A synthetic route to 1-(4-boronobenzyl)-1H-pyrrole

Article abstract of DOI:10.1177/1747519820960692

The synthesis of 1-(4-boronobenzyl)-1H-pyrrole was investigated using three different routes. Two key routes that involved the introduction of the boronate group protected as the pinacol ester, failed, due to deprotection problems. The route involving the

Full text of DOI:10.1177/1747519820960692

960692CHL0010.1177/1747519820960692Journal of Chemical ResearchD’Silva and Walker
research-article2020
Research Paper
Journal of Chemical Research
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A synthetic route to 1-(4-boronobenzyl)-
1H-pyrrole
https://doi.org/10.1177/1747519820960692
DOI: 10.1177/1747519820960692
journals.sagepub.com/home/chl
Claudius D’Silva
Abstract
The synthesis of 1-(4-boronobenzyl)-1H-pyrrole was investigated using three different routes. Two key routes that
involved the introduction of the boronate group protected as the pinacol ester, failed, due to deprotection problems.
The route involving the introduction of the boronate group as the final step of the reaction yielded 1-(4-boronobenzyl)-
1H-pyrrole (10).
Keywords
boronate esters, boronic acid, lithiation, pinacol protection, pyrrole
Date received: 4 August 2020; accepted: 2 September 2020
OH
OH
OH
OH
O
B
C
HO
O
N
1
B
O
5
B
H3C
x
OH
N
H2N
+
B
Br
MeO
OMe
O
OH
10
described a procedure to arylmethylene pyrroles based on
the reduction of acylpyrroles with (BF3.OEt2)/NaBH4
(Scheme 1(b))31 and in a further paper32 a high yield route to
N-alkyl pyrroles using the Paal–Knorr method, involving
the condensation of primary amines with 2,5-dimethoxytet-
rahydrofuran (DMT)20,33,34 using acid-base organic solvent
mixtures (Scheme 1(c)).
In an attempt to combine the thin film forming proper-
ties of pyrroles25 with our interest in boronates35,36 as recep-
tors and sensors,37,38 we now report strategies directed to
the synthesis of 1-(4-boronobenzyl)-1H-pyrrole (10).
Introduction
Pyrrole/pyrrole derivatives have been investigated for a
variety of uses which include batteries,1–3 an anti-corrosion
film,4–6 photoconductors,6,7 conducting polymers,1–3,8 elec-
tromagnetic shielding materials,9 membranes,10,11 ion-
exchange chromatography resins,12 modified electrodes for
enantioselective recognition,13 electrosynthesis,14–16 dis-
plays,17 tissue engineering scaffolds,18,19 neural probes,20
drug delivery devices,21 biosensors22–24 and sensors.25 The
preparation of N-substituted pyrroles traditionally has
involved deprotonation of the 1-position of the pyrrole ring
with Na, K26–28or n-BuLi7,8 under nitrogen in a solution of
tetrahydrofuran (TFH) or under phase transfer conditions
with t-BuOK29 or NaOH30 followed by reaction of the alkali
salt of pyrrole, with an equivalent amount of acyl or alkyl
halide (Scheme 1(a)). The above reactions, due to the use of
basic conditions, the reactivity of pyrrole and activation
effects have synthetic limitations, low yields due to the for-
mation of undesirable side products (2-substituted and dis-
ubstituted pyrroles)26–28 and are unsuitable in the preparation
of pyrroles containing base labile groups. Recently, we
Department of Chemistry and Materials, Faculty of Science and
Engineering, The Manchester Metropolitan University, Manchester, UK
Corresponding author:
Claudius D’Silva, Department of Chemistry and Materials, Faculty of
Science and Engineering, The Manchester Metropolitan University, John
Dalton Building, Chester Street, Manchester M1 5GD, UK.
Email: c.dsilva@ymail.com
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2
Journal of Chemical Research 00(0)
/tol
O
HO
HO
O
O
OH
AIBN/CCl4
HO
Na, K, n-BuLi
t-BuOK
R-X
CH3
CH3
B
CH2
Br
B
B
a
O
6
7
N
R
N-
N
M+
OH /tol
HO
HO
:/n-BuLi/THF
O
O
O
O
CH2
N
B
CH2
N
B
CH2
Br
B
X
N
BF3OEt/NaBH4
HO
RCOCl/DMAP
b
10
5
8
N
N
N
Scheme 3. A synthetic pathway to 10 via the alkylation of the
lithium salt of pyrrole.
