), catalyst (0.024 mmol), KOtBu
(0.048 mmol), DMSO (0.8 mL), CH3OH (0.8 mL).
To further confirm this, the stoichiometric version of this reaction using an equivalent amount of
TEMPO was investigated by mass spectroscopic measurement, which reveals the molecular peaks
at (M+H = 256.6379 (16) and 413.8648 (17), clearly authenticating the formation of compounds
16 and 17 (Scheme 4b). Furthermore, compound 16 was isolated and characterized with the help
of 1H and 13C NMR spectroscopic techniques and matched the spectroscopic data with the previous
report.29 These controlled experiments and the characterization of the trapped intermediates clearly
support a radical mediated mechanistic pathway. Moreover, to understand the rate determining
step (r.d.s) of this reaction, a kinetic isotope effect (KIE) experiment was also conducted for the
same methoxyarylation reaction. A series of parallel reactions was carried out using CH3OH and
CD3OD separately under our catalytic condition for the carboalkoxylation of 4-methoxystyrene
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(1a) with phenyldiazonium salt (see SI, Scheme S1). The reactions were stopped after different
time interval in each case and the product formation was quantified by 1H NMR spectroscopy in
presence of an internal standard (4-nitrotoluene). Comparing their rates, the KH/KD value was
measured as 1.26. This value indicates that O-H bond breaking is not directly involved during the
rate determining step (r.d.s) of this reaction.
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
F
-e
NO2
Ar1
Ar2
=
=
[(PLY-N,O)-K]1-
[(PLY-N,O)-K]
F
B
F
r3
F
B
+e
F
r1: 1.20 Å
r2: 1.53 Å
r3: 1.48 Å
F
OMe
F
r2
F
H
r1
H
Int3a
HOMO
Ar1
Ar2
Ar1
0.0
1
Ar2
TSh
-26.6
-40.8
IntH
-39.0
-44.6
Path II
+
-
Ar1-N2
BF4
Simple Meerwein Arylation
Ar1
NO2
Ar2
e
Int2
-57.0
-56.4
Int1
HOMO
N2
GSMD
3a'
TSf
-42.3
-46.5
MeO
3a'
-
GCPCM
Int3b
-51.9
-51.9
BF4
e
Ar1
DMSO
e
IntF
-54.7
-60.0
Msty
(Kcal/mol)
Int1
2
Int3a

F
B
r4
-102.6
-100.2
-68.8
-77.1
-61.9
-69.6
F
r3
F
Path I
Carboalkoxylation
3a
MeOH
H
r2
F
F
F
H
Me
F
B
O
r1
+
Me
M
H
Me
O
F
H
H3C
NO2
e
O
O
O
Ar1
Ar2
Ar1
Ar1
Ar1
r1: 2.24 Å
r2: 0.98 Å
r3: 1.76 Å
r4: 1.43 Å
Ar2
Ar1
HOMO
Ar1
Ar2
Ar2
Ar2
TsF
3a
MeO
Int1
Int3b
Int3a
IntF
Scheme 5. Calculated energy profile diagram for the methoxyarylation reaction and simple
arylation reaction of 4-methoxystyrene with 4-nitrophenyl diazo coupling partner.
Based on the experimental results and detailed DFT calculations (using Gaussian 0930 at
M062X/UM062X level of theory by using 6-311+g(d,p)31 considering both CPCM32 and SMD
solvent model), a proposed mechanism is outlined in Scheme 5. In our earlier studies, it was
demonstrated that PLY-N,O reacts with KOtBu (1:1) to form a (PLY-N,O)-K complex, which can
be reduced by another equivalent of KOtBu to obtain a monoreduced (PLY-N,O)-K radical anionic
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complex.24 In this work, theoretical calculations reveal an electron transfer from the SOMO of the
5
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+
monoreduced (PLY-N,O)-K radical complex to the anti-bonding orbital of Ar-N2 at ambient
7
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9
condition to generate an aryl radical (Ar•), and the free energy change for formation of such aryl
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radical is thermodynamically feasible (G = -68.3 Kcal/mol). Further, this radical was also
1
13
experimentally trapped by a radical quencher TEMPO and characterized by H, C NMR and
mass spectroscopy (16, Scheme 4b). Calculated HOMO of this aryl radical reveals the maximum
localization of electron spin density is at the para-carbon atom with respect to NO2 group. This in-
situ generated aryl radical next can attack the terminal carbon atom of the 4-methoxystyrene
resulting in the formation of a radical intermediate (Int1), which was also trapped as 17 by the
radical scavenger TEMPO and characterized by mass spectroscopy (Scheme 4b). The Int1 next
can release an electron to regenerate the monoreduced (PLY-N,O)-K radical complex and cationic
intermediate (Int2). However the calculation suggests such process is slightly more energy
demanding (45.6 Kcal/mol) with respect to another reaction pathway involving intermediate Int3a
(40.7 Kcal/mol), which can be accessed only in presence of an alcohol such as methanol. The
access of such less energetic intermediate Int3a in presence of methanol explains our results in
obtaining selectively carboalkoxylated product (3a) over the simple arylation product (3a'). This
Int3a in such case (in presence of methanol for example), can release one electron to generate the
cationic carboalkoxylated intermediate (Int3b) regenerating the monoreduced (PLY-N,O)-K
radical complex. However, it may be noted that the current experimental results are not sufficient
to distinguish between these two possible mechanisms and the present mechanistic proposal is

drawn on the basis of computational data. The Int3b further can interact with BF4 through a
transition state TSf leading to bond cleavage between O-H and B-F while forming a F-H bond
(Scheme 6) with calculated thermodynamic parameter of (G≠ = 9.9 Kcal/mol (SMD)/5.4
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Kcal/mol (CPCM), Scheme 5). This step is exothermic in nature by -19 Kcal/mol (Scheme 5). On
the other hand, in absence of any alcohol, the same reaction leads to the selective formation of
simple arylated product (3a'), which can be explained by direct removal of an electron from Int1
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
to form a cationic intermediate Int2. In presence of BF4 ion, a proton abstraction from the Int2
results in the formation of product 3a' through the transition state [TSh, 30.1 (SMD)/15.6 (CPCM)
Kcal/mol]. This transition state involves the C-H and B-F bond dissociation as well as H-F bond
formation (Scheme 5).
