Full Papers
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and wet acetonitrile (0.36 mg, 19,99 μmol, 0.1 m, 2 eq.) were added
and shaken for 1 min. Finally, periodic H NMR spectra were
recorded with a total duration of 14 h. The conversion was
determined by the ratio of starting material 21 and the product 22.
Hereto the relative integral of the methyl group of trans-β-
crotonophenone (21, dd, 1.99 ppm) was set to 1. The conversion is
equal 100%, divided through the sum of starting material 21 and
product 22 (signal of the methyl group at 1.46 ppm (d) and
multiplied by the integral of the product signal. Alternatively, the
signal of the CH bond (s, 3.78 ppm) in the product 22 was
compared with the hydrogen in β-position (m, 6.55 ppm) of the
indole (20).
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to an NMR tube, sealed and vigorously shaken for one minute.
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Finally, periodic H NMR spectra were recorded with a total duration
of 10 h. The conversion was determined by the ratio of starting
material 10 and the product 11. Hereto, the relative integral of a
significant singlet of benzhydryl bromide (6.45 ppm) was set to 1.
The conversion is equal to 100%, divided through the sum of
starting material 10 and product 11 (significant doublet at
6.30 ppm) and multiplied with the integral of the product signal.
Activation of benzhydryl bromide (10) in Friedel-Crafts
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alkylation reaction with 1,3,5-trimethoxy benzene (12): The
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reaction was performed in chloroform. For the reaction, Cs CO
Catalytic nitro-Michael addition reaction of 5-methoxyindole (23)
and trans-β-nitrostyrene (24): The reaction was performed in
methylene chloride. In each case, 200 μl of the respective stock
solution of the halogen bond catalyst (3.74 μmol, 0.04 m, 0.2 eq.,
88.0 μl), 5-methoxyindole (23; 8.25 mg, 56.1 μmol, 0.28 m, 3 eq.)
and trans-β-nitrostyrene (24; 2.79 mg, 18.7 μmol, 0.09 m, 1 eq.)
were added to an NMR tube, sealed and shaken for 1 minute.
Finally, periodic H NMR spectra were recorded with a total duration
of 48 h. The conversion was determined by the ratio of the product
25 against a tetraethyl silyl (TES) standard. Hereto the relative
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(3.26 mg, 9.99 μmol, 1 eq.) and in each case 200 μl of the respective
stock solution of the halogen bond activator (9.99 μmol, 0.05 m,
1 eq.), benzhydryl bromide (10; 2.47 mg, 9.99 μmol, 0.05 m, 1 eq.)
and 1,3,5-trimethoxy benzene (12; 1.68 mg, 9.99 μmol, 0.05 m,
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eq.) were added to an NMR tube, sealed, shaken and sonicated
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for 2 minutes. Finally, periodic H NMR spectra were recorded with
a total duration of 8 h. The conversion was determined by the ratio
of starting material 12 and the product 13. Hereto the relative
integral of methoxy groups of 1,3,5-trimethoxy benzene (12) (s,
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.77 ppm) was set as 1. The conversion is equal 100%, divided
integral of C group of TES (0.38 eq., q, 0.55 ppm) was set as 1.
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through the sum of starting material 12 and product 13 (signals for
the two methoxy groups at 3.80 ppm (s) and 3.58 ppm (s)) and
multiplied with the integral of the product signals.
Integration of the newly formed CH - and CH-bond (m, 5.04 ppm)
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of product 25 and multiplication with 100% directly gave the
conversion.
Catalytic activation of 1-chloroisochroman (14): The reaction was
performed in non-deuterated THF. To an oven dried Schlenk finger,
equipped with a stirring bar and rubber septum under argon Conflict of Interest
atmosphere were added the respective halogen bond catalyst
(0.5 μmol, 0.005 eq.) and 900 μl dry THF. The mixture was cooled to
The authors declare no conflict of interest.
À 78°C and subsequently, 100 μl of a freshly prepared 1 m stock
solution of 1-chloroisochroman (14) in THF were added. The
mixture was stirred for 20 min and ketene silyl acetal 15 (28.26 mg,
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50 μmol, 32.9 μl, 1.5 eq.) was added and the mixture was stirred at Acknowledgements
À 78°C for 6 h. Next, the reaction mixture was quenched through
addition of 200 μl of a 0.5 m methanolate solution in methanol
(100 μmol, 1 eq.), filtered through a plug of silica with diethyl ether
and was finally purified via column chromatography (penta-
ne:diethyl ether 9:1). Product compound 16 was obtained as
colourless oily compound. The purity of the isolated compound
This project has received funding from the European Research
Council (ERC) under the European Union’s Horizon 2020 research
and innovation programme (638337).
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was proven by TLC and H NMR measurements.
Keywords: halogen bonding · Lewis acids · organocatalysis ·
anion recognition · solution
Catalytic Diels-Alder reaction of cyclopentadiene (17) and methyl
vinyl ketone (18): The reaction was performed in methylene
chloride. Cyclopentadiene (17) was freshly prepared from
dicyclopentadiene through thermal cracking at 250°C. In each case,
[2] M. Breugst, D. von der Heiden, J. Schmauck, Synthesis 2017, 49, 3224–
3236.
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00 μl of the respective stock solution of the halogen bond catalyst
(0.03 μmol, 0.015 m, 0.005 eq.), cyclopentadiene (17; 10.24 mg,
155 μmol, 0.78 m, 10 eq.) and methyl vinyl ketone (18; 1.09 mg,
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5.5 mmol, 0.078 m, 1 eq.) were added to an NMR tube, sealed and
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shaken for 1 min. Finally, periodic H NMR spectra were recorded
with a total duration of 1 h. The conversion was determined by the
ratio of starting material 18 and the product 19. Hereto the relative
integral of methyl group of methyl vinyl ketone (18; s, 2.25 ppm)
was set as 1. The conversion is equal 100%, divided through the
sum of starting material 18 and product 19 (signal of the methyl
group of the endo- and exo- product at 2.09 ppm (s) and at
[
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.18 ppm (s) with a ratio of approximately 10:1) and multiplied by
the sum of integrals of the product signals.
[
Catalytic Michael addition reaction of indole (20) and trans-β-
crotonophenone (21): The reaction was performed in methylene
chloride. In each case, 200 μl of the respective stock solution of the
halogen bond catalyst (12 μmol, 0.06 m, 0.2 eq.), indole (20;
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.03 mg, 60 μmol, 0.3 m, 1 eq.) and trans-β-crotonophenone (21;
8.77 mg, 60 μmol, 0.3 m, 1 eq.) were added to an NMR tube, sealed
ChemistryOpen 2020, 9, 214–224
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