Electrochemical functionalization of 1,3-diisopropylbenzene

Article abstract of DOI:10.1002/cssc.201000046

The anodic oxidation of 1,3-diisopropylbenzene in methanol gave exclusively the desired dimethoxy-functionalized product in excellent yield when potassium bromate was utilized as supporting electrolyte. Similar electrochemical conversions in other alcoholic solvents were not successful based on the low conductivity of the mixture. The introduction of other alcohols could then be realized when the dimethoxy derivative was converted under S_N1 conditions in alcohols used as solvent. Thereby, higher alcohols could be introduced in moderate yields and acceptable selectivities.

Full text of DOI:10.1002/cssc.201000046

DOI: 10.1002/cssc.201000046
Electrochemical Functionalization of 1,3-Diisopropyl-
benzene
Martin A. Bohn,[a] Gerhard Hilt,*[a] Patrick Bolze,[a] and Christoph Gꢀrtler*[b]
Dedicated to the memory of Prof. Dr. Eberhard Steckhan
The anodic oxidation of 1,3-diisopropylbenzene in methanol
gave exclusively the desired dimethoxy-functionalized product
in excellent yield when potassium bromate was utilized as sup-
porting electrolyte. Similar electrochemical conversions in
other alcoholic solvents were not successful based on the low
conductivity of the mixture. The introduction of other alcohols
could then be realized when the dimethoxy derivative was
converted under SN1 conditions in alcohols used as solvent.
Thereby, higher alcohols could be introduced in moderate
yields and acceptable selectivities.
Introduction
Electrochemical transformations are considered to be proto-
type reactions in terms of sustainable chemistry.[1] Anodic oxi-
dations of the side chain of aromatic hydrocarbons in benzylic
position (alkoxylations)[2] are a desirable alternative to radical
type functionalization of the benzylic position by chlorine or
bromine. In addition, the introduction of the desired nucleo-
phile into the functionalized molecule by nucleophilic substitu-
tion generates stoichiometric amounts of side products (in
general metal halides). Therefore, direct functionalization of hy-
drocarbons at the benzylic positions, which avoids side prod-
ucts utilizing the anode as mass-free oxidant, is a sustainable
alternative of considerable interest not only for academics but
also for industrial chemists.
vestigation upon the simplest possible electrochemical setup.
One of the main goals was the determination of simple and
straightforward preparative procedures leading to the desired
products.
Formamide presents several advantages in this regard: the
polar nature of the solvent greatly aids the dissolution of the
supporting electrolytes and it was postulated that the ob-
tained bis-amide 2 could itself be oxidized, leading to bis-iso-
cyanate 3 (Scheme 2). This compound promises an exciting
range of follow-up chemistry.
1,3-Diisopropylbenzene (DIPB, 1) was selected as starting
material because the functionalization generates a very inter-
esting monomeric building block for the synthesis of oligo-
mers and polymers.[3] The anodic oxidation of 1 in the pres-
ence of suitable nucleophiles (Scheme 1) was envisaged as an
excellent example for sustainable organic electrochemistry.[4]
Scheme 2. Electrochemical functionalization of 1 with formamide.
It became quickly apparent that formamide could not deliv-
er the desired reactivity (Table 1). The electrolysis reactions
proved to be frustratingly unresponsive, leading invariably to
no change in the starting material despite variation of the elec-
Scheme 1. Electrochemical functionalization of 1.