Scheme 6. Comparison of the energy levels of corresponding intermediates for different alcohols
and simple arylation to understand selectivity of this transformation.
Interestingly, when higher analogue of the alcohol was used instead of methanol, a competition
between simple arylation product and carboalkoxylated product was observed. For example, in
case of isopropanol, carboalkoxylated and simple arylation products were observed in the ratio of
7:3, whereas tert-butanol leads to 1:1 ratio of such products formation. This observation clearly
indicates that the choice of alcohol plays a major role in determining selectivity of the process. To
understand such selectivity, we resorted to the DFT by calculating the energy of Int3a, Int3a' and
Int3a'' which are adducts of the radical intermediate (Int1) with different alcohols such as
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methanol, isopropanol (iPrOH) and tert-butanol (tBuOH), respectively. In case of methanol, energy
difference between Int2 and Int3a is 4.6 Kcal/mol. This energy gap gradually decreases to 3.1
Kcal/mol (between Int3a' and Int2) and 1.8 Kcal/mol (between Int3a'' and Int2) for iPrOH and
tBuOH, respectively (Scheme 6). As this energy gap decreases, the selectivity towards the
carboalkoxylated product also diminishes.
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CONCLUSIONS:
In conclusion, we have developed the first transition metal-free catalytic protocol for the
carboalkoxylation of styrenes. Various styrenes containing electron donating group and diazonium
coupling partners containing both electron donating as well as electron withdrawing groups were
successfully screened for this reaction to afford structurally diverse carboalkoxylated products.
The present protocol is effective for simple arylation in absence of alcohol as well as it successfully
delivers carboalkoxylated products in presence of methanol under ambient conditions, thus
representing an operationally convenient and economically attractive alternative to the reported
rare metal and light mediated methodologies. The mechanistic pathway of this reaction was
proposed by carrying out a detailed density functional theory (DFT)-based investigation of the
catalytic cycle in combination with several experimental evidences.
EXPERIMENTAL SECTION:
General considerations.
Solvents were dried using standard methods and freshly distilled prior to use.33 All chemicals were
purchased and used as received. The 1H and 13C {1H} NMR spectra were recorded on 400 MHz
(JEOL) and 500 MHz (BRUKER) spectrometers in CDCl3 with residual undeuterated solvent
(CDCl3, 7.26/77.00) as an internal standard. Chemical shifts (δ) are given in ppm, and J values are
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given in Hz. All chemical shifts were reported in ppm using tetramethylsilane as a reference.
Chemical shifts (δ) downfield from the reference standard were assigned positive values. Open-
column chromatography and thin-layer chromatography (TLC) were performed on silica gel
(Merck silica gel 100-200 mesh) and aluminium oxide active neutral activity I-II (Merck). High-
resolution mass spectra (HRMS) were obtained on a BrukermaXis impact and Agilent 6530 Q-
TOF mass spectrometer using electron spray ionization mass spectroscopic technique. ESI-mass
spectra were taken on a Water Q-TOF micro mass spectrometer. Melting points were measured
on a Büchi melting point B-545 apparatus.
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All aryldiazonium tetrafluoroborate salts were prepared following the previous literature reports.
34-37
Reaction procedure for optimization study on methoxyarylation of styrenes (3aa-3ih).
Substituted styrene (0.24 mmol, 1 equiv.), diazocoupling partner (0.72 mmol, 3 equiv.), PLY-N,O
(0.024 mmol, 0.1 equiv.), KOtBu (0.048 mmol, 0.2 equiv.) were taken in a 25 mL quartz tube,
DMSO (0.8 mL ) and methanol (0.8 mL) were poured into the reaction mixture inside a nitrogen
filled glovebox. The final reaction mixture was allowed to stir for required time at 25 C. After
completion of the reaction, product was extracted using 30 mL ethyl acetate (EA) and dried over
anhydrous sodium sulphate. The solvent was removed under reduced pressure and crude product
was purified by column chromatography on silica gel (Merck silica gel 100-200 mesh) using
hexane/EtOAc mixture to yield the pure desired products.
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General procedure for carboalkoxylation of styrenes (4ah-6ah).
