Heteromultifunctional Oxazolones as Versatile Linkers for Click Chemistry Reactions

Article abstract of DOI:10.1002/ejoc.201901350

New oxazolone-based heteromultifunctional linkers were synthesized using a zinc-mediated double functionalization of nitriles as the key step. The orthogonality of the functional groups displayed by this original scaffold was demonstrated by conducting se

Full text of DOI:10.1002/ejoc.201901350

A Journal of
Accepted Article
Title: Heteromultifunctional oxazolones as versatile linkers for click
chemistry reactions
Authors: Mathilde Pantin, Julien Caillé, Fabien Boeda, Laurent
Fontaine, Morwenna Soizic Marie Pearson-Long, and Philippe
Bertus
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10.1002/ejoc.201901350
European Journal of Organic Chemistry
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Heteromultifunctional oxazolones as versatile linkers for click
chemistry reactions
Mathilde Pantin, [a] Julien Caillé, [a] Fabien Boeda, [a] Laurent Fontaine, [a] Morwenna S. M. Pearson-
Long,*[a] and Philippe Bertus*[a]
Abstract: New oxazolone-based heteromultifunctional linkers were
synthesized using a zinc-mediated double functionalization of nitriles
as the key step. The orthogonality of the functional groups displayed
by this original scaffold was demonstrated by conducting sequential
or simultaneous multi-component reactions with amines (oxazolone
ring opening), thiols (thiol-ene radical reaction) and azides (Cu-
catalyzed azide-alkyne coupling), in respect to the concept of click
chemistry.
avoiding time-consuming activation and/or deprotection steps
and/or the formation of byproducts remains highly desirable.
Introduction
Heteromultifunctional coupling reagents are molecules of
great importance for bioconjugation, diagnosis, therapy and
layer functionalization.1,2 These chemical tools should
display different functionalities able to link specific partners
orthogonally by a sequential combination of chemoselective
ligations.3,4 Among all these bioorthogonal reactions,1c the
most widely used is the Sharpless copper-catalyzed azide-
alkyne cycloaddition (CuAAC).5 Nevertheless, the use of
copper salts remains a main drawback, especially for bio-
related applications.6 In order to overcome this limitation the
Cu-free strain-promoted azide-alkyne cycloaddition was
introduced.7 Several other reactions are also used,8 such as
tetrazine-based inverse-electron demand Diels Alder
reactions with strained alkenes,9 addition to maleimide
derivatives,10 nucleophilic addition of amines onto activated
Figure 1. Examples of heteromultifunctional linkers 1-4 and the structure of
the linker 5b, subject of this work.
In this context, we were interested in developing new
linkers able to react in underexplored coupling reactions,
namely the amine-mediated ring opening of 1,3-oxazol-
5(4H)-ones (also named azlactones),17 and the thiol-ene
radical addition.18,19 These two reactions present the benefit
to directly link amine and thiol moieties respectively, without
formation of any byproduct (click chemistry).20 Indeed, the
esters
(N-hydroxysuccinimidyl
(NHS),
pentafluorophenyl,...),11 the photocrosslinking involving
benzophenone partners,12 and the transition metal-
catalyzed cross coupling reactions (Suzuki,13 Glaser
reactions,14...).
Among the heterobifunctional linkers
oxazolone functionality has emerged as
a powerful
reported in the literature, the most popular ones display
amine- and thiol-reactive functions particularly useful to
directly link biomolecules such as proteins and antibodies.15
The introduction of an additional functionality on the linker
offers new perspectives of coupling, as reported these last few
years with the selected examples of polyfunctional linkers 1-4
presented on figure 1.16 Nevertheless, the direct orthogonal
coupling of several molecules with multifunctional linkers
chemical tool due to its high reactivity towards primary and
secondary amines without generating byproducts neither
requiring any catalyst. This reaction, proceeding with
complete atom economy, can be conducted in a broad
range of organic solvents as well as in aqueous solution at
room temperature. Additionally, the azlactone group is
relatively stable to hydrolysis, a substantial advantage
compared to NHS ester derivatives.