Results and Discussion
Anodic oxidations in nitrogen-containing solvents
[a] M. A. Bohn, Prof. Dr. G. Hilt, Dr. P. Bolze
Fachbereich Chemie, Philipps-Universitꢀt Marburg
Hans-Meerwein-Straße, 35043 Marburg (Germany)
Fax: (+49)6421 2825677
Nitrogen nucleophiles were determined to be of the greatest
interest, as the generated products would be substituted
benzyl amines. To simplify the system as much as possible, it
was decided to utilize formamide as the solvent as well as the
nitrogen source for preliminary studies of the anodic oxidation
and subsequent reactions of the DIPB-based cations. To mini-
mize the requirements for the apparatus, we focused our in-
E-mail: Hilt@chemie.uni-marburg.de
[b] Dr. C. Gꢁrtler
Bayer MaterialScience AG, Geb. B211
51368 Leverkusen (Germany)
E-mail: christoph.guertler@bayerbms.com
ChemSusChem 2010, 3, 823 – 828
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G. Hilt, C. Gꢁrtler et al.
Anodic oxidations in oxygen-containing solvents
Table 1. Screened electrolysis conditions in formamide.
Entry Cathode/ Supporting Current densi- Additive
Conversion[a,b]
After the initial disappointment with nitrogen-based nucleo-
philes, oxygen-based systems were examined next. The first at-
tempt was made with acetic acid as solvent and sodium ace-
tate as the supporting electrolyte.
anode
electrolyte ty [mAcmÀ1
]
1
Camorph
/
LiCl
50
–
–
Camorph
2
3
C
PtWire
amorph/Pt NaCl
50
50
–
–
–
–
Upon GC–MS analysis, an immediate improvement became
apparent. The three major components could be identified as
mono- and bis-acetoxylated compounds 4 and 5, and olefin 6
in a ratio of approximately 1:1:1 by GC–GCMS (Scheme 3). Sev-
/
NaCl
Camorph
Pt/Fe
Pt/Pt
Pt/Pt
Pt/Pt
Pt/Pt
Pt/Pt
Pt/Pt
Pt/Pt
Pt/Pt
Pt/Pt
Pt/Pt
4
5
6
7
8
9
10
11
12
13
14
LiClO4
NaCl
NaBr
100
50
–
–
–
–
–
–
–
–
–
–
–
–
100
500
100
100
100
100
100
100
LiClO4
LiClO4
LiClO4
LiClO4
LiClO4
LiClO4
LiClO4
LiClO4
FeCl3
CuSO4
CoCl2
FeBr2(dppe)
CoBr2(dppe) –
Mn(OAc)3
–
–
[a] Reaction conditions: 1,3-diisopropylbenzene (0.2 mL, 1.05 mmol), sup-
porting electrolyte (300 mg), additive (50 mg), formamide (15 mL), 3 h.
[b] Conversion determined by GC–MS analysis.
Scheme 3. Electrolysis with acetic acid. Reaction conditions: 1,3-diisopropyl-
benzene (0.2 mL, 1.05 mmol), sodium acetate (300 mg), glacial acetic acid
(15 mL), Pt electrodes (7.5 cm2), 100 mA, 3 h. [b] Conversion determined by
GC–MS analysis.
trode materials and pairings (Table 1, entries 1–5), or the sup-
porting electrolyte (Table 1, entries 5–7). The inclusion of vari-
ous metal salt additives as redox mediators proved to be un-
fruitful, mainly because deposition of the parent metal on the
platinum cathode was observed (Table 1, entries 8–14).
eral other products with identical mass spectra were observed
and no pure product could be obtained, which are assumed to
result from either the isomerization of 1 under the acidic elec-
trolysis conditions or from substitutions affected on the aro-
matic core rather than the benzylic position. While this is a
marked improvement, the relatively large amount of dehydro-
genation product 6 led us to believe that a better nucleophile
might give more satisfactory results by engaging the inter-
mediate carbocations faster, preventing the formation of 6 and
perhaps the other side products as well.
Alternative nitrogen sources were examined next (Table 2).
Acetonitrile was chosen as the solvent and lithium perchlorate
as supporting electrolyte. Neither the anionic (Table 2, entries 1
and 3) nor the cationic (Table 2, entries 2–4) nitrogen sources
Table 2. Electrolysis with alternative nitrogen sources.