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Substituted styrene (0.24 mmol, 1 equiv.), diazocoupling partner (0.72 mmol, 3 equiv.), PLY-N,O
(0.024 mmol, 0.1 equiv.), KOtBu (0.048 mmol, 0.2 equiv.) were taken in a 25 mL pressure tube,
DMSO (0.8 mL) and alcohol (0.8 mL) were poured into the reaction mixture inside a nitrogen
filled glovebox. The final reaction mixture was allowed to stir for 24 h at 25 C. After completion
of the reaction, the product was extracted using 30 mL ethyl acetate (EA) and dried over anhydrous
sodium sulphate. The solvent was removed under reduced pressure and crude product was purified
by column chromatography on silica gel (Merck silica gel 100-200 mesh) using hexane/EtOAc
mixture to yield the pure desired products.
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Large scale preparation of 6ah.
4-Vinylanisole (1a, 2.4 mmol, 320 L, 1 equiv.), 4-nitrophenyldiazocoupling partner (2h, 7.2
mmol, 1.7 g, 3 equiv.), PLY-N,O (0.24 mmol, 50 mg, 0.1 equiv.), KOtBu (0.48 mmol, 60 mg, 0.2
equiv.) were taken in a 100 mL pressure tube, DMSO (5 mL) and tBuOH (5 mL) were poured into
the reaction mixture inside a nitrogen filled glovebox. The final reaction mixture was allowed to
stir for 24 h at 25 C. After completion of the reaction, the product was extracted using 30 mL
ethyl acetate (EA) and dried over anhydrous sodium sulphate. The solvent was removed under
reduced pressure and crude product was purified by column chromatography on silica gel (Merck
silica gel 100-200 mesh) using 1% EtOAc in n-hexane mixture to yield the pure desired products.
110 mg (14%) of compound 6ah was isolated as yellow colored solid.
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General Procedure for Meerwein arylation-elimination (7ah-15ah).
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Substituted styrene (0.24 mmol, 1 equiv.), diazocoupling partner (0.72 mmol, 3 equiv.), PLY-N,O
(0.024 mmol, 0.1 equiv.), KOtBu (0.048 mmol, 0.2 equiv.) were taken in a 25 mL pressure tube,
DMSO (0.8 mL) was poured into the reaction mixture inside a nitrogen filled glovebox. The final
reaction mixture was allowed to stir for 24 h at 25 C. After completion of the reaction, product
was extracted using 30 mL ethyl acetate (EA) and dried over anhydrous sodium sulphate. The
solvent was removed under reduced pressure and crude product was purified by column
chromatography on neutral aluminium oxide using hexane/EtOAc mixture to yield the pure desired
products.
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Physical Properties and Characterization Data of the Synthesized Compounds:
1-[2-Methoxy-2-(4-methoxyphenyl)ethyl]benzene (3aa)
Prepared according to general procedure described above by reacting 4-methoxystyrene (32 L,
0.24 mmol, 1 equiv.), phenyldiazonium tetrafluoroborate (138 mg, 0.72 mmol, 3 equiv.) with
methanol (0.8 mL, 83 equiv.). The title compound was purified by column chromatography with
silica gel using 1% EtOAc in n-hexane as a pale yellow solid (37 mg, 64 %). Data are in accordance
with previous literature reports.13 1H NMR (400 MHz, CDCl3, 298 K) δ (ppm) 7.27 – 7.15 (m,
5H), 7.15 – 7.09 (m, 2H), 6.87 (d, J = 8.0 Hz, 2H), 4.29 (m, 1H), 3.82 (s, 3H), 3.18 (s, 3H), 3.15
(dd, J = 16.0, 8.0 Hz, 1H), 2.90 (dd, J = 12.0, 4.0 Hz, 1H). 13C {1H} NMR (100 MHz, CDCl3, 298
K) δ (ppm) 159.0, 138.5, 133.6, 129.5, 128.0, 128.0, 126.0, 113.8, 84.6, 56.5, 55.2, 44.7.
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1-[2-Methoxy-2-(4-methoxyphenyl)ethyl]-2-fluorobenzene (3ab)
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9
Prepared according to general procedure described above by reacting 4-methoxystyrene (32 L,
0.24 mmol, 1 equiv.), 2-fluorophenyldiazonium tetrafluoroborate (155 mg, 0.72 mmol, 3 equiv.)
with methanol (0.8 mL, 83 equiv.). The title compound was purified by column chromatography
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1
with silica gel using 1% EtOAc in n-hexane as pale yellow oil (52 mg, 83 %). H NMR (400
MHz, CDCl3, 298 K) δ (ppm) 7.17 (m, 3H), 7.06 – 6.96 (m, 3H), 6.85 (d, J = 8.0 Hz, 2H), 4.33 (t,
1H), 3.80 (s, 3H), 3.22-3.11 (m, 4H), 2.91 (dd, J = 16.0, 8.0 Hz, 1H). 13C {1H} NMR (100 MHz,
CDCl3, 298 K) δ (ppm) 161.3 (d, J = 244.0 Hz), 159.1, 133.5, 131.9 (d, J = 4.0 Hz), 127.8, 125.5
(d, J = 15.0 Hz), 123.6 (d, J = 3.0 Hz), 115.1 (d, J = 22.0 Hz), 113.6, 83.1, 56.6, 55.2, 37.8. 19F
{1H} NMR (376 MHz, CDCl3, 298 K) δ (ppm) 118.2.HRMS m/z calcd for C15H14FO (M-
MeOH+H): 229.1029, found 229.1038.
