Visible Light Promoted, Catalyst-Free Radical Carbohydroxylation and Carboetherification under Mild Biomimetic Conditions

Article abstract of DOI:10.1002/chem.202004234

Metal and catalyst-free carbohydroxylations and carboetherifications at room temperature have been achieved by a combination of beneficial factors including high aryl diazonium concentration and visible light irradiation. The acceleration of the reaction by visible light irradiation is particularly remarkable against the background that neither the aryldiazonium salt nor the alkene show absorptions in the respective range of wavelength. These observations point to weak charge transfer interactions between diazonium salt and alkene, which are nevertheless able to considerably influence the reaction course. As highly promising perspective, many more aryldiazonium-based radical arylations might benefit from simple light irradiation without requiring a photocatalyst or particular additive.

Full text of DOI:10.1002/chem.202004234

Accepted Article
Accepted Article
Title: Visible light promoted, catalyst-free radical carbohydroxylation
and carboetherification under mild biomimetic conditions
Authors: Markus Rolf Heinrich, Lisa-Marie Altmann, Viviane Zantop,
Pia Wenisch, and Nina Diesendorf
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
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published online in Early View as soon as possible and may be different
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content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.202004234
Link to VoR: https://doi.org/10.1002/chem.202004234
01/2020

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Visible light promoted, catalyst-free radical carbohydroxylation
and carboetherification under mild biomimetic conditions
Lisa-Marie Altmann,[a] Viviane Zantop,[a] Pia Wenisch,[a] Nina Diesendorf,[a] Markus R. Heinrich*[a]
Dedication ((optional))
[a]
M. Sc. L-M. Altmann, V. Zantop, B. Sc. P. Wenisch, M. Sc. N. Diesendorf, Prof. Dr. M. R. Heinrich
Department of Chemistry and Pharmacy, Pharmaceutical Chemistry
Friedrich-Alexander-Universität Erlangen-Nürnberg
Nikolaus-Fiebiger-Str. 10, 91058 Erlangen
E-mail: markus. heinrich@fau.de
Supporting information for this article is given via a link at the end of the document.
Abstract: Metal and catalyst-free carbohydroxylations and
carboetherifications at room temperature have been achieved by a
combination of beneficial factors including high aryl diazonium
concentration and visible light irradiation. The acceleration of the
reaction by visible light irradiation is particularly remarkable against
the background that neither the aryldiazonium salt nor the alkene
show absorptions in the respective range of wavelength. These
observations point to weak charge transfer interactions between
diazonium salt and alkene, which are nevertheless able to
considerably influence the reaction course. As highly promising
perspective, many more aryldiazonium-based radical arylations
Following the reductive formation of an aryl radical 2 from the
diazonium salt 1, addition to the alkene 3 gives the central alkyl
intermediate 4. While in classical reactions, the C-O bond in 5 is
formed via ligand transfer from a copper complex[10] or by
trapping of radical 4 by a persistent oxygen-centered radical
such as 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO),[11] C-O
bond formation may also be achieved via intermediate oxidation
of radical 4 to cation 6. Not surprisingly, the radical polar cross-
over pathway[12] is highly dependent on the stabilization of cation
6 (e.g. R = aryl, Oalkyl),[13] whereat the final carbooxygenation
product 5 then arises from the attack of an oxygen-centered
might benefit from simple light irradiation without requiring
photocatalyst or particular additive.
a
nucleophile.
Remarkably,
the
scope
of
Meerwein
carbooxygenations could be significantly broadened by
exploiting the radical polar cross-over pathway, as such simple
compounds as water or aliphatic alcohols may now be used for
C-O bond formation, and thus to determine the nature of the OR’
group in 5.[14]
Introduction
Within our recent research in the field of Meerwein arylation
chemistry,[15] a novel variant could be developed, in which the
carbohydroxylation of styrenes was achieved in metal- and
catalyst-free reactions under thermal conditions (70 °C).[16] The
facts that no additives besides the diazonium salt and the
styrene are required, and that the solvent mixture already
comprises water to introduce the hydroxyl group, are important
pre-requisites to further develop this reaction type towards an
arylation under biomimetic conditions. Regarding so far
proposed biocompatible arylations,[17] there is still room for
improvement, as many of these transformations have either to
be conducted at elevated temperatures, in a non-natural pH
environment, or they comprise non-natural additives.[17] In this
work, it will be shown which particular and partially surprising
effects can be exploited to conduct the carbohydroxylation at
room temperature, and how these findings can be extended
Radical alkene functionalizations[1] have become increasingly
popular over the last two decades, especially due to the
development of
a
great variety of novel metal-free,[2]
photocatalyzed[3] or even catalyst-free reactions.[4] An important
subgroup
within
this
general
reaction
type
are
carbooxygenations,[5] whereat a carbon moiety and an oxygen-
centered functional group are attached to the original alkene unit.
Such
transformations,
which
include
radical
carbohydroxylations[6] and carboetherifications[7] as most
prominent examples, can proceed via two major reaction
mechanisms. In Scheme 1, this is shown for intermolecular
Meerwein-type[8,9] carbooxygenations, where an aryldiazonium
salt is used as radical precursor.
towards
a
particularly mild, metal- and catalyst-free
carboetherification.
Results and Discussion
To assess how the previously developed carbohydroxylation
could be conducted under biomimetic conditions, particularly at
room temperature, a closer look at the underlying mechanism is
helpful (Scheme 2). As the initiation step from diazonium ion 1 to
radical 2 will be much slower at room temperature than at
Scheme
carbooxygenations.
1.
Reaction
mechanisms
for
Meerwein-type
radical
1
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70°C,[18] we thought to evaluate whether this drawback can be
counterbalanced by visible light irradiation. Although none of the
reactants shows absorptions in the range of 450-475 nm,
increased initiation might nevertheless occur via the formation of
weak charge-transfer complexes.[19]
tetrafluoroborate salt 1a in the carbohydroxylation (see
Supporting Information).
The beneficial effect of performing the carbohydroxylation under
visible light irradiation (450-475 nm) was confirmed in additional
experiments with 4-fluoro-, 3-bromo- and 4-bromophenyl-
diazonium tetrafluoroborate 1b-d under otherwise identical
conditions (Figure 1). Having observed that visible light
irradiation raises the temperature of the reaction mixture (23 °C)
by around 3 °C, we further conducted a series of control
experiments at a slightly further increased temperature of 28 °C
to exclude that the accelerating effect attributed to visible light
irradiation would be solely caused by the temperature effect.
Scheme 2. Mechanistic background of the carbohydroxylation of styrenes.
In addition, the chain propagation is likely to be improved by a
faster or even at once addition of the diazonium salt to the
reaction mixture, given that the homocoupling of radical 2 to
diazonium ion 1[20] to give 7 remains slower than the desired
addition of aryl radical 2 to styrene 3.[21] The results of selected
preliminary experiments are summarized in Table 1.
Table 1. Optimization of reaction conditions at room temperature.
entry
conditions
yield 5a[a]
1%
1
2
3
4
5
6
darkness, N2, 1 h (23°C)
darkness, N2, 3 h (23 °C)
darkness, N2, 19 h (23 °C)
LED, N2, 1 h (26 °C)
20%
Figure 1. Comparison of the reaction course under blue LED irradiation with
reactions in darkness.
73%
72%
Comparing the yields of 5a-d under irradiation (blue) and in
darkness (orange and grey) after one hour, the strongest relative
effects were found for 4-chloro, 4-fluoro and 4-bromo
substitution 5a-c, where the yield under irradiation exceeded the
one in darkness by factors of 34 to 72 (at 23 °C) and 2.6 to 4.9
(at 28 °C), respectively. The reaction with the 3-
bromophenyldiazonium salt 5d was found to be the fastest in
darkness, which points to a somehow higher reactivity of this
particular diazonium ion (see below) or related to mechanism,
possibly also a more effective chain propagation step (c.f.
Scheme 2) under the present conditions. Regarding the final
yield after 19 h, the largest increase upon irradiation was
observed for the 4-fluoro-substituted derivative 5b. In a further
control experiment on the effect of irradiation, the reaction
mixture containing 1a and 3a (to give 5a) was cooled to 10°C.
LED, N2, 3 h (26 °C)
LED, N2, 19 h (26 °C)
79%
79%
[a] Yields determined by 1H-NMR using 1,4-dimethoxybenzene as internal
standard.
While the “at once addition” of the diazonium salt 1a to the
reaction mixture was shown to be feasible, it still led to a
comparably long reaction times (entries 1-3). Additional
irradiation with blue LEDs (450-475 nm) then resulted in a
remarkable increase of the reaction rate (entries 4-6). The
strongest relative effect was found at a reaction time of 1 hour
(c.f. entries 1 and 4). Additional attempts with the corresponding
diazonium chloride pointed to
a higher reactivity of the
2
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While almost no formation of 5a (1%) was observed at 23°C
after 1 h (in the dark), and the reaction should be even slower at
10°C, irradiation of this particular mixture now gave 6% of 5a
after 1 h, thereby underlining the benefit of irradiation.