R
O
R
Pyr/AcOH
RNH2
+
c
OH
N
N
OMe
H2
+
N
t-BuLi/B(OMe) 3
H+/ H2O
AcOH/Pyr
B
MeO
Br
N
R
O
Br
MeO
OMe
OH
O
10
9
Scheme 4. Synthesis of 1-(4-boronobenzyl)-1H-pyrrole (10).
Scheme 1. Synthetic routes to N-alkyl pyrroles.
DMAP: dimethyaminopyridine; n-BuLi: n butyllithium; t-BuOK:
potassium tert-butoxide; NaBH4: sodium borohydride; BF3OEt:
boron trifluoride diethyl etherate pyr-pyridine; AcOH: acetic acid.
was successfully reduced to 4-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl) benzyl)-1H-pyrrole (5) using BF3/OEt2/
NaBH4.31 Cleavage of the cyclic boronate ester 5 was
41
/tol
O
attempted using 4M HCl, RT, 18h,35 BBr3/CH2Cl2 and
O
O
O
O
HO
HO
O
O
OH
P(Ph)3/CCl4
HO
C
C
B
C
B
B
MeOH/TsOH/reflux, but all methods failed to yield the
desired product 10, due to decomposition of the pyrrole
group. Milder methods SiO2/CH2Cl2/(COOH)2,42 basic
hydrolysis (dioxane/NaOH(aq)) and oxidative cleavage
(NaIO4/Me2CO/aq. NH4OAc)43 also failed to yield 10.
In a parallel approach, the preparation 1-(4-boronobenzyl)-
1H-pyrrole (10) was investigated as shown in Scheme 3.
4-Methylbenzeneboronic acid was protected with ethylene
glycol as the cyclic boronate ester 6 and isolated in good yield
(83%). Bromination of 6 with N-bromosuccinimide (NBS) in
the presence of azoisobutyronitrile (AIBN) in refluxing car-
bon tetrachloride afforded 2-(4-(bromomethyl)phenyl)-1,3,2-
dioxaborolane (7), in high yield (90%). 2-(4-(Bromomethyl)
phenyl)-1,3,2-dioxaborolane (7) was converted to the cyclic
pinacol ester 8 in moderate yield (50.5%) by exchange with
pinacol, in refluxing toluene. 2-(4-(Bromomethyl)phenyl)-
4,4,5,5-tetramethyl-1,3,2- dioxaborolane (8) was converted
to 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)-
1H-pyrrole (5) in moderate yield (34%), by alkylation of the
lithium salt of pyrrole in dimethyl sulfoxide (DMSO), pre-
pared with n-BuLi/THF. Cleavage of the cyclic boronate ester
(5: Scheme 3) as in the case of (5: Scheme 2) failed to yield
10 using similar procedures.
The inability of the synthetic routes depicted in Schemes 2
and 3 to produce 1-(4-boronobenzyl)-1H-pyrrole (10) led to
the investigation of an alternative approach to the product, in
which the boronate group was introduced late in the reaction,
as shown in Scheme 4. In this approach, 4-bromobenzylamine
was condensed with DMT under neutral conditions in an
aqueous mixture of AcOH/pyr to give 1-(4-bromobenzyl)-
1H-pyrrole (9).32 Lithiation of 9 with t-butyllithium, quench-
ing with trimethylborate followed by acid hydrolysis finally
yielded 1-(4-boronobenzyl)-1H-pyrrole (10) (52%) in moder-
ate yield. Confirmation of the structure of (10) using mass
spectroscopic techniques proved inconclusive as the molecu-
lar ion was not directly observed based on the technique used,
due to the elimination of H2O from the –B(OH)2 group.35 In
EIMS, a distinct peak was observed at 182 for (M+-H2O+1)
OH
OH
Cl
2
3
1
/DMAP/CHCl3
N
O
C
O
O
O
O
HO
HO
BF3OEt2/NaBH4
THF
CH2
N
B
CH2
N
B
B
X
N
4
5
10
Scheme 2. A synthetic pathway to 10 via the reduction of
acyl pyrrole.