1-[2-Methoxy-2-(4-methoxyphenyl)ethyl]-4-chlorobenzene (3ae)
Prepared according to general procedure described above by reacting 4-methoxystyrene (32 L,
0.24 mmol, 1 equiv.), 4-chlorophenyldiazonium tetrafluoroborate (163 mg, 0.72 mmol, 3 equiv.)
with methanol (0.8 mL, 83 equiv.). The title compound was purified by column chromatography
1
with silica gel using 1% EtOAc in n-hexane as a brown oil (43 mg, 65%). H NMR (400 MHz,
CDCl3, 298 K) δ (ppm) 7.19 (d, J = 8.0 Hz, 2H), 7.12 (d, J = 8.0 Hz, 2H), 7.00 (d, J = 8.0 Hz,
2H), 6.86 (d, J = 8.0 Hz, 2H), 4.23 (m, 1H), 3.81 (s, 3H), 3.16 (s, 3H), 3.09-3.04 (dd, J = 12.0, 4.0
Hz, 1H), 2.84 (dd, J = 12.0, 4.0 Hz, 1H). 13C {1H} NMR (100 MHz, CDCl3, 298 K) δ (ppm)
159.1, 136.9, 133.2, 131.8, 130.8, 128.1, 127.9, 113.7, 84.3, 56.4, 55.1, 43.9. HRMS m/z calcd
for C15H14ClO (M-MeOH+H): 245.0733, found 245.0726.
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1-[2-Methoxy-2-(4-methoxyphenyl)ethyl]-4-bromobenzene (3af)
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Prepared according to general procedure described above by reacting 4-methoxystyrene (32 L,
0.24 mmol, 1 equiv.), 4-bromophenyldiazonium tetrafluoroborate (194 mg, 0.72 mmol, 3 equiv.)
with methanol (0.8 mL, 83 equiv.). The title compound was purified by column chromatography
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with silica gel using 1% EtOAc in n-hexane as brown oil (64 mg, 83%). H NMR (400 MHz,
CDCl3, 298 K) δ (ppm) 7.34 (d, J = 8.0 Hz, 2H), 7.12 (d, J = 8.0 Hz, 2H), 6.95 (d, J = 8.0 Hz, 2H),
6.86 (d, J = 8.0 Hz, 2H), 4.22 (t, 1H), 3.81 (s, 3H), 3.16 (s, 3H), 3.083.02 (dd, J = 16.0, 8.0 Hz,
1H), 2.82 (dd, J = 16.0, 8.0 Hz, 1H). 13C {1H} NMR (100 MHz, CDCl3, 298 K) δ (ppm) 159.1,
137.5, 133.1, 131.2, 131.1, 128.0, 120.0, 113.7, 84.2, 56.5, 55.2, 44.1. HRMS m/z calcd for
C16H17BrNaO2 (M+Na): 343.0304, found 343.0289.
1-[2-Methoxy-2-(4-methoxyphenyl)ethyl]-3,5-dichlorobenzene (3ag)
Prepared according to general procedure described above by reacting 4-methoxystyrene (32 L,
0.24 mmol, 1 equiv.), 3,5-dichlorophenyldiazonium tetrafluoroborate (187 mg, 0.72 mmol, 3
equiv.) with methanol (0.8 mL, 83 equiv.). The title compound was purified by column
chromatography with silica gel using 1% EtOAc in n-hexane as brown oil (54 mg, 72%). 1H NMR
(400 MHz, CDCl3, 298 K) δ (ppm)7.19 (s, 1H), 7.15 (d, J = 8 Hz, 2H), 7.01 (s, 2H ), 6.88 (d, J =
8.0 Hz, 2H), 4.24 (dd, J = 8.0, 4.0 Hz, 1H), 3.82 (s, 3H), 3.15 (s, 3H), 3.02 (dd, J = 16.0, 8.0 Hz,
1H), 2.80 (dd, J = 12.0, 4.0 Hz, 1H). 13C {1H} NMR (100 MHz, CDCl3, 298 K) δ (ppm) 159.3,
142.0, 134.3, 132.8, 127.9, 127.8, 126.3, 113.8, 83.6, 56.5, 55.2, 44.1. HRMS m/z calcd for
C15H13Cl2O (M-MeOH+H): 279.0343, found 279.0345.
1-[2-Methoxy-2-(4-methoxyphenyl)ethyl]-4-nitrobenzene (3ah)
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Prepared according to general procedure described above by reacting 4-methoxystyrene (32 L,
0.24 mmol, 1 equiv.), 4-nitrophenyldiazonium tetrafluoroborate (171 mg, 0.72 mmol, 3 equiv.)
with methanol (0.8 mL, 83 equiv.). The title compound was purified by column chromatography
with silica gel using 1% EtOAc in n-hexane as yellow solid (58 mg, 84%). Data are in accordance
with previous literature reports.12 1H NMR (400 MHz, CDCl3, 298 K) δ (ppm) 8.09 (d, J = 8.0 Hz,
2H), 7.24 (d, J = 8.0 Hz, 2H), 7.12 (d, J = 8.0 Hz, 2H), 6.86 (d, J = 8.0 Hz, 2H), 4.29 (m, 1H), 3.81
(s, 3H), 3.20-3.15 (m, 4H), 2.98 (dd, J = 12.0 Hz, 4.0 Hz, 1H). 13C {1H} NMR (100 MHz, CDCl3,
298 K) δ (ppm) 159.3, 146.5, 146.4, 132.6, 130.3, 127.9, 123.3, 113.8, 83.7, 56.5, 55.2, 44.5.
HRMS m/z calcd for C16H17NNaO4 (M+Na): 310.1050, found 310.1052.