To get insights why particular reactions might initially benefit
more from irradiation than others, UV spectra of the diazonium
salts 1a-d, of α-methylstyrene (3a), and of the four individual
reaction mixtures were recorded (Figure 2). Due to the very
weak absorptions of the reactants 1a-d and 3a, the spectra
could be obtained at comparably high concentrations, which
were identical to those in the real reaction mixtures (Table 1,
Figure 1).
Figure 3. Decomposition of the diazonium salt 1a upon irradiation at 450-475
nm with no additive, benzene or α-methylstyrene (3a).
With no additive being present, 1a decomposes slowly. The
addition of benzene (6 equiv.) was already able to slightly
accelerate the decay, which points to a weak interaction with the
diazonium ion, and which is in agreement with earlier results.[19a]
Due to a most likely stronger interaction, and accelerated by the
chain mechanism (Scheme 2), the by far fastest consumption of
1a was observed in combination with styrene 3a (6 equiv.).
As the overall reaction rate of the carbohydroxylation not only
depends on initiation, but also on the chain transfer step
(Scheme 2), we further investigated the four diazonium salts 1a-
d using Differential Pulse Voltammetry (DPV) (Figure 4). The
main question thereby was whether 1a-d might differ in their
reduction potentials, which could explain facilitated initiation as
well as chain transfer.
Figure 2. UV-Vis spectra of 1a-d, α-methylstyrene (3a) and the 4 related
reaction mixtures.
As expected, the formation of a strong CT complex between one
of the diazonium ions 1a-d and 3a could not be observed for any
of the four combinations. As even minor differences between the
reactions are hardly detectable, it appears not to be possible to
directly correlate the stronger acceleration in the reactions to 5a-
c to an increased absorption of the particular reaction mixture.
Most importantly, all measured absorptions in the visible
irradiation range from 450 to 475 nm are very weak, as indicated
by the very low ε values determined for the reaction mixtures
comprising a diazonium salt from 1a-d and styrene 3a (1a/3a:
1.50-0.88 M-1cm-1, 1b/3a: 3.92-1.46 M-1cm-1, 1c/3a: 1.88-0.97 M-
1cm-1, 1d/3a: 4.83-2.29 M-1cm-1). On this basis, the observed
sensitivity of the carbohydroxylation to irradiation is surprising,
and most likely due to an increased initiation rate via very weak,
hardly detectable, but still effective intermolecular CT
interactions.[19a]
Figure 4. Differential pulse voltammetry measurements for 1a-d.
The results from these experiments demonstrate that the
reduction of the 3-bromo derivative 1d (0.51 V) is slightly easier
than that of the three 4-substituted diazonium ions 1a-1c (0.34
V, 0.36 V, 0.34 V, respectively). The reaction with 1d might thus
benefit from a facilitated initiation and chain transfer, which is in
agreement with Figure 1, where 1d shows the fastest reactions
in the dark at 23°C and at 28°C. The fact that among the
“electrochemically identical” diazonium ions 1a-c, the fastest
arylation of styrene 3a was observed for the 4-chloro derivative
1a, can be a hint to a slightly more effective CT interaction of
this particular diazonium ion with 3a.
Further support for such interactions could be obtained from
three experiments, in which diazonium salt 1a was once
irradiated in the solvent mixture without further additive, then in
the presence of benzene (6 equiv.) and finally together with the
typical substrate α-methylstyrene (3a) (Figure 3).
3
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With insights into the mechanism and optimized conditions now
available (Table 1), we continued with an evaluation of the
substrate scope (Scheme 3). Within this study, we focused on
the variation of the diazonium ion, since this is known as the
more critical component regarding initiation and chain transfer,
and thus the overall reaction course.[16]
diazonium
ion
would
significantly
reduce
its
free
concentration.[15c]
Regarding the results from further reactions combining
irradiation and the presence of potassium acetate, it turned out
that upon variation of the diazonium salt (Scheme 4, upper part),
most yields were slightly improved compared to the base-free
conditions (Scheme 3), with the only exception of the 4-fluoro
derivative 5b. This deviation can however be rationalized by the
low stability of the 4-fluorophenyl diazonium ion under less
acidic conditions, as it may undergo substitution at the 4-
position.[24]
Scheme 3. Scope of carbohydroxylation at room temperature. Yields
determined after column chromatography. Yields given in brackets determined
by 1H-NMR using 1,4-dimethoxybenzene as internal standard. [c]Reaction
mixture neutralized during work-up and before column chromatography.
Synthetically useful yields were obtained for most diazonium
salts in combination with α-methylstyrene (3a). Only the 4-
methoxy derivative 5h turned out as too unreactive, at which the
low reactivity resulting from donor substitution could not be
overcome by irradiation.[19a] A low yield of 25% was observed for
the functionalization of 1,1-diphenylethene (3b), which can partly
be explained by insufficient solubility and ineffective phase
transfer of the aryl radical.[22]
Scheme 4. Scope of carbohydroxylation in the presence of potassium acetate.
Yields determined after column chromatography;
[a]
Yield determined by 1H-
NMR using 1,4-dimethoxybenzene as internal standard.
Regarding
the
desired
biocompatibility
of
the
carbohydroxylation, measurements of the pH value during the
synthesis of 5a (Scheme 3) revealed that the pH value drops
from an initial value of 3 to values around 1.5 over the reaction
course. While the initially acidic conditions can be attributed to
traces of tetrafluoroboric acid in the diazonium tetrafluoroborate
salt, the increasing acidity during product formation is caused by
the mechanism, which liberates protons (6→5, Scheme 2). This
drawback can however be balanced by the addition of
potassium acetate (1.5 equiv.) to the reaction mixture. For the
synthesis of 5a, the pH value then changes from 6 to 5, and thus
remains in a fully biocompatible region. Moreover, the presence
of potassium acetate led to an even slightly improved yield for
5a (85%) under irradiation and to a yield of 79% from the control
reaction in darkness at 28 °C. The now lower impact of
irradiation can be explained by the basically facilitated aryl
radical formation at higher pH values, so that the effect of
irradiation and the importance of the weak CT interaction is then
reduced. Notably, and besides typical reductants, less acidic
conditions as well as nucleophiles can have a strong influence
on the rate of aryl radical formation from diazonium ions.[18]
Regarding the general mechanism depicted in Scheme 2, and in
agreement with previous studies,[18] we assume that the effect of
potassium acetate, which is a base and nucleophile, will be
largely limited to the initiation step (1→2, Scheme 2). The aryl
radical addition to styrene 3 (2→4, Scheme 2), for which the rate
can be estimated to around 3×108 M-1s-1[23], is unlikely to be
altered significantly by the presence of the acetate. The final
chain transfer step (4→6, Scheme 2) could basically be
influenced if some adduct of the nucleophile (or base) with the
The variations of the styrene (Scheme 4, lower part) not only
show an enlarged scope, but also support the reaction
mechanism depicted in Scheme 2. While the 4-methoxy
substitution on the styrene increases the yield (5k: 84%), the
corresponding 4-nitro derivative does not give any product 5l
due to the strongly destabilizing effect of the nitro group on the
related cation 6 (Scheme 2). In line with that, unsubstituted
styrene leads to a low yield (5n: 15%) due to the lack of the
methyl group, which can to some extent be counterbalanced by
a 4-methoxy substituent (5o: 46%) that again stabilizes the
cation 6. Such significant deviations were not likely to occur if
the mechanism proceeded via some coupling of radical 4 (c.f.
pathway 4→5, Scheme 1). From the absence of dimerization
products related to the stabilized, benzylic radical 4,[25] one can
even conclude that the oxidation step to cation 6 has to be quite
efficient.
Finally, and also directed towards a future application under
biomimetic conditions, we performed the arylation of α-
methylstyrene (3a) with diazonium salt 1a in a reaction mixture
with a higher water content (water/acetonitrile = 1:1, v/v)
(Scheme 5). In a separate experiment, the amount of 3a was
reduced to only one equivalent.
4
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Although the reaction mixture containing 1a and 3a in methanol
and acetonitrile does show even weaker absorptions in the
range from 450 to 475 nm (ε values from 0.86 to 0.38 M-1cm-1)
than in water and acetonitrile (1.50-0.88 M-1cm-1), a remarkable
effect of visible light irradiation was also observed for
carboetherification (Table 2, entries 1-3) in the absence of
potassium acetate. This can be attributed, as for
carbohydroxylation, to a weak but nevertheless effective CT
complexation, resulting in an improved initiation step and an
increased reaction rate. However, the absence of potassium
acetate again leads to an acidic reaction mixture with pH values
ranging from 3 to 1.5 over the reaction course, which results in
the concomitant formation of methanol adduct 9. The fact that a
comparable side reaction with that to 9 was not observed during
carbohydroxylation can be explained by the increased basicity of
water compared to methanol,[28] which is apparently able to
sufficient reduce the acidity in the reaction mixture.