In this work, we present the elaboration of new linkers
displaying both oxazolone and alkene moieties, and
possibly a third orthogonal clickable functionality (alkyne),
such as in the multifunctional linker 5b (Fig. 1), with the
challenge to increase the functional diversity and multiplicity
without affecting the highly reactive oxazolone function.21 In
[a]
Dr. Pantin, Dr. Caillé, Dr. Boeda, Prof. Fontaine, Dr. Pearson-Long,
and Prof. Bertus
Institut des Molécules et Matériaux du Mans,
IMMM UMR 6283 CNRS - Le Mans Université,
Avenue Olivier Messiaen, 72085 Le Mans Cedex 09, France
morwenna.pearson@univ-lemans.fr
philippe.bertus@univ-lemans.fr
http://immm.univ-lemans.fr/fr/index.html
contrast
to
succinimidyl
4-(N-maleimidomethyl)-
cyclohexane-1-carboxylate (SMCC), an amine-to-sulfhydryl
linker that contains NHS-ester and maleimide reactive
Supporting information for this is given via a link at the end of the
document.
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10.1002/ejoc.201901350
European Journal of Organic Chemistry
FULL PAPER
groups frequently used for the preparation of antibody-drug
conjugates (ADCs) and other functional conjugates,22 the
reported bis-allyl-functionalized linkers of this work can
potentially link two molecules of thiol, thus increasing the
loading in active compound of the final bioconjugate.
Therefore, these linkers would be able to graft up to four
partners without byproduct release, nor activation step. The
strategy to access these valuable compounds is based on
our
recently
developed
straightforward
double
functionalization of nitriles.23
Scheme 2. Reactivity of oxazolone 5a towards thiol-ene reaction. DMPA
= 2,2-dimethoxy-2-phenylacetophenone. Yields were calculated after
Results and Discussion
purification of the crude mixture, and separation of
9 and 10.
As depicted in scheme 1, the reaction of allylzinc reagent
on acylcyanohydrins 6a23c and 6b, easily prepared from the
corresponding carboxylic acids, results in the very selective
Interestingly, the outcome of the reaction depends on the
experimental conditions. When the reaction was carried out
in low concentration (0.02 M in DMF), the spirocyclic
formation of the corresponding hydroxyamides
7, in
quantitative yields. These compounds were efficiently
converted into the corresponding acids 8a and 8b after a
two-step oxidation sequence. The trimethylsilyl group of 8b
compound
9 resulting from the incorporation of only one
thiol was obtained as the unique or major product, whatever
the quantity of mercaptan added. The formation of this
compound is easily explained by a first addition of the
benzyl thiyl radical onto one double bond, followed by a 5-
exo-trig subsequent cyclization reaction with the remaining
double bond. Performing the reaction with 2 equivalents of
thiol in DMF or THF in more concentrated conditions, favors
the formation of 10, and a complete double thiol-ene
reaction was observed when 10 equivalents of thiol were
added in THF. Finally, the best conditions were found by
conducting the reaction in the presence of an excess of the
thiol partner and without any solvent, to provide 10 in 95%
yield. It should be underlined that under these conditions,
the oxazolone moiety remains unaffected. In contrast, as
expected, the addition of benzylamine to 5a occurs
selectively and quantitatively in DMSO (40 °C, 24 h),
leading to the amide 11 as shown in Scheme 3. Whereas
the oxazolone 5a remains unreactive towards aniline
(aromatic amine), the addition was successfully performed
was then removed, and the oxazolone heterocycles 5a-b
were finally obtained via a cyclization reaction involving
ethyl chloroformate reagent. In this procedure, the
oxazolones were thus synthesized from the starting nitriles
without time-consuming purification of the intermediates,
and in excellent overall yields.
with an aminoacid derivative (methyl alaninate).25
A
subsequent thiol-ene reaction under the above optimized
conditions afforded 12 or 13, according to the chosen
reaction conditions. These compounds are also accessible
Scheme 1. Synthesis of oxazolones 5a-b. (i) allyl bromide, activated zinc
powder, THF, rt; (ii) IBX, DMSO, 50 °C; (iii) NaH2PO4, NaClO2, H2O2, MeCN,
rt; (iv) For 5a: ethyl chloroformate, Et3N, acetone, rt; (v) For 5b: a) K2CO3,
MeOH/THF, rt, b) ethyl chloroformate, Et3N, acetone, rt.
by aminolysis of thiol-ene products
9 and 10, which confirm
the orthogonality of the oxazolone and allyl moieties.