Methanol, having the advantage of being quite nucleophilic
and capable of dissolving a wide range of supporting electro-
lytes to permit conduction, was tested next (Scheme 4). Upon
Entry Nitrogen source Supporting Conversion[a,b]
electrolyte
1
2
3
4
NaN3
LiClO4
LiClO4
-
Numerous, non-identifiable products
Numerous, non-identifiable products
Numerous, non-identifiable products
Numerous, non-identifiable products
(NH3OH)2(SO4)
NH4NO3
NH4Cl
LiClO4
[a] Reaction conditions: 250 mA, Pt electrodes (7.5 cm2), 1,3-diisopropyl-
benzene (0.2 mL, 1.05 mmol), LiClO4 (300 mg), nitrogen source (800 mg),
acetonitrile (15 mL), 3 h. [b] Conversion determined by GC–MS analysis.
Scheme 4. Electrolysis with methanol.
electrolysis with methanol as the solvent, the formation of the
dehydrogenation products was completely suppressed result-
ing in the selective formation of the mono- and dimethoxy de-
rivatives 7 and 8, respectively.
Again, the redox potential of 1 and the redox potential of
the supporting electrolyte (KBrO3) were outside the potential
window in cyclic voltammetry measured in the same solvent
(MeOH) as used for preparative electrolysis. These findings are
so far interesting, as they suggest that the nature of the effec-
tive oxidant is not at all simple to determine and fruitful specu-
lation on the exact nature of such a species is, at the moment,
not possible. It seems plausible however to assume the gener-
led to the desired conversion. In all cases numerous, non-iden-
tifiable products were detected during GC–MS analysis.
Cyclovoltammetric investigation showed acetonitrile to be
completely incompatible with the anodic oxidation of 1: no ox-
idation of the aromatic compound was observed before de-
composition of the solvent set in. This suggests that the multi-
ple observed side products, when acetonitrile was used, might
be generated by unspecific reactions of the starting material
and/or the used nitrogen sources (Table 2) with the acetonitrile
decomposition intermediates.
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ChemSusChem 2010, 3, 823 – 828

Electrochemical Functionalization
ation of a bromate derived redox mediator which is crucial to
the successful reaction.[5] The fact that the reaction took place
outside the current window of the solvent offers a ready ex-
planation for the moderate current yields (Table 3). It is, in fact,
surprising that the transformation was quite selective and high
yielding and the current yields were as high as they were.
Next we directed our efforts towards the supporting electro-
lyte. A series of ammonium-based salts and salt mixtures
(Table 4), as well as alkali metal salts (Table 5) were examined.
The tetramethyl- and tetraethylammonium salts (Table 3, en-
tries 1 and 2) continued to show predominant formation of
mono-methoxylated 7 and complete conversion was not ach-
Table 3. Anodic side chain methoxylation of 1: effect of [1] on conversion
Table 4. Screening of various ammonium-based and mixtures of support-
and selectivity.
ing electrolytes.
Entry
[1] [m][a]
Conversion [%][b]
Ratio 7/8[b]
Current yield [%]
Entry Supporting
electrolyte[a]
Conversion[b] Ratio 7/8[b] Comments
[%]
1
2
3
4
0.13
0.20
0.27
0.30
100
80
50
33:67
85:15
100:0
100:0
23
20
14
16
1
2
Me4NBF4
Et4NOTos
80
80
90
40
35
70
50
0
80:20
85:14
50:50
100:0
100:0
70:30
100:0
-
50
3
4
Bu4NClO4
Bu4NBF4
Numerous side products
Traces of monobromide
[a] Reaction conditions: 250 mA, Pt electrodes (7.5 cm2), LiClO4 (300 mg);
nitrogen source (800 mg), methanol (15 mL), 3 h. [b] Conversion and
ratios determined by GC–MS analysis.