Scheme 5. Carbohydroxylation conducted with higher water content or
reduced amount of styrene 3a. Yields determined by 1H-NMR using 1,4-
dimethoxybenzene as internal standard.
The fact that both reactions provided the desired alcohol 5a in
only slightly lower yields of 78% and 79% (c.f. 5a: 85%, Scheme
4), respectively, further underlines the excellent suitability of α-
methylstyrenes as highly effective aryl radical acceptors for
future
applications.
The
biological
compatibility
of
tetrafluoroborate has been outlined in a number of previous
studies.[26]
With the addition of potassium acetate (entries 4-6), the pH
change over the reaction course was again shifted to a region
between 6 and 5, and the acid-induced formation of 9 was fully
suppressed. As observed for the carbohydroxylation, the less
acidic reaction mixture now basically favors radical formation
from the diazonium ion and the beneficial effect of light
irradiation is thus reduced.
With practicable conditions for carboetherification available, we
turned to evaluate the substrate scope regarding the diazonium
salt and the alcohol (Scheme 6).
Based on the exceptionally mild and biocompatible conditions
now available for the carbohydroxylation, we turned to
investigate whether the novel procedure could also be extended
to carboetherification. As for the previous modification, namely
the addition of potassium acetate, the presence of methanol can
influence the overall mechanism. In contrast to the previously
used nucleophile water, alcohols can enable hydrogen atom
transfer to aryl radicals, which in the case of methanol would
lead to the •CH2OH radical.[18] As this particular radical is known
to be capable of reducing diazonium ions to aryl radicals and
dinitrogen along with the formation of formaldehyde, an
undesired reduction of the diazonium salt to the parent aromatic
compound can basically occur in the presence of alcohols via
these two steps in the sense of a chain reaction.[27]
Results from initial experiments are summarized in Table 2, at
which the optimized conditions from Table 1 (entry 6) were only
varied in the way that water was replaced by methanol, and the
effect of potassium acetate was studied in this early stage.
Table 2. Optimization of reaction conditions for carboetherification.
entry
conditions
yield 8a[a]
yield 9[b]
1
2
3
4
5
6
darkness, 23 °C
darkness, 28 °C
8%
0%
24%
44%
0%
27%
70%
64%
66%
72%
blue LED (26°C)
KOAc (1.5 eq.), darkness, 23 °C
KOAc (1.5 eq.), darkness, 28 °C
KOAc (1.5 eq.), blue LED (26°C)
Scheme 6. Reaction scope of carboetherification. [a]Yields determined after
column chromatography.
0%
0%
Among the four diazonium salts leading to the methyl ethers 8a-
d, only the 4-fluoro derivative gave a moderate yield of 8b
(37%), which is due to the known sensitivity of the 4-fluoro-
phenyldiazonium ion to less acidic conditions (c.f. Scheme 4).[24]
The successful variation of the alcohols included increased
[a]Yields of 8a determined by 1H-NMR using 1,4-dimethoxybenzene as internal
standard based on diazonium salt 1a. [b]Yields of 9 determined by 1H-NMR
using 1,4-dimethoxybenzene as internal standard based on α-methylstyrene
(3a).
5
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chain length and cyclic moieties (8e-i,l), allyl and benzyl alcohol
(8j and 8k) as well protected and unprotected diols (8m and 8n),
and gave yields in the range of 46 to 69%. Allylic and benzylic
positions, which are often troublesome in radical arylations,[29]
are thus well tolerated in the present functionalization. Only
phenol failed to give the desired carboetherification product 8o,
which can be attributed to the fast hydrogen atom transfer from
phenols to highly reactive aryl radicals under non-aqueous
conditions.[30] Particularly remarkable are the successful
reactions with citronellol and geraniol, which provided 8p and 8q
in yields of 60% and 36% respectively. The mild biomimetic
conditions of the carboetherification, which proceeds at room
temperature and in a pH range from 5 to 6, are thus also
applicable to more sensitive alcohols.
device. For UV and UV-vis irradiation a 250 W iron lamp with either black
glass filter (315-420nm) or without filter (315-700nm) was used. For
visible light irradiation a 10 W blue LED lamp was used. Differential pulse
voltammetry was conducted in a classical three-electrode cell from
Deutsche Metrohm GmbH & Co. KG, which was connected to Metrohm
Autolab PGSTAT 101, controlled by NOVA 2.1 software which was
running on a personal computer. A gold electrode was used as a working
electrode and was combined with a platinum sheet (1.0 cm2) which
served as a counter electrode. All potentials are provided relative to a
Ag/AgCl (2 M lithium chloride in ethanol) reference electrode with a
potential of 0.164 V vs SHE at 21±1°C. Spectra were measured in
acetonitrile (LC-MS grade) at 21±1°C with NBu4PF6 (0.1 M) as a
supporting electrolyte and 1a-d (1 mM). Differential pulse voltammetry
was performed with a scan rate of v = 10 mVs−1. All measurements were
done under nitrogen atmosphere.
General Procedures
Conclusion
Aryldiazonium salts (1a-h):
In summary, it has been shown that radical carbohydroxylations
and carboetherifications can be carried out under hitherto
unknown, exceptionally mild and biomimetic conditions. Besides
the fact that no particular catalyst is required, the reactions
further benefit from their feasibility in the absence of non-natural
additives and at ambient temperature. Particularly remarkable is
the accelerating effect of visible light irradiation, which is
surprising as the individual reaction mixtures show only very
weak absorptions in the applied wavelength range from 450 to
475 nm. This accelerating effect was found useful to increase
the initiation rate when the overall conditions enable only slow
initiation, as for example under acidic conditions. This general
observation may be useful for many other aryldiazonium-based
radical arylations, which can possibly be improved through
visible light irradiation although only weak absorptions of the
reaction mixture can be measured. All in all, these new results
pave the way for a successful future application of aryldiazonium
ions in radical reactions under biomimetic conditions and in
biological systems.
Aryldiazonium tetrafluoroborate salts (1a-h) were prepared according to
literature procedures.[31]
Before use of the aryldiazonium tetrafluoroborate salts 1a-h, the
remaining water content was determined by 1H-NMR to correct the actual
amount of the tetrafluoroborate salts for further reactions.
Alkenes 3c-3f:
Alkenes 3c[32], 3d[32], 3e[33], 3f[34] were prepared according to literature
procedures.
General procedure for carbohydroxylation or carboetherification without
base (GP1):
The alkene (3, 6.0 eq.) was dissolved in a mixture of acetonitrile and
water or alcohol (5/1, 5 mL) under nitrogen atmosphere in a reaction tube.
The tetrafluoroborate diazonium salt 1 (1.0 eq.) was dissolved in a
mixture of acetonitrile and water or alcohol (5/1, 4 mL) and added to the
reaction mixture. The reaction was stirred under nitrogen atmosphere
and either under blue LED irradiation, in the dark at 23 °C or 28 °C for 19
h. Water (50 mL) was added to the mixture and it was extracted with
diethylether (3 x 20 mL). The combined organic phases were dried over
sodium sulfate and the solvent was removed under reduced pressure.
For NMR analysis, 1,4-dimethoxybenzene (69 mg, 0.5 mmol) was added
and dissolved in CDCl3.
Experimental Section
General Experimental
General procedure for carbohydroxylation or carboetherification with
base (GP2):
Solvents and reagents were obtained from commercial sources and used
1
as received. H NMR and 13C NMR spectra were recorded using Bruker
Potassium acetate (1.5 eq.) was added to a reaction tube and the tube
was set under nitrogen atmosphere. The alkene (3, 6.0 eq.) was
dissolved in a mixture of acetonitrile and water or alcohol (5/1, 5 mL) and
added to the reaction. The tetrafluoroborate diazonium salt 1 (1.0 eq.)
was dissolved in a mixture of acetonitrile and water or alcohol (5/1, 4 mL)
and added to the reaction mixture. The reaction was stirred under
nitrogen atmosphere and either under blue LED irradiation, in the dark at
23 °C or 28 °C for 19 h. Water (50 mL) was added to the mixture and it
was extracted with diethylether (3 x 20 mL). The combined organic
phases were dried over sodium sulfate and the solvent was removed
under reduced pressure.