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1-[2-Methoxy-2-(4-methoxyphenyl)ethyl]-4-methylbenzene (3ai)
Prepared according to general procedure described above by reacting 4-methoxystyrene (32 L,
0.24 mmol, 1 equiv.), 4-methylphenyldiazonium tetrafluoroborate (148 mg, 0.72 mmol, 3 equiv.)
with methanol (0.8 mL, 83 equiv.). The title compound was purified by column chromatography
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with silica gel using 1% EtOAc in n-hexane as pale yellow oil (33 mg, 52%). H NMR (400 MHz,
CDCl3, 298 K) δ (ppm) 7.17 (d, J = 8.6 Hz, 2H), 7.06 (d, J = 8.0 Hz, 2H), 7.00 (d, J = 8.0 Hz, 2H),
6.88 (d, J = 13.0Hz, 2H), 4.27 (t, J = 16.0 Hz, 1H), 3.82 (s, 3H), 3.18 (s, 3H), 3.10 (dd, J = 12.0,
8.0 Hz, 1H), 2.85 (dd, J = 16.0, 8.0 Hz, 1H), 2.32 (s, 3H). 13C {1H} NMR (100 MHz, CDCl3, 298
K) δ (ppm) 159.0, 135.5, 133.7, 129.3, 128.7, 128.0, 127.7, 113.6, 84.7, 56.5, 55.2, 44.3. HRMS
m/z calcd for C17H20NaO2 (M+Na) :279.1356, found 279.1365.
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1-[2-Methoxy-2-(4-methoxyphenyl)ethyl]-4-methoxybenzene (3aj)
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Prepared according to general procedure described above by reacting 4-methoxystyrene (32 L,
0.24 mmol, 1 equiv.), 4-methoxyphenyldiazonium tetrafluoroborate (160 mg, 0.72 mmol, 3 equiv.)
with methanol (0.8 mL, 83 equiv.). The title compound was purified by column chromatography
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with silica gel using 1% EtOAc in n-hexane as yellow solid (36 mg, 55%). m.p.: 63.4 °C. H
NMR (400 MHz, CDCl3, 298 K) δ (ppm) 7.13 (d, J = 8.0 Hz, 2H), 6.99 (d, J = 8.0 Hz, 2H), 6.85
(d, J = 8.0 Hz, 2H), 6.77 (d, J = 8.0 Hz, 2H), 3.81 (s, 3H), 3.77 (s, 3H), 3.17 (s, 3H), 3.06 (dd, J =
12.0, 4.0 Hz, 1H), 2.81 (dd, J = 16.0, 8.0 Hz, 1H). 13C {1H} NMR (100 MHz, CDCl3, 298 K) δ
(ppm) 159.1, 158.0, 133.7, 130.7, 130.5, 128.1, 113.7, 113.5, 84.9, 56.6, 55.3, 55.3, 43.9. HRMS
m/z calcd for C17H20NaO3 (M+Na): 295.1305, found 295.1281.
1-[2-Methoxy-2-(4-methylphenyl)ethyl]benzene (3ba)
Prepared according to general procedure described above by reacting 4-methylstyrene (32 L, 0.24
mmol, 1 equiv), phenyldiazonium tetrafluoroborate (138 mg, 0.72 mmol, 3 equiv) with methanol
(0.8 mL, 83 equiv). The title compound was purified by column chromatography with silica gel
using 0.1% EtOAc in n-hexane as a pale yellow solid (32 mg, 59%). Data are in accordance with
previous literature reports.13 1H NMR (400 MHz, CDCl3, 298 K) δ (ppm) 7.32–7.17 (m, 9H), 4.36
(m, 1H), 3.24 (s, 3H), 3.17 (dd, J = 16.0, 8.0 Hz, 1H), 2.94 (dd, J = 16.0, 8.0 Hz, 1H), 2.41 (s, 3H).
13C {1H} NMR (100 MHz, CDCl3, 298 K) δ (ppm) 138.7, 138.6, 137.2, 129.4, 129.0, 128.0, 126.7,
126.1, 84.9, 56.6, 44.8, 21.1.