Results and discussion
The synthesis of pyrrole/boronate compounds is problematic
due to the sensitivity of the pyrrole group to undergo oxida-
tion under acidic conditions leading to uncontrolled poly-
merisation and decomposition39 and the aqueous solubility
of the boronate group which may necessitate its protection,
to facilitate isolation and characterisation.
Our strategy to the synthesis of 1-(4-boronobenzyl)-
1H-pyrrole (10) is outlined in Scheme 2, and involved the
introduction of the boronate group early in the reaction, pro-
tected as a pinacol ester due to stability problems associated
with the ethylene glycol group.35 4-Carboxybenzeneboronic
acid (1) was converted to the pinacol ester in refluxing tolu-
ene (Dean–Stark apparatus) in quantitative yields to give the
cyclic boronate ester 2 in high yield (98%). The attempted
conversion of the pinacol protected acid 2, to the acid chlo-
ride (3) using thionyl chloride or oxalyl chloride failed to
yield the desired product due to the stability of the pinacol
protecting group. The milder procedure of Lee40 using triph-
enylphosphine/carbon tetrachloride yielded the crude acid
chloride 3 on solvent evaporation as a mixture contaminated
with the pinacol protected acid 2 and triphenylphosphine.
Due to the moisture sensitivity of 3, the compound was used
as isolated and reacted with pyrrole, using dimethylamino-
pyridine (DMAP) as an acylation catalyst to yield the
N-acylpyrrole 4, in low yield (24%). The N-acylpyrrole 4

D’Silva
3
and in negative ion ESMS peaks at 437 for (2M++Cl) and
236 (M++Cl). Definitive confirmation of the structure of
compound 10 was finally achieved by its conversion to the
pinacol ester 5 (69%) in high yield.
J=8.1); 13 C NMR (67.8MHz, CDCl3): δ 25.1, 85.5, 129.4,
131.7, 135.0; LRMS (CIMS (NH3)) m/z (%): 266 ((M+
NH4)+, 77), 162 (22), 144 (27), 136 (100), 126 (16); calcd for
C13H17O4 B: C, 62.87; H, 6.91; found: C, 63.06; H, 7.15.
In conclusion, a variety of methods have been investi-
gated to synthesise 1-(4-boronobenzyl)-1H-pyrrole (10). It
is clear based on the results reported here that the introduc-
tion of the boronate group, late in the reaction, is the most
effective method for the preparation of this compound
(Scheme 4) due to the lack of an adequate method for the
removal of the pinacol protecting group from 5 (Schemes 2
and 3). Review of the literature identified that the carbazole
analogue of 10, 4-((9H-carbazol-9-yl)methyl)phenylbo-
ronic acid44 had been prepared from the corresponding car-
bazole analogue of 9, 9-(4-bromobenzyl)-9H-carbazole
using a similar procedure to Scheme 4, but n-butyllithium(n-
BuLi) replaced t-butyllithium(t-BuLi).
4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-
yl)benzoyl chloride (3)
A mixture of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
2-yl)benzoic acid (2) (2g; 8.1mmol), triphenylphosphine
(2.1g; 8.1mmol), in CCl4 (50mL) were refluxed for 20h,
then cooled, filtered and evaporated to give crude
4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzoyl
chloride as an oil: Yield 2.24g.
4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-
yl)phenyl)(1H-pyrrol-1-yl)methanone (4)
Prepared by the DMAP (0.099g; 0.81mmol) catalysed con-
densation of crude 4-(4,4,5,5-tetramethyl-1,3,2-dioxab-
orolan-2-yl)benzoyl chloride (3) (2.24g; 8.4mmol) with
pyrrole (0.62g; 9.26mmol) in the presence of triethylamine
(TEA) (1.3mL; 9.1mmol)/CH2Cl2 (6mL) overnight,
according to the general procedure described by D’Silva
and Iqbal.31 After work up, the crude product was purified
by PTLC (CHCl3 /pet ether (40–60); 1:1) to give a colour-
less solid. Yield 0.59g (24%); m.p. 99°C–102°C; 1H NMR
(270MHz, CDCl3): δ 1.5 (s, 12H), 6.45 (t, 2H, J=2.5), 7.35
(t, 2H, J=2.5), 7.8 (d, 2H, J=8.8), 8.05 (d, 2H, J=8.8); 13
C NMR (67.8MHz, CDCl3) δ 24.89, 29.69, 113.1, 121.2,
128.4, 134.7; LRMS (CIMS (NH3)) m/z (%): 315 ((M+
NH4)+, 37), 298 ((M+H+), 43), 279 (10), 247 (18), 231
(18), 198 (10), 189 (86), 172 (100), 158 (18), 152 (15), 144
(94), 136 (21), 128 (24); calcd for C17H20 NO3 B: C, 68.65;
H, 6.78, N, 4.71; found: C, 68.73; H, 6.88; N, 4.67.