Avance 400 MHz (13C: 101 MHz), and Bruker Avance 600 MHz (13C:
151 MHz) spectrometers. For 1H NMR spectra, CDCl3, CD3CN, D2O,
DMSO were used as solvents referenced to TMS (0 ppm), CDCl3 (7.26
ppm), CD3CN (1.94 ppm), D2O (4.79 ppm), DMSO (2.50 ppm). Chemical
shifts are in parts per million (ppm). Coupling constants are reported in
hertz (Hz). The following abbreviations are used for the description of
signals: s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), bs
(broad singlet). 13C NMR spectra were recorded in CDCl3, CD3CN and
MeOH using CDCl3 (77.0 ppm), CD3CN (118.3 ppm) and MeOH (49.0
ppm) as standard. Chemical shifts are reported in parts per million (ppm).
Mass spectra were recorded using electron spray ionization (ESI) and a
sector field mass analyzer or time of flight (TOF) for HRMS
measurements. Analytical TLC was carried out on Merck silica gel plates
using short wave (254 nm) UV light to visualize components. Silica gel
(Kieselgel 60, 40-63mm, Merck) was used for flash column
chromatography. UV-vis spectra were recorded on a Specord 200 Plus
For NMR analysis, 1,4-dimethoxybenzene (69 mg, 0.5 mmol) was added
and dissolved in CDCl3.
Synthetic procedure and characterization data
6
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1-(4-Chlorophenyl)-2-phenylpropan-2-ol (5a). a) Compound 5a was
prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a, 226 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and water
according to GP1 under blue LED irradiation. The crude product was
purified via column chromatography (isohexane/ ethyl acetate : 6/1 
4/1) to give 5a (191 mg, 0.77 mmol, 77%) as a yellow oil. b) Compound
5a was prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a,
226 mg, 1.00 mmol) and α-methylstyrene (3a, 0.78 mL, 6.00 mmol)
according to GP2 under blue LED irradiation. The crude product was
purified via column chromatography (100% isohexane  isohexane/
ethyl acetate : 4/1) to give 5a (209 mg, 0.85 mmol, 85%) as a yellow oil.
c) Compound 5a was prepared from 4-chlorophenyl diazonium
tetrafluoroborate (1a, 226 mg, 1.00 mmol) and α-methylstyrene (3a, 0.78
mL, 6.00 mmol) according to GP2 in the dark at 28 °C. The crude product
was purified via column chromatography (isohexane/ ethyl acetate : 10/1)
1-(3-Bromophenyl)-2-phenylpropan-2-ol (5d). a) Compound 5d was
prepared from 3-bromophenyl diazonium tetrafluoroborate (1d, 271 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and water
according to GP1 under blue LED irradiation. The crude product was
purified via column chromatography (isohexane/ ethyl acetate : 6/1) to
give 5d (216 mg, 0.74 mmol, 74%) as a red oil. b) Compound 5d was
prepared from 3-bromophenyl diazonium tetrafluoroborate (1d, 271 mg,
1.00 mmol) and α-methylstyrene (3a, 0.78 mL, 6.00 mmol) according to
GP2 under blue LED irradiation. The crude product was purified via
column chromatography (isohexane/ ethyl acetate : 20/1  10/1) to give
5d (222 mg, 0.76 mmol, 76%) as a red oil. Rf = 0.7 (isohexane/ethyl
acetate = 4:1) [UV]. 1H-NMR (CDCl3, 400 MHz) δ (ppm) = 7.41 – 7.30 (m,
5H), 7.29 – 7.24 (m, 1H), 7.17 (t, J = 1.7 Hz, 1H), 7.07 (t, J = 7.8 Hz, 1H),
6.92 – 6.88 (m, 1H), 3.07 (d, J = 13.3 Hz, 1H), 2.97 (d, J = 13.3 Hz, 1H),
1.69 (bs, 1H), 1.57 (s, 3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 147.3,
139.4, 133.7, 129.8, 129.6, 129.3, 128.3, 127.1, 125.0, 122.2, 74.6, 50.3,
29.4. The analytical data are in agreement with those reported in
literature.[15]
to give 5a (195 mg, 0.79 mmol, 79%) as
a yellow oil. Rf = 0.7
(isohexane/ethyl acetate = 4:1) [UV]. 1H-NMR (CDCl3, 400 MHz) δ (ppm)
= 7.36 – 7.27 (m, 4H), 7.25 – 7.20 (m, 1H), 7.14 (d, J = 8.5 Hz, 2H), 6.87
(d, J = 8.5 Hz, 2H), 3.05 (d, J = 13.4 Hz, 1H), 2.96 (d, J = 13.4 Hz, 1H),
1.91 (bs, 1H), 1.53 (s, 3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 147.2,
135.4, 132.6, 132.0, 128.2, 128.1, 126.9, 125.1, 74.6, 49.9, 29.3. The
analytical data are in agreement with those reported in literature.[15]
1-(3-Fluorophenyl)-2-phenylpropan-2-ol (5e). Compound 5e was
prepared from 3-fluorophenyl diazonium tetrafluoroborate (1e, 210 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and water
according to GP1 under blue LED irradiation. The crude product was
purified via column chromatography (isohexane/ ethyl acetate : 8/1) to
1-(4-Fluorophenyl)-2-phenylpropan-2-ol (5b). a) Compound 5b was
prepared from 4-fluorophenyl diazonium tetrafluoroborate (1b, 210 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and water
according to GP1 under blue LED irradiation. Before workup potassium
acetate (147 mg, 1.50 mmol) was added to the mixture. The crude
product was purified via column chromatography (isohexane/ ethyl
acetate : 20/1  10/1  6/1) to give 5b (188 mg, 0.82 mmol, 82%) as an
orange oil. b) Compound 5b was prepared from 4-fluorophenyl
diazonium tetrafluoroborate (1b, 210 mg, 1.00 mmol) and α-
methylstyrene (3a, 0.78 mL, 6.00 mmol) according to GP2 under blue
LED irradiation. The crude product was purified via column
chromatography (isohexane/ ethyl acetate : 20/1) to give 5b (94 mg, 0.41
mmol, 41%) as an orange oil. Rf = 0.7 (isohexane/ethyl acetate = 4:1)
[UV]. 1H-NMR (CDCl3, 400 MHz) δ (ppm) = 7.39 – 7.29 (m, 4H), 7.28 –
7.22 (m, 1H), 6.95 – 6.85 (m, 4H), 3.09 (d, J = 13.5 Hz, 1H), 2.99 (d, J =
13.5 Hz, 1H), 1.57 (s, 3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 163.2,
160.7, 147.3, 132.1 (d, J = 7.8 Hz), 128.2, 126.9, 125.1, 114.9 (d,
J = 21.1 Hz), 74.6, 49.8, 29.5. The analytical data are in agreement with
those reported in literature.[15]
give 5e (164 mg, 0.71 mmol, 71%) as
a yellow oil. Rf = 0.7
(isohexane/ethyl acetate = 4:1) [UV]. 1H-NMR (CDCl3, 400 MHz) δ (ppm)
= 7.41 – 7.31 (m, 4H), 7.28 – 7.23 (m, 1H), 7.17 (td, J = 7.9, 6.1 Hz, 1H),
6.93 – 6.87 (m, 1H), 6.78 (d, J = 7.6 Hz, 1H), 6.72 – 6.68 (m, 1H), 3.11 (d,
J = 13.3 Hz, 1H), 3.01 (d, J = 13.3 Hz, 1H), 1.58 (s, 3H). DEPTQ (CDCl3,
101 MHz) δ (ppm) = 163.8, 161.4, 147.3, 129.4 (d, J = 8.3 Hz), 128.3,
127.0, 126.4 (d, J = 2.8 Hz), 125.0, 117.6 (d, J = 21.0 Hz), 113.6 (d,
J = 21.0 Hz), 74.6, 50.3 (d, J = 1.6 Hz), 29.5. The analytical data are in
agreement with those reported in literature.[15]
Methyl 4-(2-hydroxy-2-phenylpropyl)benzoate (5f). Compound 5f was
prepared from 4-(methoxycarbonyl)phenyldiazonium tetrafluoroborate (1f,
250 mg, 1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and
water according to GP1 under blue LED irradiation. The crude product
was purified via column chromatography (isohexane/ ethyl acetate : 6/1)
to give 5f (134 mg, 0.50 mmol, 50%) as an orange oil. Rf = 0.4
(isohexane/ethyl acetate = 4:1) [UV]. 1H-NMR (CDCl3, 400 MHz) δ (ppm)
= 7.89 (d, J = 8.4 Hz, 2H), 7.40 – 7.32 (m, 4H), 7.30 – 7.24 (m, 1H), 7.07