The orthogonal reactivity of the oxazolone and allyl
moieties
toward
aminolysis
and
radical
alkene
hydrothiolation was first investigated with the model
substrate 5a. The thiol-ene reaction was performed with
benzylmercaptan under conventional conditions (DMPA as
photoinitiator, 365 nm UV irradiation, Scheme 2).24
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10.1002/ejoc.201901350
European Journal of Organic Chemistry
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Alternatively, the CuAAC reaction involving substrate 5b
and benzyl azide as coupling partner allowed the formation
of triazole 16 in 97% yield and the following aminolysis with
benzylamine afforded compound 15 in 96% yield.
Interestingly, the grafting of the two partners has also been
achieved simultaneously on 5b in a “one-pot” procedure to
efficiently provide compound 15 which was isolated in 95%
yield. This result clearly highlights the orthogonal chemical
reactivity of the alkyne vs oxazolone core.
In
a second time, aminolysis and hydrothiolation
reactions have been investigated. The thiol-ene reaction
between benzyl mercaptan and diallyl oxazolone 16 was
performed using DMPA as photoinitiator. After one hour of
reaction under UV irradiation, bis-thioether 17 was isolated
in 91% yield. The ring-opening of the oxazolone core was
then performed upon nucleophilic addition of benzylamine
to furnish compound 18 in 96% yield. The reversed
sequence has been also studied. Indeed, after aminolysis
of 16 in 96% yield, the product 15 was subjected to
hydrothiolation reaction conditions and the expected
compound 18 was obtained with a high yield of 96%.
Importantly, the CuAAC reaction must be performed before
the thiol-ene reaction, otherwise some concomitant
hydrothiolation of the alkyne function occurred and a
Scheme 3. Reactivity of oxazolone 5a towards thiol-ene and aminolysis
reactions. (i) BnNH2, DMSO, 40 °C; (ii) BnSH (1 equiv), DMF (0.02 M),
DMPA (10 mol%), UV irradiation (365 nm), rt; (iii) BnSH (10 equiv),
DMPA (10 mol%), UV irradiation (365 nm), rt.
The reactivity of oxazolone 5b, displaying a terminal
alkyne function, was then studied in order to propose an
additional click transformation, and thus to validate the
feasibility of the sequential anchoring of different partners
on the linker. First of all, aminolysis and CuAAC reactions
have been investigated (Scheme 4). The nucleophilic
addition of benzylamine onto oxazolone 5b proceeded
efficiently to provide diamide 14 in 97% yield and the
subsequent copper-catalyzed Huisgen cycloaddition with
benzyl azide furnished compound 15 quantitatively.
mixture
of
addition
products
is
formed.
Scheme 4. Reactivity of oxazolone 5b towards aminolysis and CuAAC reactions.
These results in hand, we focused our attention on a
method to anchor three different partners on oxazolone 5b
without any purification step (Scheme 5). For that purpose,
alkynyl diallyloxazolone 5b was mixed with benzyl azide,
PMEDTA, copper bromide and benzylamine in DMF. After 16h
of reaction at 40 °C, the crude mixture (obtained after addition of
water followed by an extraction with AcOEt) was directly treated
with DMPA and benzyl mercaptan. After 1h of UV irradiation, the
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10.1002/ejoc.201901350
European Journal of Organic Chemistry
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ATR unit. High resolution mass spectra were recorded on a Waters
Micromass GCT Premier spectrometer.
targeted compound 18 was obtained in 85% yield. This result
validates our goal, which was to realize a three-click reactions
sequence without byproduct release. It is worth mentioning that
a classical “one-pot” methodology did not proceed well since the
presence of DMF was detrimental to hydrothiolation reaction.