5
Bu4NPF6
6
7
8
9
Bu4NHSO4
LiBr/NaIO4
NaClO4/NaNH2
LiClO4/NH4Cl
0
-
10
LiClO4/KOCN 10
100:0
Optimization of the methoxylation of DIPB
[a] Reaction conditions: 250 mA, Pt electrodes (7.5 cm2), 1,3-diisopropyl-
benzene (0.40 mL, 2.11 mmol), methanol (15 mL), 3 h. [b] Conversion and
ratios determined by GC–MS analysis.
Having determined the most promising access to the desired
derivatives of 1, optimization of multiple reaction parameters
was carried out. We first turned our attention to the effect of
the concentration of 1 on the outcome of the reaction
(Table 3; Figure 1). Simply raising the concentration of starting
Table 5. Screening of various alkali metal-based supporting electrolytes.
Entry Supporting Conversion [%][b] Ratio Comments
electrolyte[a]
7/8[b]
1
LiF[c]
0
–
Poor conductivity
2
3
4
LiCl
LiBr
LiI
60
10
0
–
Only monochlorinated
100:0
–
5
6
7
LiClO4
LiBF4
NaF
100
100
0
33:67
60:40 Numerous side products
–
8
9
10
11
12
NaCl
NaClO4
NaIO4
NaBF4
NaOAc
35
100
40
80
40
Traces Only monochlorinated
25:75
90:10 Numerous side products
80:20
100:0 Numerous side products, in-
cluding traces of mono-ace-
toxylated product
13
14
15
16
17
KF
KCl
KClO4
KBF4
KBrO3
80
30
50
30
–
Numerous side products
Traces Only monochlorinated
95:5
100:0
[c]
100
0:100 95%[d]
(80% isolated yield)
Figure 1. Anodic side chain methoxylation of 1: Effect of [1] on current yield.
[a] Reaction conditions: 250 mA, Pt electrodes (7.5 cm2), 1,3-diisopropyl-
benzene (0.40 mL, 2.11 mmol), methanol (15 mL), 3 h. [b] Conversion and
ratios determined by GC–MS analysis. [c] 40 mA. [d] The material con-
tained approximately 5% of an unidentified impurity.
material in the electrolysis cell did not seem to lead in the
right direction. Rather, an increase in concentration shifted the
ratio towards 7 at the expense of the conversion (Table 3),
which was to be expected, as a linear increase in the concen-
tration of 1 with otherwise identical electrolysis conditions led
to a longer amount of time required until the desired diether
8 was formed. The current yield of the reaction, however, was
also adversely affected (Figure 1). The best results were ob-
tained with a concentration of 0.13m.
ieved in the 3 h reaction period. The tetrabutylammonium
salts gave a somewhat more varied picture with conversion
between 35% (Table 4, entry 5) and 90% (Table 4, entry 3).
However, in no case was more dimethoxylated than monome-
thoxylated product obtained. The best results were obtained
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825

G. Hilt, C. Gꢁrtler et al.
with tetrabutylammonium perchlorate, which gave a
ratio of 50:50 (Table 4, entry 3). The use of tetraalkyl-
ammonium salts as supporting electrolyte was not
successful because of electrochemical decomposition
in an undivided cell initiated by a cathodic process to
generate the corresponding trialkyl amines.[6] There-
fore, these cations were disregarded as counter ions,
solubilizing agents, or supporting electrolytes. The
mixed salts (Table 4, entries 7–10) could not provide
any improvement whatsoever and this approach was
deemed to not be feasible.