(d, J = 8.4 Hz, 2H), 3.91 (s, 3H), 3.19 (d, J = 13.1 Hz, 1H), 3.10 (d, J =
13.1 Hz, 1H), 1.61 (s, 3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 167.2,
147.2, 142.5, 130.8, 129.3, 128.6, 128.3, 127.0, 125.1, 74.7, 52.2, 50.7,
29.6. The analytical data are in agreement with those reported in
literature.[15]
1-(4-Bromophenyl)-2-phenylpropan-2-ol (5c). a) Compound 5c was
prepared from 4-bromophenyl diazonium tetrafluoroborate (1c, 271 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and water
according to GP1 under blue LED irradiation. The crude product was
purified via column chromatography (isohexane/ ethyl acetate : 6/1) to
give 5c (205 mg, 0.70 mmol, 70%) as a red oil. b) Compound 5c was
prepared from 4-bromophenyl diazonium tetrafluoroborate (1c, 271 mg,
1.00 mmol) and α-methylstyrene (3a, 0.78 mL, 6.00 mmol) according to
GP2 under blue LED irradiation. The crude product was purified via
column chromatography (isohexane/ ethyl acetate : 20/1  10/1) to give
5c (244 mg, 0.84 mmol, 84%) as a red oil. Rf = 0.7 (isohexane/ethyl
acetate = 4:1) [UV]. 1H-NMR (CDCl3, 400 MHz) δ (ppm) = 7.38 – 7.29 (m,
6H), 7.27 – 7.22 (m, 1H), 6.84 (d, J = 8.5 Hz, 2H), 3.07 (d, J = 13.4 Hz,
1H), 2.97 (d, J = 13.4 Hz, 1H), 1.68 (bs, 1H), 1.57 (s, 3H). DEPTQ
(CDCl3, 101 MHz) δ (ppm) = 147.1, 135.8, 132.3, 131.1, 128.2, 126.9,
125.0, 120.7, 74.5, 49.9, 29.4. The analytical data are in agreement with
those reported in literature.[15]
3-Methyl-3-phenylisochroman-1-one (5g). a) Compound 5g was
prepared from 2-(methoxycarbonyl)phenyldiazonium tetrafluoroborate
(1g, 250 mg, 1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and
water according to GP1 under blue LED irradiation. The crude product
was purified via column chromatography (isohexane/ ethyl acetate : 6/1)
to give 5g (196 mg, 0.82 mmol, 82%) as a yellow oil. b) Compound 5g
was
prepared
from
2-(methoxycarbonyl)phenyldiazonium
tetrafluoroborate (1g, 250 mg, 1.00 mmol) and α-methylstyrene (3a, 0.78
mL, 6.00 mmol) according to GP2 under blue LED irradiation. The crude
product was purified via column chromatography (isohexane/ ethyl
acetate : 10/1) to give 5g (189 mg, 0.79 mmol, 79%) as a yellow oil. Rf =
0.3 (isohexane/ethyl acetate = 6:1) [UV]. 1H-NMR (CDCl3, 400 MHz) δ
(ppm) = 8.04 (ddd, J = 7.8, 1.4, 0.6 Hz, 1H), 7.54 – 7.40 (m, 3H), 7.34 –
7
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7.28 (m, 3H), 7.26 – 7.19 (m, 2H), 3.55 (d, J = 16.3 Hz, 1H), 3.43 (d, J =
16.2 Hz, 1H), 1.78 (s, 3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 165.4,
143.7, 138.0, 134.0, 130.1, 128.6, 127.7, 127.6, 127.5, 125.3, 124.8,
83.7, 39.2, 30.3. The analytical data are in agreement with those
reported in literature.[15]
13.4 Hz, 1H), 3.13 (d, J = 13.4 Hz, 1H), 2.26 (bs, 1H), 1.70 (s,
3H).DEPTQ (CDCl3, 101 MHz) δ (ppm) = 144.6, 135.3, 133.2, 132.6,
132.4, 132.0, 128.3, 128.2, 128.0, 127.6, 126.2, 126.0, 123.8, 123.6,
74.8, 49.6, 29.6.The analytical data are in agreement with those reported
in literature.[15]
2-(4-Chlorophenyl)-1,1-diphenylethan-1-ol (5i). Compound 5i was
prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a, 226 mg,
1.00 mmol), 1,1-diphenyl ethylene (3b, 1.06 mL, 6.00 mmol) and water
according to GP1 under blue LED irradiation. The crude product was
purified via column chromatography (100% isohexane  isohexane/
ethyl acetate : 100/1  30/1) to give 5i (76 mg, 0.25 mmol, 25%) as a
light orange oil. Compound 5i was prepared from 4-chlorophenyl
diazonium tetrafluoroborate (1a, 226 mg, 1.00 mmol), 1,1-diphenyl
ethylene (3b, 1.06 mL, 6.00 mmol) and water according to GP2 under
blue LED irradiation. The crude product was purified via column
chromatography (100% isohexane  isohexane/ ethyl acetate : 100/1 
30/1) to give 5i (196 mg, 0.63 mmol, 63%) as a light orange oil. Rf = 0.3
(isohexane/ethyl acetate = 10:1) [UV]. 1H-NMR (CDCl3, 400 MHz) δ
(ppm) = 7.46 – 7.40 (m, 4H), 7.37 – 7.31 (m, 4H), 7.32 – 7.23 (m, 4H),
7.14 (d, J = 8.4 Hz, 2H), 6.84 (d, J = 8.4 Hz, 2H), 3.62 (s, 2H), 2.30 (bs,
1H). DEPTQ (CDCl3, 151 MHz) δ (ppm) = 146.4, 134.6, 132.7, 132.3,
128.2, 128.1, 127.2, 126.3, 78.1, 47.4.The analytical data are in
agreement with those reported in literature.[15]
2-(4-Chlorophenyl)-1-phenylethan-1-ol (5n). Compound 5n was prepared
from 4-chlorophenyl diazonium tetrafluoroborate (1a, 226 mg, 1.00 mmol),
styrene (3g, 0.92 mL, 6.00 mmol) and water according to GP2 under blue
LED irradiation. The yield was determined by 1H NMR spectroscopy
using 1,4-dimethoxybenzene (69 mg, 0.5 mmol) yielding in 15% of
compound 5n. The analytical data is in agreement with those reported in
literature.[35]
2-(4-Chlorophenyl)-1-(4-methoxyphenyl)ethan-1-ol (5o). Compound 5o
was prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a,
226 mg, 1.00 mmol), 1-methoxy-4-vinylbenzene (3h, 0.80 mL,
6.00 mmol) and water according to GP2 under blue LED irradiation. The
crude product was purified via column chromatography (isohexane/ ethyl
acetate : 6/1  4/1) to give 5o (120 mg, 0.46 mmol, 46%) as an orange
oil. Rf = 0.5 (isohexane/ethyl acetate = 2:1) [UV]. 1H-NMR (CDCl3,
400 MHz) δ (ppm) = 7.30 – 7.21 (m, 4H), 7.10 (d, J = 8.5 Hz, 2H), 6.89 (d,
J = 8.7 Hz, 2H), 4.82 (dd, J = 7.7, 5.6 Hz, 1H), 3.83 (s, 3H), 3.07 – 2.93
(m, 2H), 2.05 (bs, 1H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 159.2, 136.7,
135.8, 132.33, 131.0, 128.5, 127.3, 113.9, 75.0, 55.4, 45.4. The
analytical data are in agreement with those reported in literature.[15]
1,2-Bis(4-chlorophenyl)propan-2-ol (5j). Compound 5j was prepared from
4-chlorophenyl diazonium tetrafluoroborate (1a, 180 mg, 0.78 mmol), 1-
chloro-4-(prop-1-en-2-yl)benzene (3c, 711 mg, 4.66 mmol) and water
according to GP2 under blue LED irradiation. The crude product was
purified via column chromatography (100% isohexane  isohexane/
ethyl acetate : 10/1) to give 5j (144 mg, 0.51 mmol, 66%) as an orange
oil. Rf = 0.3 (isohexane/ethyl acetate = 10:1) [UV]. 1H-NMR (CDCl3,
400 MHz) δ (ppm) = 7.28 (s, 4H), 7.18 (d, J = 8.4 Hz, 2H), 6.89 (d, J =
8.4 Hz, 2H), 3.03 (d, J = 13.4 Hz, 1H), 2.96 (d, J = 13.4 Hz, 1H), 1.54 (s,
3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 145.7, 135.0, 132.7, 132.6,
131.9, 128.2, 128.2, 126.6, 74.3, 49.8, 29.4.The analytical data are in
agreement with those reported in literature.[15]
1-Chloro-4-(2-methoxy-2-phenylpropyl)benzene (8a). Compound 8a was
prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a, 226 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and methanol
according to GP2 under blue LED irradiation. The crude product was
purified via column chromatography (100% isohexane  isohexane/
ethyl acetate : 2/1) to give 8a (194 mg, 0.74 mmol, 74%) as a yellow oil.