Experimental section
Trimethylborate, tert-butyllithium (1.7M in pentane), n-butyl-
lithium (1.6M in hexane), pinacol, DMAP, 4-bromoben-
zylamine.HCl, pyrrole, pyridine, DMSO, THF (Aldrich),
4-Carboxybenzeneboronic acid (Lancaster). Commercial rea-
gents were used as received with the exception of pyrrole,
pyridine and THF, which were redistilled the latter from
sodium and benzophenone under nitrogen. Reactions on
exclusion of air or water were performed in oven-dried glass-
ware and under an argon or N2 atmosphere. Analytical thin-
layer chromatography was performed on Merck silica gel
60F254 aluminium backed thin-layer chromatography (TLC)
plates and was visualised by fluorescence quenching under
UV light or I2 staining. Preparative thin-layer chromatogra-
phy (PTLC) was performed on Analtech silica gel GF
2000μm and was visualised by fluorescence quenching under
UV light. Melting points were determined on an electrother-
mal apparatus and were reported uncorrected. 1H and 13C-
NMR spectra were recorded at 270.05 and 67.80MHz,
respectively, on a Joel 270 MHz FT-NMR spectrometer using
TMS as an internal standard. Mass spectra were recorded by
B. Stein at the EPSRC Mass Spectrometry Service Centre,
Swansea for EI and CI (NH3) spectra, on a VG quarto II triple
quadropole mass spectrometer and accurate mass liquid sec-
ondary ion mass spectrometry (LSIMS) measurements on a
Finnigan MAT 900 XLT using a Cs+ ions to ionise. Elemental
analysis was performed at the Micro Analytical Service,
Manchester Univ, UK. Distance calculations in optimised
structures were undertaken using the Alchemy 2000 (Tripos)
molecular modelling package.
4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-
yl)benzyl)-1H-pyrrole (5: Scheme 2)
4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)
(1H-pyrrol-1-yl)methanone(4) (0.5g; 1.7mmol) was reduced
to (5a) in THF (3mL) using NaBH4 (0.3g) in the presence of
BF3: OEt2 (2.3g; 16.3mmol) in a sealed pressure tube.31 The
crude product was obtained as an oil which was purified by
PTLC (EtOAc/CHCl3 /pet ether (40–60); 1:4:5) to give a col-
ourless crystalline solid. Yield 0.11g (24%); m.p. 123°C–
125°C; 1H NMR (270MHz, CDCl3): δ 1.3 (s, 12H), 5.1 (s,
2H), 6.2 (t, 2H, J=2.1), 6.7 (t, 2H, J=2.1), 7.1 (d, 2H,
J=7.8), 7.8 (d, 2H, J=7.8); 13 C NMR (67.8MHz, CDCl3):
δ 24.6, 53.2, 83.6, 108.3, 121.0, 126.1, 135.0, 141.0; LRMS
(EIMS) m/z (%) 283 ((M+) 38), 217 (100), 182 (10), 135
(11), 117 (55), 91 (10); HRMS (EIMS) calcd for C17H22 NO2
B 283.1744, found: 283.1744; calcd for C17H22 NO2 B: C,
72.04; H, 7.83, N, 4.95; found: C, 72.14; H, 8.02; N, 5.04.
4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-
yl)benzoic acid (2)
Amixtureof4-carboxybenzeneboronicacid(0.5g;3.0mmol)
and 2,3-dimethyl-2,3-butanediol (0.36g; 3.0mmol) was sus-
pended in toluene (100mL) and refluxed in a Dean–Stark
apparatus until the theoretical amount of water was removed.
The solution was then evaporated to yield on recrystallisati-
ion from CH3CN a colourless solid. Yield 0.78g (98%); m.p.