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1-[2-Methoxy-2-(4-methylphenyl)ethyl]-2-fluorobenzene (3bb)
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Prepared according to general procedure described above by reacting 4-methylstyrene (32 L, 0.24
mmol, 1 equiv), 2-fluorophenyldiazonium tetrafluoroborate (155 mg, 0.72 mmol, 3 equiv) with
methanol (0.8 mL, 83 equiv). The title compound was purified by column chromatography with
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silica gel using 1% EtOAc in n-hexane as a pale yellow oil (41 mg, 69%). H NMR (400 MHz,
CDCl3, 298 K) δ (ppm) 7.17 – 7.12 (m, 5H), 7.09 – 7.04 (m, 1H), 7.01-6.96 (m, 2H), 4.35 (t, J =
16.0 Hz, 1H), 3.17 (s, 3H), 3.12 (dd, J = 12.0, 8.0 Hz, 1H), 2.93 (dd, J = 12.0, 4.0 Hz, 1H), 2.34
(s, 3H). 13C {1H} NMR (100 MHz, CDCl3, 298 K) δ (ppm) 161.3 (d, J = 244.0 Hz), 138.4, 137.3,
131.9 (d, J = 5.0 Hz), 129.0, 127.8 (d, J = 8.0 Hz), 126.6, 125.5 (d, J = 15.0 Hz), 123.6 (d, J = 3.0
Hz), 115.0 (d, J = 22.0 Hz), 83.4, 56.7, 37.9, 21.1. 19F {1H} NMR (470 MHz, CDCl3, 298 K) δ
(ppm) 118.3. HRMS m/z calcd for C16H17FNaO (M+Na): 267.1156, found 267.1153.
1-[2-Methoxy-2-(4-methylphenyl)ethyl]-3-bromobenzene (3bd)
Prepared according to general procedure described above by reacting 4-methylstyrene (32 L, 0.24
mmol, 1 equiv), 3-bromophenyldiazonium tetrafluoroborate (194 mg, 0.72 mmol, 3 equiv) with
methanol (0.8 mL, 83 equiv). The title compound was purified by column chromatography with
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silica gel using 1% EtOAc in n-hexane as brown oil (55 mg, 75%). H NMR (400 MHz, CDCl3,
298 K) δ (ppm) 7.33 (d, J = 8.0 Hz, 2H), 7.18–7.08 (m, 5H), 7.04 (d, J = 8.0 Hz, 1H), 4.29 (dd, J
= 8.0, 4.0 Hz, 1H), 3.18 (s, 3H), 3.06 (dd, J = 16.0, 8.0 Hz, 1H), 2.85 (dd, J = 12.0, 4.0 Hz, 1H),
2.36 (s, 3H). C {1H} NMR (100 MHz, CDCl3, 298 K) δ (ppm) 141.0, 138.2, 137.4, 132.4, 129.5,
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129.2, 129.1, 128.1, 126.6, 122.1, 84.4, 56.6, 44.4, 21.1. HRMS m/z calcd for C16H17BrNaO
(M+Na): 327.0355, found 327.0356.
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1-[2-Methoxy-2-(4-methylphenyl)ethyl]-4-chlorobenzene (3be)
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Prepared according to general procedure described above by reacting 4-methylstyrene (32 L, 0.24
mmol, 1 equiv), 4-chlorophenyldiazonium tetrafluoroborate (163 mg, 0.72 mmol, 3 equiv) with
methanol (0.8 mL, 83 equiv). The title compound was purified by column chromatography with
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silica gel using 1% EtOAc in n-hexane as brown oil (40 mg, 65%). H NMR (400 MHz, CDCl3,
298 K) δ (ppm) 7.21 (d, J = 8.0 Hz, 2H), 7.16 – 7.11 (m, 4H), 7.04 (d, J = 8.0 Hz, 2H), 4.26 (m,
1H), 3.18 (s, 3H), 3.05 (dd, J = 16.0, 4.0 Hz, 1H), 2.87 (dd, J = 12.0, 4.0 Hz, 1H), 2.36 (s, 3H).
13C {1H} NMR (100 MHz, CDCl3, 298 K) δ (ppm) 138.1, 137.3, 137.0, 131.8, 130.7, 129.0, 128.0,
126.6, 84.5, 56.5, 44.0, 21.1. HRMS m/z calcd for C15H14Cl (M-MeOH+H): 229.0784, found
229.0751.
1-[2-Methoxy-2-(4-methylphenyl)ethyl]-4-bromobenzene (3bf)
Prepared according to general procedure described above by reacting 4-methylstyrene (32 L, 0.24
mmol, 1 equiv), 4-bromophenyldiazonium tetrafluoroborate (194 mg, 0.72 mmol, 3 equiv) with
methanol (0.8 mL, 83 equiv). The title compound was purified by column chromatography with
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silica gel using 1% EtOAc in n-hexane as brown oil (50 mg, 68%). H NMR (400 MHz, CDCl3,
298 K) δ (ppm) 7.35 (d, J = 8.0 Hz, 2H), 7.13 (m, 4H), 6.98 (d, J = 8.0 Hz, 2H), 4.24 (m, 1H), 3.16
(s, 3H), 3.04 (dd, J = 12.0, 8.0 Hz, 1H), 2.83 (dd, J = 16.0, 8.0 Hz, 1H), 2.35 (s, 3H). C {1H}
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NMR (100 MHz, CDCl3, 298 K) δ (ppm) 138.2, 137.6, 137.4, 131.2, 131.1, 129.1, 126.7, 120.0,
84.5, 56.6, 44.1, 21.1. HRMS m/z calcd for C15H14Br (M-MeOH+H): 273.0279, found 273.0272.