Figure 2. Screened Alcohols. BDO=1,4-butanediol; EGE=2-ethoxyethanol;DEGME=di-
ethyleneglycol monoethyl ether; TEGME=triethyleneglycol monoethyl ether.
current was observed. We theorized that the difficulty might
lie with the solubility of potassium bromate in the considerably
The lithium salts (Table 5, entries 1–6) also gave a wide
range of results, with the best being the previously mentioned
perchlorate (Table 5, entry 5). In the other cases, either conver-
sion was poor (Table 5, entries 1, 3, 4), the mono- to disubsti-
tuted ratio was unfavorable (Table 5, entry 6), or side product
formation was observed (Table 5, entries 2 and 6). The use of
sodium perchlorate (Table 5, entry 9) led to a further improve-
ment with a ratio of 1:3 with complete conversion of the start-
ing material. The other sodium salts were rather disappointing
either showing poor conversion (Table 5, entries 7, 10 and 12),
poor selectivity (Table 5, entry 11), or formation of significant
amounts of side products (Table 5, entries 8, 10, and 12). Final-
ly, a series of potassium salts were screened toward their ap-
plicability as supporting electrolytes. The initial results (Table 5,
entries 13–16) seemed to mirror those observed when using
lithium or sodium salts again, resulting in unsatisfactory con-
versions, selectivity, and numerous undesired products. Potassi-
um bromate (Table 5, entry 17), however, demonstrated the
exact reactivity profile we had been waiting for.
less polar alcohols. Multiple strategies were envisaged to
bypass this dilemma and to improve overall conductivity: addi-
tion of various additives, applying varying ratios of alcohols
and co-solvents, and deprotonation of the alcohols themselves
to increase the overall polarity of the reaction mixtures.
Acetic acid and phosphoric acid were envisaged as possible
additives. Disappointingly, addition of acetic acid leads to no
improvement in conductivity. Upon addition of phosphoric
acid to DEGME, immediate discoloration and turbidation of the
solution were observed. Decomposition seems to have oc-
curred, effectively ending further attempts along this route.
Using MeOH as solvent or co-solvent with the ethylene
glycol derivatives was initially encouraging, as it immediately
led to much improved conductivity, as well as quite high con-
version rates. Unfortunately, the ethylene glycol ethers greatly
hindered the purification of the obtained compounds. In only
one case was the tentative assignment of the obtained com-
pounds possible: when using a 1:1 ratio of MeOH and DEGME
59% 8 and at most, approximately 40% of mixed monome-
thoxy/DEGME diether (of type 9) was generated. However, in
all cases, it was not possible to achieve acceptable separation
from the applied ethylene glycol, although conversion rates
were acceptable. When higher ratios of MeOH were used, only
8 was synthesized with traces of mono-ethylene glycolated
products. Using an alternative, unreactive solvent, such as 1,2-
dimethoxy ethane (DME) and 5 equivalents of the respective
alcohols led to a renewed loss of conductivity.
Complete conversion was paired with strong preference for
the bis-alkoxylated product. Upon work-up, excellent yields of
8 were achieved. Yields of >99% with about 95% purity, as
determined by NMR analysis of the crude product, were regu-
larly attained. The isolated yield was also good with 80% of 8
obtained. The discrepancy between the crude and the isolated
yield suggests that perhaps the product underwent decompo-
sition when purified by chromatographic methods. We revisit-
ed the glassy carbon electrodes with the newly determined
optimal parameters and were pleased to note that similar
yields and purities were obtainable. A short experiment deter-
mined that an increase in substrate concentration under these
conditions was possible without great difficulty: when apply-
ing 1 (14 mmol) in methanol (20 mL), the product was generat-
ed in good yield (76%) with traces of non-identifiable impuri-
ties, irrespective of which of the two electrode materials was
selected.
Attempts at utilizing various alkali metal hydrides and butyl
lithium as bases to generate the alkoxide species led to the de-
sired conductivity in all cases; however in the majority of
cases, either a low conversion rate or the formation of numer-
ous side products was observed.
Transetherification
Considering the difficulties and ambiguities encountered in the
attempt to directly functionalize 1 with other alcohols in a
smooth and straightforward course of the electrolysis in meth-
anol, we decided to explore the possibility of attaining the de-
sired products continuing from 8 (Scheme 4).[7] A slightly differ-
ent selection of alcohols was screened (Table 6). The general
features of the transetherification are that it should occur via a
SN1 mechanism, thus suggesting the use of the alcohols them-
selves as solvents, where applicable. Furthermore, addition of
either Brønsted or Lewis acids was deemed to be necessary to
enable the smooth formation of the intermediate carbocation.