230°C–232°C (lit.45 228°C–231°C); 1H NMR (270MHz,
CDCl3): δ 1.5 (s, 12H), 7.9 (d, 2H, J=8.1), 8.15 (d, 2H,
4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-
yl)benzyl)-1H-pyrrole (5: Scheme 3)
To a stirred solution of pyrrole (0.4g; 5.93mmol) dissolved
in dry THF (3mL), under nitrogen at 0°C was added
n-BuLi (3.37mL; 5.39mmol) and the solution stirred for

4
Journal of Chemical Research 00(0)
2h. The solvent was then removed and a solution of x M+-2Br), 100), 333(25), 296 (45), 281/283 (55),
2-(4-(bromomethyl)phenyl)-1,3,2-dioxaborolane (1.6g; 247/248/249 (22), 232/233 (62); HRMS (EIMS) calcd for
5.39mmol) added dropwise and left stirring for 8h at 65°C. C13H18O2 BBr 296.0583; found: 296.0583; calcd for
Water was then added and the solution extracted with Et2O, C13H18O2BBr: C, 52.69; H, 6.13; found: C, 52.79; H, 6.22.
dried MgSO4 and evaporated to yield an oil which was
purified 2× by PTLC (CHCl3) to yield a solid (0.52g;
34%). 1H NMR (270MHz, CDCl3) δ 1.3 (s, 12H), 5.1 (s,
1-(4-Bromobenzyl)-1H-pyrrole (9)
2H), 6.2 (t, 2H, J=2.1), 6.7 (t, 2H, J=2.1), 7.1 (d, 2H, Prepared by acid-base catalysed condensation of 4-bro-
J=7.8), 7.75 (d, 2H, J=7.8); 13 C NMR (67.8MHz, CDCl3) mobenzylamine.HCl (3g; 16.1mmol) with DMT (2.1mL;
δ 24.6, 53.2, 83.6, 108.3, 121.0, 126.1, 135.0, 141.0; LRMS 16.2mmol) in pyridine/AcOH/H2O at 70°C for 50h as
(EIMS) m/z (%) 283 ((M+) 54), 217 (100), 182 (22), 135 described by D’Silva and Walker.32
(18), 117 (94), 91 (15); HRMS (EIMS) calcd for C17H22
NO2 B: 283.1744; found: 283.1744.
1-(4-Boronobenzyl)-1H-pyrrole (10)
To a stirred solution of 1-(4-bromobenzyl)-1H-pyrrole (9)
2-p-Tolyl[1,3,2]dioxaborolane (6)
(2.0g; 9.0mmol), dissolved in THF (8mL) under argon at
A mixture of 4-methylphenylboronic acid (5.1g; 38.0mmol) −60°C was added dropwise t-BuLi (11.0mL; 19mmol).
and ethylene glycol (2.36g; 38.0mmol) was suspended in After 1h at −60°C, THF (6mL) and trimethyl borate (10mL;
toluene (100mL) and refluxed in a Dean–Stark apparatus 88mmol) were added to the dark brown solution and it
until the theoretical amount of water was azeotroped. The allowed to reach room temperature overnight. Then HCl
solution was then evaporated to recover a colourless solid (2M) was added and the solution left stirring for 4h fol-
(5.13g; 83%). m.p. 61°C–63°C. Lit.46 59°C–60°C. 1H lowed by extraction with CHCl3. The CHCl3 layer was then
(270MHz, CDCl3) δ 2.4 (s, 3H), 4.4 (s, 4H), 7.3 (d, 2H, washed with NaOH (2M). The NaOH layer was then acidi-
J=7.5), 7.75 (d, 2H, J=7.5); 13 C NMR (67.8MHz, CDCl3) fied and the product extracted into the CHCl3 layer, washed
δ 22.1, 65.5, 128.8, 135.0, 140.1; LRMS (EIMS) m/z (%) with water, dried MgSO4 and evaporated to yield a brown
162 ((M+), 100), 132 (30), 117 (70), 105 (40), 91 (37); calcd oil which was purified by PTLC (CHCl3/EtOH: 25:1) to
for C9H11O2B: C, 66.63; H, 6.84; found: C, 66.9; H, 7.17.
give on storage an off-white solid. Yield 0.92g (52%); m.p.