N-(4-(Hydroxymethyl)hepta-1,6-dien-4-yl)benzamide (7a):23a To
a
suspension of zinc powder (12.2 g, 186.3 mmol) in THF (200 mL) was
added allylbromide (16.1 mL, 186.3 mmol). The mixture was refluxed for
2 minutes, and cooled down to rt. The organozinc bromide solution was
then added dropwise over 5 minutes, to a solution of the cyanomethyl
benzoate 6a (10.0 g, 62.1 mmol) in THF (100 mL) cooled to 0 °C. The
mixture was stirred 5 minutes at 0 °C then a 1M aqueous HCl solution
(150 mL) was added. The aqueous layer was extracted with EtOAc (2 x
100 mL) then the combined organic layers were successively washed
with a 2M aqueous NaOH solution and brine, dried over anhydrous
MgSO4 and filtrated. The solvents were removed in vacuo to afford the
hydroxyamide 7a (15.2 g, quantitative yield) as a colorless oil. 1H NMR
(CDCl3, 200 MHz): δ 7.73-7.65 (m, 2H, HAr), 7.55-7.40 (m, 3H, HAr), 6.38
(br s, 1H, NH), 5.92 (m, 2H, CH=CH2), 5.31-5.21 (m, 4H, CH=CH2), 5.08
(t, J = 6.5 Hz, 1H, OH), 3.78 (d, J = 6.5 Hz, 2H, CH2OH), 2.66 (ddt, J =
Scheme 5. Sequential “one-pot” method leading directly to 18
.
13.9, 6.6, 1.2 Hz, 2H, CH2), 2.38 (ddt, J = 13.9, 8.4, 1.0 Hz, 2H, CH2). 13
C
NMR (CDCl3, 50 MHz): δ 168.4 (C=O), 134.8 (CAr), 133.1 (2 CH=CH2),
131.9 (CAr), 128.9 (2 CAr), 127.0 (2 CAr), 120.1 (2 CH=CH2), 68.3
(CH2OH), 60.4 (C), 39.1 (2 CH2).
Conclusions
In summary, we developed the preparation of functionalized
oxazolones relying on a high yielding four- or five-step synthetic
sequence. One of these new heteromultifunctional linkers (5b),
displaying three functional groups able to undergo orthogonal
modifications, was successfully subjected to the crosslinking of
various model partners, with the only requirement to perform the
CuAAC reaction previous to the thiol-ene reaction. Ultimately, a
sequential “one-pot” method to anchor selectively these three
model molecules (azide, amine and thiol) has been performed.
These encouraging results pave the way for further studies
dealing with the use of our platform in bioconjugation or surface
functionalization challenges.
2-Benzamido-2-allylpent-4-enoic acid (8a): IBX (18.26 g, 65.2 mmol)
was added to a solution of amino alcohol 7a (8.0 g, 32.6 mmol) in DMSO
(60 mL) at rt. The reaction mixture was then stirred at 50 °C for 16 h.
EtOAc was added and the crude mixture was filtered through a pad of
Celite®. The filtrate was washed with brine and dried over anhydrous
Na2SO4. Concentration in vacuo afforded N-(4-formylhept-1,6-dien-4-
1
yl)benzamide as a yellow oil (7.93 g, quantitative yield). H NMR (CDCl3,
400 MHz): δ (ppm) 9.46 (s, 1H, CHO), 7.78-7.76 (m, 2H, HAr), 7.55-7.50
(m, 1H, HAr), 7.47-7.43 (m, 2H, HAr), 6.78 (br s, 1H, NH), 5.65 (dddd, J =
17.0, 10.1, 7.4, 7.2 Hz, 2H, CH=CH2), 5.18-5.12 (m, 4H, CH=CH2), 3.10
(dd, J = 14.3, 7.2 Hz, 2H, CH2), 2.66 (dd, J = 14.3, 7.4 Hz, 2H, CH2). 13
C
NMR (CDCl3, 100 MHz): δ (ppm) 199.9 (CHO), 166.8 (C=O), 134.2 (CAr),
131.8 (CAr), 131.3 (2 CH=CH2), 128.7 (2 CAr), 126.9 (2 CAr), 120.1
(2 CH=CH2), 65.8 (C), 37.1 (2 CH2). IR (neat): ν = 3075, 2926, 1721,
1639, 1525, 1276 cm-1. HRMS (ESI+): m/z (M+Na+) calcd for
C15H17NO2Na: 266.1152, found: 266.1151.