Anodic oxidations with further alcohols
Having found a satisfactory set of conditions leading to the de-
sired bis-methoxylated derivative 8, our next step was to at-
tempt functionalization of 1 with further alcohols. A brief
screening of readily available alcohols was carried out; the
tested compounds are presented in Figure 2.
No conversion could be obtained with all of the alcohols
presented in Figure 2, presumably because in each case, no
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ChemSusChem 2010, 3, 823 – 828

Electrochemical Functionalization
spite the inherent problem of side reactions presented by the
fundamental nature of the SN1 reaction.
Table 6. Diethers generated by the transetherifiction reaction.
Entry Screened alcohol[a]
Reaction time Ratio
Yield of 10[c]
[d]
9/10/11[b]
1
2
3
4
5
6
7
8
ethanol
2.5
1.5
3.5
5.5
3.5
3.5
4.5
11:72:17
6:83:11
7:85:8
62%
45%
40%
Conclusions
allyl alcohol
n-butanol
2-propanol
benzyl alcohol
DEGME
phenol[f]
4-methoxy phenol[f] 4.5
[d]
We have demonstrated a short and simple preparative proce-
dure to convert the unreactive, unfunctionalized 1,3-diisopro-
pylbenzene to the dimethoxy derivative 8 by anodic oxidation
in methanol with the addition of potassium bromate. A variety
of solvents, nucleophiles, electrode materials, and additives
were screened during the optimization process. Scale-up ex-
periments into the gram range were also successfully carried
out. The electrochemical conversion in methanol resulted in
high yields and excellent chemoselectivity, eliminating the
need for further purification for most purposes.
/
/
0:74:26[e]
38%
0:0:100[e]
26% only 11
[d]
/
/
/
[d]
/
[a] Reaction conditions: 8 (1.0 mmol), alcohol (6.0 mL), methane sulfonic
acid (0.32 mL), ambient temperature. [b] Determined by GC–MS analysis.
[c] Isolated yield. [d] Only elimination products observed. [e] Determined
from the isolated compounds. [f] The alcohol (8 equivalents) was dis-
solved in THF (3 mL).
While attempts to directly functionalize 1,3-diisopropylben-
zene with further alcohols were not met with success, the sub-
sequent derivatization continuing from 8 was readily achieved
with a selection of alcohols. Thus, the generation of a small
family of diether compounds was easily achieved.
Our first attempts to accelerate the reaction by heating the
reaction mixture led to preferred formation of the double elim-
ination product 1,3-bis-(prop-2-enyl)-benzene, as expected
from a classic, clear-cut SN1 scenario (Scheme 5). Borontrifluor-
ide etherate, and titanium tetrachloride were tested and while
they led to formation of the desired diethers 10, they also gen-
erated substantial amounts of elimination products 11 and
mono-methoxy ethers 9.
Experimental Section
Anodic oxidation of 1,3-diisopropylbenzene 1 to 1,3-bis(1-me-
thoxy-1-methylethyl)benzene 8: 1,3-diisopropylbenzene 1 (0.40 mL,
0.34 g, 2.11 mmol) was added to a suspension of potassium bro-
mate (0.60 g, 3.59 mmol) in methanol (15 mL) using a double-
walled water-cooled glass beaker cell with a Teflon stopper. A cur-
rent of 250 mA was applied to the respective electrodes (platinum/
platinum (7.5 cm2) or glassy carbon/glassy carbon (6 cm2)) until
conversion was determined to be complete by GC–MS analysis.