131°C–133°C; 1H NMR (270MHz, CDCl3) δ 5.05 (s,
2H), 6.1 (t, 2H, J=2.3), 6.6 (t, 2H, J=2.3), 7.1 (d, 2H,
J=8.2), 8.05 (d, 2H, J=8.2); 13 C NMR (67.8MHz, CDCl3)
δ 53.4, 108.8, 121.3, 126.6, 128.8, 136.1, 143.0; LRMS
2-(4-(Bromomethyl)phenyl)-1,3,2-
dioxaborolane (7)
A mixture of 2-p-tolyl[1,3,2]dioxaborolane (6) (3.15 g; (EIMS) m/z 182 ((M+ -H3O), 5), 157 (50), 117 (28), 91
19.4 mmol), NBS (3.8 g; 21.4 mmol) and AIBN (0.067 g; (100); LRMS (ESMS) m/z (%) 437 (2M++Cl), 50), 282
0.19 mmol) in CCl4 (125 mL) was refluxed for 18 h. The (40), 254 (10), 236 (M++Cl, 50), 127 (100), 81 (82).
solution was then cooled, filtered and evaporated to give Confirmation of the structure of the compound was achieved
a brown solid which was decolourised with CHCl3\char- by converting (7) (0.2g; 1.0mmol) into 4-(4,4,5,5-tetrame-
coal to yield after hot filtration and evaporation a pale thyl-1,3,2-dioxaborolan-2-yl)benzyl)-1H-pyrrole (5a) by
brown solid. Yield 4.21 g (90%); m.p. 142 °C–143 °C reaction with pinacol (0.11g; 1.0mmol) with removal of
(lit47 84 °C–85 °C); 1H NMR (270 MHz, CDCl3) δ 4.15 water using a Dean–Stark apparatus and PTLC (CH2Cl2).
(s, 4H), 4.3 (s, 2H), 7.2 (d, 2H, J = 7.9), 7.65 (d, 2H, The compound was obtained as a colourless solid. Yield
J = 7.9); 13 C NMR (67.8 MHz, CDCl3) δ 33.1, 66.0, (69%); m.p. 117°C–121°C; 123°C–125°C (5a); LRMS
128.3, 135.2, 140.8; LRMS (EIMS) m/z (%) 240 ((M+), (EIMS) m/z (%) 283 ((M+) 53), 217 (100), 182 (22), 135
2), 239 ((M+-H)+), 3), 161 (100), 117 (24), 105 (10), 91 (18), 117 (100), 91 (15); HRMS calcd for C17H22 NO2 B:
(12), 86 (16); calcd for C9H10O2 BBr: C, 44.9; H, 4.2; 283.1744; found: 283.1744.
found: C, 44.73; H, 4.09.
Acknowledgement
The author thanks Dr. Deborah A Walker for her contribution to
this paper.
2-(4-(Bromomethyl)phenyl)-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane (8)
A mixture of 2-(4-(bromomethyl)phenyl)-1,3,2-dioxab-
orolane (7) (1.94g; 16.0mmol) and pinacol (1.94g;
16.0mmol) was suspended in toluene (100mL) and
refluxed in a Dean–Stark apparatus for 20h. The solution
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect
to the research, authorship and/or publication of this article.
was then evaporated to recover a brown solid. Yield 2.4g
(51%); m.p. 71°C–75°C. Lit48 85°C–89°C. An analytical
sample was prepared by decolourisation of the compound
with charcoal in CHCl3. 1H NMR (270MHz, CDCl3) δ 1.35
(s, 12H), 4.45 (s, 2H), 7.35 (d, 2H, J=8.1), 7.75 (d, 2H,
J=8.1); 13 C NMR (67.8MHz, CDCl3) δ 24.8, 33.3, 76.5,
Funding
The author(s) disclosed receipt of the following financial support for
the research, authorship and/or publication of this article: Financial
support from EPSRC under Grant GR/F 20937 is gratefully acknowl-
edged, and Dr. Ballantine and B. Stein of the EPSRC MS Service
83.88, 128.3, 135.2, 140.6; LRMS (EIMS) m/z (%) 432 ((2 Centre, Swansea, for EI/CI, FAB and ESIMS measurements.

D’Silva
5
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23. Higgins SJ. Chem Soc Rev 1997; 26: 247.
24. Schalkhammer T, Mann-Buxbaum E, Pittner F, et al. Sens
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ORCID iD
Claudius D’Silva
https://orcid.org/0000-0002-0213-9503
Supplemental material
The 1H, 13C NMR, and microanalysis are available online.
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