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1-[2-Methoxy-2-(4-methylphenyl)ethyl]-3,5-dichlorobenzene (3bg)
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Prepared according to general procedure described above by reacting 4-methylstyrene (32 L, 0.24
mmol, 1 equiv), 3,5-dichlorophenyldiazonium tetrafluoroborate (187 mg, 0.72 mmol, 3 equiv)
with methanol (0.8 mL, 83 equiv). The title compound was purified by column chromatography
with silica gel using1% EtOAc in n-hexane as brown oil (48 mg, 68%). 1H NMR (400 MHz,
CDCl3, 298 K) δ (ppm) 7.21 – 7.12 (m, 5H), 7.04 (d, J = 4.0 Hz, 2H), 4.26 (dd, J = 8.0, 4.0 Hz,
1H), 3.17 (s, 3H), 3.01 (dd, J = 12.0, 8.0 Hz, 1H), 2.81 (dd, J = 12.0, 4.0 Hz, 1H), 2.36 (s, 3H).
13C {1H} NMR (100 MHz, CDCl3, 298 K) δ (ppm) 142.1, 137.9, 137.6, 134.3, 129.2, 127.9, 126.5,
126.4, 84.0, 56.7, 44.2, 21.1. HRMS m/z calcd for C15H13Cl2 (M-MeOH+H): 263.0394, found
263.0401.
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1-[2-Methoxy-2-(4-methylphenyl)ethyl]-4-nitrobenzene (3bh)
Prepared according to general procedure described above by reacting 4-methylstyrene (32 L, 0.24
mmol, 1 equiv), 4-nitrophenyldiazonium tetrafluoroborate (171 mg, 0.72 mmol, 3 equiv) with
methanol (0.8 mL, 83 equiv). The title compound was purified by column chromatography with
silica gel using1% EtOAc in n-hexane as colorless oil (43 mg, 63%). Data are in accordance with
previous literature reports.12 1H NMR (400 MHz, CDCl3, 298 K) δ (ppm) 8.08 (d, J = 12.0 Hz,
2H), 7.25 (d, J = 8.0 Hz, 2H), 7.14-7.08 (m, 4H), 4.30 (m, 1H), 3.18-3.13 (m, 4H), 3.00 (m, 1H),
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2.34 (s, 3H). C {1H} NMR (100 MHz, CDCl3, 298 K) δ (ppm) 146.5, 146.4, 137.6, 137.6, 130.3,
129.1, 126.5, 123.2, 83.9, 56.6, 44.5, 21.1.
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1-(2-Methoxy-2-phenylethyl)-4-nitrobenzene (3ch)
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Prepared according to general procedure described above by reacting styrene (28L, 0.24 mmol,
1 equiv), 4-nitrophenyldiazonium tetrafluoroborate (171 mg, 0.72 mmol, 3 equiv) with methanol
(0.8 mL, 83 equiv). The title compound was purified by column chromatography with silica gel
using1% EtOAc in n-hexane as a yellow solid (24 mg, 38%). Data are in accordance with previous
literature reports.13 1H NMR (400 MHz, CDCl3, 298 K) δ (ppm) 8.09 (d, J = 8.0 Hz, 2H), 7.33 –
7.20 (m, 7H), 4.34 (m, 1H), 3.20–3.15 (m, 4H), 3.00 (dd, J = 12.0, 4.0 Hz, 1H). 13C {1H} NMR
(100 MHz, CDCl3, 298 K) δ (ppm) 146.3, 146.2, 140.7, 130.4, 128.5, 128.0, 126.6, 123.3, 84.2,
56.8, 44.5.
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1-[2-Methoxy-2-(2-methylphenyl)ethyl]-4-nitrobenzene (3dh)
Prepared according to general procedure described above by reacting 2-methylstyrene (31 L, 0.24
mmol, 1 equiv), 4-nitrophenyldiazonium tetrafluoroborate (171 mg, 0.72 mmol, 3 equiv) with
methanol (0.8 mL, 83 equiv). The title compound was purified by column chromatography with
silica gel using1% EtOAc in n-hexane as a palebrownish oil (33 mg, 51%). Data are in accordance
with previous literature reports.12 1H NMR (400 MHz, CDCl3, 298 K) δ (ppm) 8.08 (d, J = 8.0
Hz, 2H), 7.31 (d, J = 8.0 Hz, 1H), 7.26-7.15 (m, 4H), 7.10 (d, J = 8.0 Hz, 1H), 4.59 (dd, J = 8.0
Hz, 8.0 Hz, 1H), 3.14 (s, 3H), 3.08 (dd, J = 16.0 Hz, 8.0 Hz, 1H), 2.95 (dd, J = 12.0 Hz, 4.0 Hz,
1H), 2.20 (s, 3H). 13C {1H} NMR (125 MHz, CDCl3, 298 K) δ (ppm) 146.7, 146.5, 138.8, 135.2,
130.5, 130.3, 127.5, 126.4, 125.9, 123.3, 80.5, 56.7, 43.5, 19.0.