The reaction mixture was partitioned between water (30 mL) and
methyl-tert-butyl ether (30 mL). The aqueous phase was extracted
twice with methyl-tert-butyl ether (30 mL) and the combined or-
ganic phases were washed once with water (30 mL) and brine
(15 mL) and dried over magnesium sulfate. The solvent was re-
moved under reduced pressure. The obtained crude 8 (466 mg,
2.10 mmol, >99% with trace impurities) was purified by column
chromatography (eluent: diethyl ether/pentane 1:9). Purified 8 was
obtained as a clear, pale yellow oil (373 mg, 1.68 mmol, 80%).
1H NMR (300 MHz, CDCl3): d=7.48–7.47 (m, 1H), 7.34–7.26 (m,
3H), 3.07 (s, 6H), 1.53 ppm(s, 12H). 13C NMR (75 MHz, CDCl3): d=
146.1, 128.2, 124.5, 123.4, 77.1, 50.8, 28.2. ppm. ESI(+)-HRMS:
C14H22NaO2 (M+Na+) calc. 245.1517; found 245.1512.
Scheme 5. Transetherification reaction.
Methane sulfonic acid was used as a Brønsted acid and re-
sulted in moderate to acceptable yields of products of type 10
when primary alcohols were used (Table 6, entries 1–3, 5). The
notable exception was DEGME, which led exclusively to the
unsaturated product of type 11. When secondary alcohols
(Table 6, entry 4) or phenol derivatives (Table 6, entries 7 and 8)
were applied, only elimination products were observed. The
major difficulties stemmed from the very mechanism of the re-
action itself. The reaction resulted in varying quantities of ole-
fins of type 11; mixed diethers of type 9 were rarely observed
in significant amounts but were present none the less.
General procedure for the transetherification reaction: 1,3-bis(1-
methoxy-1-methylethyl)benzene 8 (222 mg, 1 mmol) was dissolved
in the respective alcohol (6 mL; in the case of solid alcohols, as in
Table 6, entries 7 and 8, the alcohols (8 equivalents) were dissolved
in THF), and methane sulfonic acid (0.32 mL, 386 mg, 4 mmol) was
added dropwise. The reaction mixture was stirred at ambient tem-
perature until conversion was deemed complete by GC–MS analy-
sis. The reaction mixture was partitioned between water (10 mL)
and methyl-tert-butyl ether (10 mL). The aqueous phase was ex-
tracted twice with methyl-tert-butyl ether (10 mL) and the com-
bined organic phases were washed once with water (10 mL) and
brine (5 mL) and dried over magnesium sulfate. The solvent was re-
moved under reduced pressure. The obtained crude products were
purified by column chromatography.
Nevertheless, the methodology presented herein permits a
smooth introduction of functionality by using a combination
of electrochemical activation of a previously non-reactive sub-
strate and subsequent introduction of alternative alcohols, de-
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827

G. Hilt, C. Gꢁrtler et al.
1,3-bis(1-ethoxy-1-methylethyl)benzene: Diethyl ether/pentane
(1:19) was used as eluent. The product was obtained as a clear,
pale yellow oil (154 mg, 0.62 mmol, 62%).
1H NMR (300 MHz, CDCl3): d=7.53–7.50 (m, 1H), 7.29–7.27 (m,
3H), 3.21 (q, J=7.0 Hz, 4H), 1.54 ppm(s, 12H), (t, J=7.0 Hz, 6H).
13C NMR (75 MHz, CDCl3): d=146.8, 128.1, 124.28, 123.2, 76.9, 58.3,
28.8, 16.1 ppm. ESI(+)-HRMS: C16H26NaO2 (M+Na+) calcd. 273.1830;
found 273.1825.
Acknowledgements
Financial support for M. Bohn by the Bayer MaterialScience AG is
gratefully acknowledged.
Keywords: alcohols · electrochemistry · functionalization ·
oxidation · transetherification
1,3-bis[1-(allyloxy)-1-methylethyl]benzene: Diethyl ether/pentane
(1:19) was used as eluent. The product was obtained as a clear,
pale yellow oil (123 mg, 0.45 mmol, 45%).