Rf
= 0.4 (isohexane/ethyl acetate =
10:1) [UV]. 1H-NMR (CDCl3,
400 MHz) δ (ppm) = 7.34 – 7.22 (m, 5H), 7.11 (d, J = 8.5 Hz, 2H), 6.78 (d,
J = 8.6 Hz, 2H), 3.10 (s, 3H), 2.98 (d, J = 13.2 Hz, 1H), 2.92 (d, J = 13.3
Hz, 1H), 1.48 (s, 3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 144.0, 136.0,
132.1, 128.2, 127.7, 127.2, 126.8, 79.7, 50.7, 50.3, 21.3. The analytical
data are in agreement with those reported in literature.[15]
1-(4-Chlorophenyl)-2-(4-methoxyphenyl)propan-2-ol (5k). Compound 5k
was prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a,
199 mg, 0.86 mmol), 1-methoxy-4-(prop-1-en-2-yl)benzene (3d, 760 mg,
5.13 mmol) and water according to GP2 under blue LED irradiation. The
crude product was purified via column chromatography (100% isohexane
 isohexane/ ethyl acetate : 5/1) to give 5k (199 mg, 0.72 mmol, 84%)
as an orange oil. Rf = 0.2 (isohexane/ethyl acetate = 5:1) [UV]. 1H-NMR
(CDCl3, 400 MHz) δ (ppm) = 7.27 (d, J = 8.9 Hz, 2H), 7.17 (d, J = 8.4 Hz,
2H), 6.89 (d, J = 8.7 Hz, 2H), 6.85 (d, J = 8.9 Hz, 2H), 3.81 (s, 3H), 3.05
(d, J = 13.3 Hz, 1H), 2.97 (d, J = 13.3 Hz, 1H), 1.54 (s, 3H). DEPTQ
(CDCl3, 101 MHz) δ (ppm) =158.5, 139.4, 135.6, 132.6, 132.0, 128.2,
126.3, 113.5, 74.4, 55.4, 50.1, 29.5.The analytical data are in agreement
with those reported in literature.[15]
1-Fluoro-4-(2-methoxy-2-phenylpropyl)benzene (8b). Compound 8b was
prepared from 4-fluorophenyl diazonium tetrafluoroborate (1b, 210 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and methanol
according to GP2 under blue LED irradiation. The crude product was
purified via column chromatography (100% isohexane  isohexane/
ethyl acetate : 20/1) to give 8b (91 mg, 0.37 mmol, 37%) as a yellow oil.
Rf
= 0.6 (isohexane/ethyl acetate =
20:1) [UV]. 1H-NMR (CDCl3,
400 MHz) δ (ppm) = 7.34 – 7.20 (m, 5H), 6.94 – 6.59 (m, 4H), 3.10 (s,
3H), 2.98 (d, J = 13.3 Hz, 1H), 2.93 (d, J = 13.3 Hz, 1H), 1.49 (s, 3H).
DEPTQ (CDCl3, 101 MHz) δ (ppm) = 162.4, 160.8, 144.0, 133.1 (d, J =
3.2 Hz), 132.1 (d, J = 7.7 Hz), 128.0, 127.0, 126.7, 114.3 (d, J = 20.7 Hz),
79.6, 50.5, 45.0, 21.2. HRMS (ESI): calculated for C15H14F [M-
CH3OH+H+]: 213.1074, found: 213.1075.
1-(4-Chlorophenyl)-2-(naphthalen-2-yl)propan-2-ol (5m). Compound 5m
was prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a,
226 mg, 1.00 mmol), 2-(prop-1-en-2-yl)naphthalene (3f, 1009 mg,
6.00 mmol) and water according to GP2 under blue LED irradiation. The
crude product was purified via column chromatography (isohexane/ ethyl
acetate : 6/1) to give 5m (238 mg, 0.80 mmol, 80%) as a yellow oil. Rf =
0.3 (isohexane/ethyl acetate = 4:1) [UV]. 1H-NMR (CDCl3, 400 MHz) δ
(ppm) = 7.98 – 7.80 (m, 4H), 7.59 (dd, J = 8.6, 2.0 Hz, 1H), 7.58 – 7.52
(m, 2H), 7.20 (d, J = 8.4 Hz, 2H), 6.96 (d, J = 8.4 Hz, 2H), 3.23 (d, J =
1-Bromo-4-(2-methoxy-2-phenylpropyl)benzene (8c). Compound 8c was
prepared from 4-bromophenyl diazonium tetrafluoroborate (1c, 271 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and methanol
according to GP2 under blue LED irradiation. The crude product was
purified via column chromatography (100% isohexane  isohexane/
ethyl acetate : 100/1  50/1) to give 8c (208 mg, 0.68 mmol, 68%) as an
orange oil. Rf = 0.4 (isohexane/ethyl acetate = 50:1) [UV]. 1H-NMR
8
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10.1002/chem.202004234
Chemistry - A European Journal
FULL PAPER
(CDCl3, 400 MHz) δ (ppm) = 7.40 – 7.22 (m, 7H), 6.77 (d, J = 8.7 Hz,
2H), 3.13 (s, 3H), 3.00 (d, J = 13.2 Hz, 1H), 2.94 (d, J = 13.2 Hz, 1H),
1.52 (s, 3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 143.9, 136.5, 132.5,
130.6, 128.2, 127.2, 126.7, 120.3, 79.6, 50.6, 50.3, 21.3. HRMS (ESI):
calculated for C15H14Br [M-CH3OH+H+]: 273.0273, found: 273.0272.
(t, J = 7.3 Hz, 3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 144.9, 136.3,
132.2, 132.0, 128.1, 127.6, 127.1, 126.7, 79.0, 62.2, 50.8, 32.6, 21.8,
19.6, 14.2. HRMS (ESI): calculated for C15H14Cl [M-C4H10O+H+]:
229.0779, found: 229.0782.
1-Chloro-4-(2-(pentyloxy)-2-phenylpropyl)benzene (8h). Compound 8h
was prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a, 226
mg, 1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and pentanol
according to GP2 under blue LED irradiation. The crude product was
purified via column chromatography (100% isohexane  isohexane/
ethyl acetate : 100/1) to give 8h (172 mg, 0.54 mmol, 54%) as an orange
oil. Rf = 0.3 (isohexane/ethyl acetate = 100:1) [UV]. 1H-NMR (CDCl3,
400 MHz) δ (ppm) = 7.33 – 7.21 (m, 5H), 7.11 (d, J = 8.5 Hz, 2H), 6.82 (d,
J = 8.5 Hz, 2H), 3.25 (dt, J = 8.7, 6.7 Hz, 1H), 3.06 (dt, J = 8.7, 6.7 Hz,
1H), 2.97 (d, J = 13.2 Hz, 1H), 2.88 (d, J = 13.2 Hz, 1H), 1.59 – 1.51 (m,
2H), 1.48 (s, 3H), 1.29 (tdd, J = 11.0, 6.0, 3.6 Hz, 4H), 0.89 (t, J = 7.1 Hz,
3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 145.0, 136.3, 132.2, 132.1,
128.1, 127.7, 127.1, 126.7, 79.0, 62.6, 50.8, 30.2, 28.6, 22.7, 21.9, 14.2.
HRMS (ESI): calculated for C15H14Cl [M-C5H12O+H+]: 229.0779, found:
229.0781.
1-Bromo-3-(2-methoxy-2-phenylpropyl)benzene (8d). Compound 8d was
prepared from 3-bromophenyl diazonium tetrafluoroborate (1d, 271 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and methanol
according to GP2 under blue LED irradiation. The crude product purified
via column chromatography (100% isohexane
 isohexane/ ethyl
acetate : 100/1) to give 8d (278 mg, 0.91 mmol, 91%) as a brown oil. Rf =
1
0.4 (isohexane/ethyl acetate = 100:1) [UV]. H-NMR (CDCl3, 400 MHz) δ
(ppm) = 7.36 – 7.22 (m, 5H), 7.04 (t, J = 1.9 Hz, 1H), 7.01 (t, J = 7.8 Hz,
1H), 6.78 (d, J = 7.7 Hz, 1H), 3.10 (s, 3H), 2.98 (d, J = 13.3 Hz, 1H), 2.90
(d, J = 13.3 Hz, 1H), 1.50 (s, 3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) =
143.9, 139.9, 133.7, 129.3, 129.2, 129.0, 128.1, 127.1, 126.6, 121.6,
79.5, 50.5, 50.5, 21.2. HRMS (ESI): calculated for C15H14Br
[M-CH3OH+H+]: 273.0273, found: 273.0272.