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1-[2-Methoxy-2-(2,5-dimethylphenyl)ethyl]-4-nitrobenzene (3eh)
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Prepared according to general procedure described above by reacting 2,5-dimethylstyrene (35L,
0.24 mmol, 1 equiv), 4-nitrophenyldiazonium tetrafluoroborate (171 mg, 0.72 mmol, 3 equiv) with
methanol (0.8 mL, 83 equiv). The title compound was purified by column chromatography with
silica gel using1% EtOAc in n-hexane as a pale yellow solid (35 mg, 51%). m.p.: 5052 °C. 1H
NMR (400 MHz, CDCl3, 298 K) δ (ppm) 8.11 (d, J = 8.0 Hz, 2H), 7.30 (d, J = 8.0 Hz, 2H), 7.17
(s, 1H), 7.01 (s, 1H), 4.58 (dd, J = 8.0, 4.0 Hz, 1H), 3.16 (s, 3H), 3.123.07 (dd, J = 12.0, 8.0 Hz,
1H), 2.95 (dd, J = 12.0, 4.0 Hz, 1H), 2.33 (s, 3H), 2.18 (s, 3H). 13C {1H} NMR (100 MHz, CDCl3,
298 K) δ (ppm) 146.7, 146.6, 138.6, 135.9, 132.1, 130.4, 130.2, 128.2, 126.3, 123.3, 80.5, 56.7,
43.6, 21.1, 18.5. HRMS m/z calcd for C17H19NNaO3 (M+Na): 308.1257, found 308. 1272.
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1-[2-Methoxy-2-(4-tert-butylphenyl)ethyl]-4-nitrobenzene (3fh)
Prepared according to general procedure described above by reacting 4-tert-butylstyrene (44 L,
0.24 mmol, 1 equiv), 4-nitrophenyldiazonium tetrafluoroborate (171 mg, 0.72 mmol, 3 equiv) with
methanol (0.8 mL, 83 equiv). The title compound was purified by column chromatography with
silica gel using1% EtOAc in n-hexane as yellow crystalline solid (51 mg, 68%). Data are in
accordance with previous literature reports.12 1H NMR (400 MHz, CDCl3, 298 K) δ (ppm) 8.10
(d, J = 8.0 Hz, 2H), 7.36 (d, J = 8.0 Hz, 2H), 7.29 (d, J = 8.0 Hz, 2H), 7.17 (d, J = 4.0 Hz, 2H),
4.32 (dd, J = 4.0 Hz, 4.0 Hz, 1H), 3.18-3.14 (m, 4H), 2.99 (dd, J = 12.0 Hz, 4.0 Hz, 1H), 1.33 (s,
9H). 13C {1H} NMR (100 MHz, CDCl3, 298 K) δ (ppm) 151.0, 146.7, 146.6, 137.7, 130.3, 126.3,
125.4, 123.2, 83.9, 56.7, 44.5, 34.5, 31.3. HRMS m/z calcd for C19H23NNaO3 (M+Na): 336.1570,
found 336.1557.
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1-[2-Methoxy-2-(4-tert-butylphenyl)ethyl]-3-chlorobenzene (3fc)
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Prepared according to general procedure described above by reacting 4-tert-butylstyrene (44 L,
0.24 mmol, 1 equiv), 3-chlorophenyldiazonium tetrafluoroborate (163 mg, 0.72 mmol, 3 equiv)
with methanol (0.8 mL, 83 equiv). The title compound was purified by column chromatography
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with silica gel using1% EtOAc in n-hexane as orange oil (55 mg, 76%). H NMR (400 MHz,
CDCl3, 298 K) δ (ppm) 7.32 (d, J = 12 Hz, 2H), 7.15 – 7.13 (m, 4H), 7.08 (s, 1H), 6.98 (t, 1H),
4.26 (dd, J = 8.0, 4.0 Hz, 1H), 3.15 (s, 3H), 3.02 (dd, J = 12.0, 8.0 Hz, 1H), 2.82 (dd, J = 16.0, 4.0
Hz, 1H), 1.30 (s, 9H). 13C {1H} NMR (100 MHz, CDCl3, 298 K) δ (ppm) 150.7, 140.9, 138.2,
133.7, 129.5, 129.2, 127.6, 126.3, 126.3, 125.2, 84.3, 56.8, 44.4, 34.5, 31.4. HRMS m/z calcd for
C19H23ClNaO (M+Na): 325.1330, found 325.1332.
1-[2-Methoxy-2-(4-tert-butylphenyl)ethyl]-3-bromobenzene (3fd)
Prepared according to general procedure described above by reacting 4-tert-butylstyrene (44 L,
0.24 mmol, 1 equiv), 3-bromophenyldiazonium tetrafluoroborate (194 mg, 0.72 mmol, 3 equiv)
with methanol (0.8 mL, 83 equiv). The title compound was purified by column chromatography
with silica gel using1% EtOAc in n-hexane as a pale yellow oil (58 mg, 72%). Data are in
accordance with previous literature reports.12 1H NMR (400 MHz, CDCl3, 298 K) δ (ppm) 7.35
(d, J = 8.0 Hz, 2H), 7.32 (td, J = 8.0 Hz, 4.0 Hz, 1H), 7.25 (t, 1H), 7.16 (d, J = 8.0 Hz, 2H), 7.11-
7.06 (m, 2H), 4.28 (dd, J = 8.0 Hz, 4.0 Hz, 1H), 3.18 (s, 3H), 3.03 (dd, J = 12.0 Hz, 8.0 Hz, 1H),
2.84 (dd, J = 12.0 Hz, 4.0 Hz, 1H), 1.33 (s, 9H). 13C {1H} NMR (100 MHz, CDCl3, 298 K) δ
(ppm) 150.7, 141.2, 138.2, 132.4, 129.5, 129.2, 128.1, 126.3, 125.2, 122.1, 84.4, 56.8, 44.4, 34.5,
31.4.
29
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