1H NMR (300 MHz, CDCl3): d=7.56–7.51 (m, 1H), 7.34–7.27 (m,
3H), 5.91 (ddt, J=5.4, 10.5, 17.1 Hz, 2H), 5.28 (ddt, J=1.7, 3.5,
17.1 Hz, 2H), 5.13 (ddt, J=1.5, 3.0, 10.3 Hz, 2H), 3.70 (ddd, J=1.5,
1.6, 5.4 Hz, 4H), 1.56 ppm(s, 12H). 13C NMR (75 MHz, CDCl3): d=
146.5, 135.9, 128.2, 124.4, 123.3, 116.0, 77.4, 64.5, 28.7 ppm. ESI(+)-
HRMS: C18H26NaO2 (M+Na+) calcd. 297.1830; found 297.1825.
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Chapt. 13, 4th Edition, Dekker, NY, 2001, pp. 471–498, and references
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1,3-bis(1-butoxy-1-methylethyl)benzene: Diethyl ether/pentane
(1:19) was used as eluent. The product was obtained as a clear,
pale yellow oil (123 mg, 0.40 mmol, 40%).
1H NMR (300 MHz, CDCl3): d=7.52–7.49 (m, 1H), 7.30–7.25 (m,
3H), 3.14 (t, J=6.7 Hz, 4H), 1.61–1.43 (m, 4H), 1.53 (s, 12H), 1.33
(m, 4H), 0.87 ppm(t, J=7.3, 6H). 13C NMR (75 MHz, CDCl3): d=
146.7, 127.9, 124.3, 123.5, 76.6, 62.7, 32.8, 28.7, 19.7, 14.2 ppm.
ESI(+)-HRMS: C20H34NaO2 (M+Na+) calcd. 329,2457; found
329.2451.
1,3-bis[1-(benzyloxy)-1-methylethyl]benzene: Diethyl ether/pentane
(1:19) was used as eluent. Reaction carried out at half-scale. The
product was obtained as
(0.19 mmol, 38%).
a clear, pale yellow oil (73 mg
1H NMR (300 MHz, CDCl3): d=7.69–7.66 (m, 1H), 7.45–7.22 (m,
13H), 4.25 (s, 4H), 1.65 ppm(s, 12H). 13C NMR (75 MHz, CDCl3): d=
146.4, 139.6, 128.5, 128.3, 127.6, 127.4, 124.8, 123.7, 77.5, 65.4,
28.8 ppm. ESI(+)-HRMS: C26H30NaO2 (M+Na+) calcd. 397.2143;
found 397.2138.
1-{1-[2-(2-ethoxyethoxy)ethoxy]-1-methylethyl}-3-isopropenylben-
zene: Diethyl ether/pentane (4:6) was used as eluent. This reaction
was carried out at half-scale. The unsaturated product was ob-
tained as a clear, pale yellow oil (39 mg, 0.13 mmol, 26%).
1H NMR (300 MHz, CDCl3): d=7.57–7.52 (m, 1H), 7.38–7.23 (m,
3H), 5.39–5.35 (m, 1H), 5.11–5.06 (m, 1H), 3.66–3.56 (m, 6H), 3.52
(q, J=14.1 Hz, 2H), 3.35 (t, J=5.6 Hz, 2H), 2.19–2.14 (m, 3H), 1.55
(s, 6H), 1.20 ppm(t, J=7.0 Hz, 3H). 13C NMR (75 MHz, CDCl3): d=
146.3, 143.7, 141.3, 128.2 125.2, 124.3, 123.3, 112.6, 77.04, 70.9,
70.1, 66.8, 62.5, 28.6, 22.1, 15.4 ppm. ESI(+)-HRMS: C18H28NaO3
(M+Na+) calcd. 315.1936; found 315.1935.
Received: February 17, 2010
Revised: March 16, 2010
Published online on May 12, 2010
828
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