1-Chloro-4-(2-ethoxy-2-phenylpropyl)benzene (8e). Compound 8e was
prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a, 226 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and ethanol
according to GP2 under blue LED irradiation. The crude product was
purified via column chromatography (100% isohexane  isohexane/
ethyl acetate : 200/1  100/1  20/1) to give 8e (190 mg, 0.69 mmol,
69%) as an orange oil. Rf = 0.8 (isohexane/ethyl acetate = 10:1) [UV]. 1H-
NMR (CDCl3, 400 MHz) δ (ppm) = 7.33 – 7.22 (m, 5H), 7.10 (d, J = 8.5
Hz, 2H), 6.79 (d, J = 8.5 Hz, 2H), 3.35 (dq, J = 8.8, 6.9 Hz, 1H), 3.13 (dq,
J = 8.8, 7.0 Hz, 1H), 2.98 (d, J = 13.2 Hz, 1H), 2.90 (d, J = 13.2 Hz, 1H),
1.48 (s, 3H), 1.17 (t, J = 7.0 Hz, 3H). DEPTQ (CDCl3, 101 MHz) δ (ppm)
= 144.8, 136.2, 132.2, 132.1, 128.1, 127.7, 127.1, 126.6, 79.3, 58.0, 50.6,
21.9, 15.9. HRMS (ESI): calculated for C17H19ClNaO [M+Na]: 297.1017,
found: 297.1021.
1-Chloro-4-(2-(octyloxy)-2-phenylpropyl)benzene (8i). Compound 8i was
prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a, 226 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and octanol
according to GP2 under blue LED irradiation. The crude product was
purified via column chromatography (100% isohexane  isohexane/
ethyl acetate : 100/1) to give 8i (220 mg, 0.61 mmol, 61%) as an orange
oil. Rf = 0.3 (isohexane/ethyl acetate = 100:1) [UV]. 1H-NMR (CDCl3,
400 MHz) δ (ppm) = 7.33 – 7.21 (m, 5H), 7.11 (d, J = 8.5 Hz, 2H), 6.82 (d,
J = 8.5 Hz, 2H), 3.25 (dt, J = 8.7, 6.7 Hz, 1H), 3.06 (dt, J = 8.7, 6.7 Hz,
1H), 2.97 (d, J = 13.2 Hz, 1H), 2.88 (d, J = 13.2 Hz, 1H), 1.59 – 1.51 (m,
2H), 1.48 (s, 3H), 1.29 (tdd, J = 11.0, 6.0, 3.6 Hz, 4H), 0.89 (t, J = 7.1 Hz,
3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 144.8, 136.2, 132.1, 132.0,
128.0, 127.5, 127.0, 126.5, 78.9, 62.4, 50.7, 31.9, 30.4, 29.5, 29.4, 26.3,
22.7, 21.7, 14.2. HRMS (ESI): calculated for C15H14Cl [M-C8H18O+H+]:
229.0779, found: 229.0781.
1-Chloro-4-(2-phenyl-2-propoxypropyl)benzene (8f). Compound 8f was
prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a, 226 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and propanol
according to GP2 under blue LED irradiation. The crude product was
purified via column chromatography (100% isohexane  isohexane/
ethyl acetate : 100/1) to give 8f (196 mg, 0.68 mmol, 68%) as a yellow oil.
Rf = 0.4 (isohexane/ethyl acetate = 100:1) [UV]. 1H-NMR (CDCl3,
400 MHz) δ (ppm) = 7.36 – 7.21 (m, 5H), 7.12 (d, J = 8.4 Hz, 2H), 6.84 (d,
J = 8.5 Hz, 2H), 3.23 (dt, J = 8.7, 6.7 Hz, 1H), 3.05 (dt, J = 8.7, 6.7 Hz,
1H), 2.99 (d, J = 13.2 Hz, 1H), 2.90 (d, J = 13.2 Hz, 1H), 1.59 (dtd, J =
14.1, 7.4, 6.6 Hz, 2H), 1.50 (s, 3H), 0.92 (t, J = 7.4 Hz, 3H).DEPTQ
(CDCl3, 101 MHz) δ (ppm) = 144.9, 136.3, 132.2, 132.0, 128.1, 127.6,
127.1, 126.6, 78.9, 64.2, 50.8, 23.7, 21.8, 11.0. HRMS (ESI): calculated
for C15H14Cl [M-C3H8O+H+]: 229.0779, found: 229.0781.
1-(2-(Allyloxy)-2-phenylpropyl)-4-chlorobenzene (8j). Compound 8j was
prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a, 226 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and allyl alcohol
according to GP2 under blue LED irradiation. The crude product was
purified via column chromatography (100% isohexane  isohexane/
ethyl acetate : 100/1) to give 8j (132 mg, 0.46 mmol, 46%) as a red oil. Rf
1
= 0.3 (isohexane/ethyl acetate = 100:1) [UV]. H-NMR (CDCl3, 400 MHz)
δ (ppm) = 7.38 – 7.24 (m, 5H), 7.13 (d, J = 8.4 Hz, 2H), 6.83 (d, J = 8.4
Hz, 2H), 5.93 (ddt, J = 17.2, 10.5, 5.0 Hz, 1H), 5.34 (dd, J = 17.2, 1.9 Hz,
1H), 5.16 (dd, J = 10.4, 1.8 Hz, 1H), 3.86 (ddt, J = 12.9, 5.2, 1.6 Hz, 1H),
3.69 (ddt, J = 12.8, 4.8, 1.7 Hz, 1H), 3.07 – 2.92 (m, 2H), 1.55 (s, 3H).
DEPTQ (CDCl3, 101 MHz) δ (ppm) = 144.3, 136.0, 135.6, 132.2, 132.1,
128.2, 127.7, 127.3, 126.6, 115.5, 79.8, 63.9, 50.7, 22.0. HRMS (ESI):
calculated for C15H14Cl [M-C3H6O+H+]: 229.0779, found: 229.0781.
1-(2-Butoxy-2-phenylpropyl)-4-chlorobenzene (8g). Compound 8g was
prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a, 226 mg,
1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and butanol
according to GP2 under blue LED irradiation. The crude product was
purified via column chromatography (100% isohexane  isohexane/
ethyl acetate : 100/1) to give 8g (209 mg, 0.69 mmol, 69%) as an orange
oil. Rf = 0.3 (isohexane/ethyl acetate = 100:1) [UV]. 1H-NMR (CDCl3,
400 MHz) δ (ppm) = 7.33 – 7.22 (m, 5H), 7.11 (d, J = 8.5 Hz, 2H), 6.83 (d,
J = 8.5 Hz, 2H), 3.26 (dt, J = 8.8, 6.6 Hz, 1H), 3.08 (dt, J = 8.8, 6.6 Hz,
1H), 2.98 (d, J = 13.2 Hz, 1H), 2.89 (d, J = 13.2 Hz, 1H), 1.55 (ddt, J =
12.1, 8.8, 4.0 Hz, 2H), 1.48 (s, 3H), 1.37 (dq, J = 14.4, 7.3 Hz, 2H), 0.90
1-(2-(Benzyloxy)-2-phenylpropyl)-4-chlorobenzene (8k). Compound 8k
was prepared from 4-chlorophenyl diazonium tetrafluoroborate (1a, 226
mg, 1.00 mmol), α-methylstyrene (3a, 0.78 mL, 6.00 mmol) and benzyl
alcohol according to GP2 under blue LED irradiation. The crude product
was purified via column chromatography (100% isohexane  isohexane/
ethyl acetate : 100/1  50/1) to give 8k (227 mg, 0.67 mmol, 67%) as a
1
yellow oil. Rf = 0.2 (isohexane 100%) [UV]. H-NMR (CDCl3, 400 MHz) δ
(ppm) = 7.44 – 7.31 (m, 10H), 7.18 (d, J = 8.5 Hz, 2H), 6.92 (d, J = 8.5
Hz, 2H), 4.43 (d, J = 11.5 Hz, 1H), 4.26 (d, J = 11.5 Hz, 1H), 3.14 (d, J =
13.3 Hz, 1H), 3.05 (d, J = 13.3 Hz, 1H), 1.67 (s, 3H). ). DEPTQ (CDCl3,
9
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10.1002/chem.202004234
Chemistry - A European Journal
FULL PAPER
101 MHz) δ (ppm) = 144.3, 139.4, 136.0, 132.2, 132.1, 128.4, 128.2,
127.7, 127.3, 127.2, 127.2, 126.6, 79.8, 64.8, 50.8, 21.9. HRMS (ESI):
calculated for C15H14Cl [M-C7H8O+H+]: 229.0779, found: 229.0779.
1H), 2.87 (dd, J = 13.2, 5.3 Hz, 1H), 1.97 (dt, J = 14.6, 7.8 Hz, 2H), 1.68
(d, J = 1.3 Hz, 2H), 1.60 (dd, J = 6.5, 1.3 Hz, 3H), 1.56 (s, 3H), 1.50 –
1.46 (m, 3H), 1.42 – 1.20 (m, 2H), 1.18 – 1.07 (m, 1H), 0.87 – 0.80 (m,
3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 144.9 (d), 136.3, 132.2, 132.0,
128.1, 127.6, 127.1, 126.6 (d), 125.0, 79.0, 60.8, 60.7, 50.8 (d), 37.6,
37.5, 37.4, 37.3, 29.9, 29.7 (d), 25.9 (d), 25.7, 25.6, 21.8, 19.9, 19.7, 17.8
(d). HRMS (ESI): calculated for C15H14Cl [M-C10H20O +H+]: 229.0779,
found: 229.0777.