Experimental Section
Experiments involving organometallic reagents and thiol-ene reactions
were carried out under N2 atmosphere. THF and CH2Cl2 were purified by
passing through neutral alumina columns under nitrogen. DMSO and
DMF were distilled under nitrogen before use. The zinc source consists
in an activated zinc powder prepared as followed: to an aqueous 1M
solution of HCl (100 mL) was added zinc dust (5 g). The resulting
suspension was stirred for 30 minutes at rt then filtered and washed
successively with water (twice), EtOH and Et2O. The activated zinc
powder was dried under vacuum over at least 10 h. A shining grey
appearance of the metal should be observed during this last stage. The
activated zinc powder could be stored under argon for several months at
rt. IBX was prepared according to the protocol described by the group of
B. Schmidt.21 Analytical TLC were performed on Alugram SIL G/UV254
silica gel sheets (Macherey-Nagel) by using UV revelation or potassium
permanganate solution (KMnO4). Column chromatography was carried
out using silica gel 60 (0.040-0.063 mm) from Merck. Melting points were
To a solution of the aldehyde (32.6 mmol) in MeCN (250 mL) cooled to
0 °C were successively added sodium phosphate monobasic dihydrate
(10.2 g, 65.2 mmol) in water (100 mL), H2O2 (30% w/w in H2O, 18.5 mL,
163 mmol) and sodium chlorite (4.42 g, 48.9 mmol). The reaction mixture
was stirred at rt and the progress of the reaction was monitored by TLC.
Sodium thiosulfate (5.15 g, 32.6 mmol) was then added and the reaction
mixture was stirred for 1 h. The solvent was removed in vacuo, then
EtOAc (200 mL) and sat. aq. NaHCO3 (200 mL) were added to the
residue. The layers were separated and the organic phase was washed
with sat. aq. NaHCO3 (2 x 100 mL). The combined aqueous layers were
acidified by adding conc. HCl and extracted with EtOAc (3 x 100 mL).
After drying over MgSO4, the combined organic layers were concentrated
in vacuo to provide the pure N-benzoyl-protected amino acid 8a (6.55 g,
80% yield) as a pale yellow solid; mp = 134-136 °C. 1H NMR (CDCl3, 200
MHz): δ (ppm) 8.95 (bs, COOH), 7.78-7.72 (m, 2H, HAr), 7.59-7.38 (m,
3H, HAr), 7.11 (br s, 1H, NH), 5.69 (dddd, J = 17.1, 10.2, 7.7, 7.2 Hz, 2H,
CH=CH2), 5.20-5.05 (m, 4H, CH=CH2), 3.31 (dd, J = 14.0, 7.7 Hz, 2H,
CH2), 2.70 (dd, J = 14.0, 7.2 Hz, 2H, CH2). 13C NMR (CDCl3, 100 MHz): δ
(ppm) 176.2 (COOH), 167.5 (C=O), 134.5 (CAr), 132.0 (2 CH=CH2),
131.8 (CAr), 128.7 (2 CAr), 127.0 (2 CAr), 119.7 (2 CH=CH2), 64.4 (C),
39.1 (2 CH2). IR (neat): ν = 3342, 3075, 2982, 2926, 2251, 1727, 1639,
1522, 1276 cm-1. HRMS (ESI+): m/z (M+Na+) calcd for C15H17NO3Na:
282.1101, found: 282.1097.
determined with
a Büchi B-540 melting point apparatus and are
uncorrected. 1H and 13C NMR spectra were recorded on a Bruker DPX-
200 or Bruker AC-400 spectrometer. Chemical shifts (δ) are expressed in
ppm units, relative to the residual solvent peak. Coupling constants are
given in Hz. The multiplicities are reported as follows: singlet (s), doublet
(d), triplet (t), quadruplet (q), pentuplet (p), appearing pentuplet (app p),
multiplet (m), and broad signal (br s). IR spectra were obtained on a
Perkin Elmer Spectrum One spectrometer on a single-reflection diamond
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10.1002/ejoc.201901350
European Journal of Organic Chemistry
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4,4-Diallyl-2-phenyloxazol-5(4H)-one (5a):27 Et3N (2.75 mL, 20.4 mmol)
and ethyl chloroformate (1.29 mL, 13.6 mmol) were added to a solution
of acid 8a (3.52 g, 13.6 mmol) in acetone (100 mL) at 0 °C. After stirring
at rt for 3 h, the reaction mixture was filtered through a pad of silicagel
then concentrated in vacuo to afford the oxazolone 5a (3.28 g,
quantitative yield) as a orange oil. 1H NMR (CDCl3, 200 MHz): δ (ppm)
8.02-7.98 (m, 2H, HAr), 7.60-7.52 (m, 1H, HAr), 7.51-7.42 (m, 2H, HAr),
5.66 (dddd, J = 17.0, 10.0, 8.0, 6.8 Hz, 2H, CH=CH2), 5.23-5.06 (m, 4H,
CH=CH2), 2.68 (dd, J = 13.8, 6.8 Hz, 2H, CH2), 2.58 (dd, J = 13.8, 8.0 Hz,
2H, CH2). 13C NMR (CDCl3, 100 MHz): δ (ppm) 179.2 (C=O), 160.1
(C=N), 132.8 (CAr), 130.8 (2 CAr), 128.8 (2 CAr), 128.0 (2 CH=CH2), 125.9
(CAr), 120.6 (2 CH=CH2), 73.8 (C), 41.1 (2 CH2). HRMS (ESI+): m/z
(M+Na+) calcd for C15H15NO2Na: 264.0995, found: 264.1002.