1-Chloro-4-(2-(cyclohexylmethoxy)-2-phenylpropyl)benzene
(8l).
Compound 8l was prepared from 4-chlorophenyl diazonium
tetrafluoroborate (1a, 226 mg, 1.00 mmol), α-methylstyrene (3a, 0.78 mL,
6.00 mmol) and cyclohexylmethanol according to GP2 under blue LED
irradiation. The crude product was purified via column chromatography
(100% isohexane  isohexane/ ethyl acetate : 50/1) to give 8l (177 mg,
0.52 mmol, 52%) as a light orange oil. Rf = 0.4 (isohexane/ethyl acetate =
100:1) [UV]. 1H-NMR (CDCl3, 400 MHz) δ (ppm) = 7.36 – 7.25 (m, 5H),
7.16 (d, J = 8.5 Hz, 2H), 6.89 (d, J = 8.5 Hz, 2H), 3.10 (dd, J = 8.6,
6.4 Hz, 1H), 3.02 (d, J = 13.2 Hz, 1H), 2.96 – 2.88 (m, 2H), 1.87 –
1.69 (m, 5H), 1.66 – 1.54 (m, 1H), 1.51 (s, 3H), 1.37 – 1.16 (m, 3H), 1.03
– 0.90 (m, 2H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 144.9, 136.3, 132.3,
132.0, 128.0, 127.6, 127.0, 126.7, 78.6, 68.1, 50.8, 38.7, 30.5, 26.9, 26.2,
21.8. HRMS (ESI): calculated for C15H14Cl [M-C7H14O+H+]: 229.0779,
found: 229.0781.
1-Chloro-4-(2-((3,7-dimethylocta-2,6-dien-1-yl)oxy)-2-
phenylpropyl)benzene (8q). Compound 8q was prepared from 4-
chlorophenyl diazonium tetrafluoroborate (1a, 226 mg, 1.00 mmol), α-
methylstyrene (3a, 0.78 mL, 6.00 mmol) and geraniol according to GP2
under blue LED irradiation. The crude product was purified via column
chromatography (isohexane/ dichloromethane : 6/1) to give 8q (139 mg,
0.36 mmol, 36%) as an orange oil. Rf = 0.2 (isohexane/dichloromethane
= 5:1) [UV]. 1H-NMR (CDCl3, 400 MHz) δ (ppm) = 7.38 – 7.25 (m, 5H),
7.12 (d, J = 8.4 Hz, 2H), 6.80 (d, J = 8.4 Hz, 2H), 5.39 (ddd, J = 6.6, 5.9,
1.3 Hz, 1H), 5.14 (ddt, J = 7.0, 5.5, 1.4 Hz, 1H), 3.88 (ddd, J = 11.2, 6.6,
0.8 Hz, 1H), 3.67 (ddd, J = 11.2, 6.5, 0.9 Hz, 1H), 3.04 (d, J = 13.2 Hz,
1H), 2.97 (d, J = 13.2 Hz, 1H), 2.17 – 2.03 (m, 4H), 1.72 (d, J = 1.3 Hz,
3H), 1.65 (d, J = 1.3 Hz, 3H), 1.57 (d, J = 1.3 Hz, 3H), 1.54 (s, 3H). ).
DEPTQ (CDCl3, 101 MHz) δ (ppm) = 144.4, 138.7, 136.0, 132.1, 132.0,
131.6, 128.0, 127.6, 127.1, 126.7, 124.1, 121.6, 79.5, 59.8, 50.5, 39.7,
26.4, 25.8, 21.7, 17.8, 16.5. HRMS (ESI): calculated for C15H14Cl [M-
C10H18O +H+]: 229.0779, found: 229.0777.
2-((1-(4-Chlorophenyl)-2-phenylpropan-2-yl)oxy)ethan-1-ol
(8m).
Compound 8m was prepared from 4-chlorophenyl diazonium
tetrafluoroborate (1a, 226 mg, 1.00 mmol), α-methylstyrene (3a, 0.78 mL,
6.00 mmol) and ethylene glycol according to GP2 under blue LED
irradiation. The crude product was purified via column chromatography
(100% isohexane  isohexane/ ethyl acetate : 4/1) to give 8m (138 mg,
0.47 mmol, 47%) as an orange oil. Rf = 0.3 (isohexane/ethyl acetate =
4:1) [UV]. 1H-NMR (CDCl3, 400 MHz) δ (ppm) = 7.34 – 7.23 (m, 5H), 7.12
(d, J = 8.4 Hz, 2H), 6.81 (d, J = 8.5 Hz, 2H), 3.77 – 3.66 (m, 2H), 3.39
(ddd, J = 9.8, 6.3, 3.5 Hz, 1H), 3.24 (ddd, J = 9.6, 5.4, 3.5 Hz, 1H), 3.02
(d, J = 13.3 Hz, 1H), 2.94 (d, J = 13.3 Hz, 1H), 1.88 (bs, 1H), 1.52 (s, 3H).
DEPTQ (CDCl3, 101 MHz) δ (ppm) = 143.9, 135.8, 132.2, 132.0, 128.2,
127.7, 127.3, 126.5, 79.2, 63.4, 62.4, 50.5, 21.8. HRMS (ESI): calculated
for C15H14Cl [M-C2H6O2+H+]: 229.0779, found: 229.0780.
(2-Methoxypropan-2-yl)benzene (9). Compound 9 was prepared from 4-
chlorophenyl diazonium tetrafluoroborate (1a, 226 mg, 1.00 mmol), α-
methylstyrene (3a, 0.78 mL, 6.00 mmol) and methanol according to GP1
under blue LED irradiation. The crude product was purified via column
chromatography (100% isohexane  isohexane/ ethyl acetate : 10/1).
1H-NMR (CDCl3, 400 MHz) δ (ppm) = 7.44-7.20 (m, 5H), 3.07 (s, 3H),
1.54 (s, 6H). The analytical data are in agreement with those reported in
literature.[36]
1-(2-(4-(Benzyloxy)butoxy)-2-phenylpropyl)-4-chlorobenzene
(8n).
Compound 8n was prepared from 4-chlorophenyl diazonium
tetrafluoroborate (1a, 226 mg, 1.00 mmol), α-methylstyrene (3a, 0.78 mL,
6.00 mmol) and 4-benzyloxy-1-butanol according to GP2 under blue LED
irradiation. The crude product was purified via column chromatography
(100% isohexane  isohexane/ ethyl acetate : 50/1  25/1) to give 8n
(197 mg, 0.48 mmol, 48%) as an orange oil. Rf = 0.3 (isohexane/ethyl
acetate = 50:1) [UV]. 1H-NMR (CDCl3, 400 MHz) δ (ppm) = 7.39 – 7.24
(m, 10H), 7.13 (d, J = 8.5 Hz, 2H), 6.84 (d, J = 8.5 Hz, 2H), 4.52 (s, 2H),
3.50 (t, J = 6.3 Hz, 2H), 3.29 (dt, J = 8.7, 6.3 Hz, 1H), 3.12 (dt, J = 8.7,
6.2 Hz, 1H), 2.99 (d, J = 13.2 Hz, 1H), 2.89 (d, J = 13.2 Hz, 1H), 1.77 –
1.62 (m, 4H), 1.49 (s, 3H). DEPTQ (CDCl3, 101 MHz) δ (ppm) = 144.8,
138.7, 136.2, 132.2, 132.0, 128.5, 128.1, 127.7, 127.6 (x2), 127.1, 126.6,
79.0, 72.97, 70.4, 62.2, 50.7, 27.1, 26.8, 21.8. HRMS (ESI): calculated
for C15H14Cl [M-C11H16O2+H+]: 229.0779, found: 229.0781; calculated for
C11H17O2 [M-C15H13Cl+H+]: 181.1223, found: 181.1224.
Acknowledgements
The authors would like to thank Elisabeth Eckenberger for
technical assistance. L.-M.A. is also grateful for support by the
Graduate School Molecular Science (GSMS). The DPV
measurements supported by Pascal Gazetas and Prof. Dr.
Norbert Jux, (FAU Erlangen-Nürnberg) are gratefully
acknowledged.
Keywords: Meerwein • Arylation • Diazonium • Styrene •
Biomimetic
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10.1002/chem.202004234
Chemistry - A European Journal
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As shown in this work, Meerwein-type carbooxygenations can
be conducted under fully biocompatible conditions, including
ambient temperature and the absence of catalysts or unnatural
additives. Surprisingly, the reactions can be further promoted by
visible light irradiation, although the reaction mixtures show only
very weak absorptions in the respective wavelength range.
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10.1002/chem.202004234
Chemistry - A European Journal
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