2H, CH2), 0.25 (s, 9H, CH3). 13C NMR (CDCl3, 100 MHz): δ (ppm) 199.9
(CHO), 166.2 (C=O), 133.7 (CAr), 132.3 (2 CAr), 131.2 (2 CH=CH2), 126.9
(CAr), 126.9 (2 CAr), 120.2 (2 CH=CH2), 104.0 (C≡C), 97.4 (C≡C),
66.0 (C), 37.1 (2 CH2), 0.0 (3 CH3). IR (neat): ν = 3295, 2164, 1733, 1629,
1525 cm-1. HRMS (ESI+): m/z (M+Na+) calcd for C20H35NNaO2Si:
362.1547,
found:
362.1539.
2-Allyl-2-(4-
((trimethylsilyl)ethynyl)benzamido)-pent-4-enoic acid (8b): 1H NMR
(CDCl3, 400 MHz): δ (ppm) 7.67 (d, J = 8.4 Hz, 2H, HAr), 7.50 (d, J = 8.4
Hz, 2H, HAr), 7.00 (s, 1H, NH), 5.68 (dddd, J = 17.1, 9.9, 7.3, 7.3 Hz, 2H,
CH=CH2), 5.21-5.06 (m, 4H, CH=CH2), 3.29 (dd, J = 13.9, 7.6 Hz, 2H,
CH2), 2.69 (dd, J = 14.0, 7.2 Hz, 2H, CH2), 0.25 (s, 9H, CH3). 13C NMR
(CDCl3, 100 MHz): δ (ppm) 177.6 (COOH), 166.5 (C=O), 134.2 (CAr),
132.3 (2 CAr), 131.9 (2 CH=CH2), 126.9 (3 CAr), 119.9 (2 CH=CH2), 104.1
(C≡C), 97.3 (C≡C), 64.6 (C), 39.2 (2 CH2), 0.0 (3 CH3). IR (neat): ν =
2959, 2162, 1709, 1639, 1525, 1493, 1251 cm-1. HRMS (ESI+): m/z
(M+Na+) calcd for C20H25NNaO3Si: 378.1496, found: 378.1492.
Cyanomethyl 4-((trimethylsilyl)ethynyl)benzoate (6b): To a solution of
4-iodobenzoic acid (2.48 g, 10 mmol) in dry triethylamine (20 mL) and
THF (40 mL) under argon were successively added Pd(PPh3)Cl2 (421 mg,
0.6 mmol), CuI (191 mg, 1 mmol) and trimethylsilylacetylene (2.40 mL,
17 mmol). Stirring was maintained for 18 h at rt and the reaction mixture
4,4-Diallyl-2-(4-ethynylphenyl)oxazol-5(4H)-one (5b): To a solution of
acid 8b (1.0 g, 2.81 mmol) in a 2:1 mixture of MeOH and THF (15 mL)
was added K2CO3 (777 mg, 5.62 mmol). The mixture was stirred at rt for
2 h, and then concentrated in vacuo. The residue was taken up in water
(20 mL) and EtOAc (20 mL) and the pH was adjusted to pH 1 by adding
conc. HCl. The phases were separated and the aqueous fraction was
extracted with EtOAc (2 x 15 mL). The combined organic layers were
washed with brine, dried over MgSO4, filtered and the solvent was
removed in vacuo to afford the pure corresponding 4-
(ethynyl)benzamido-2-allylpent-4-enoic acid (795 mg, quantitative yield,
yellow oil) without any further purification. 1H NMR (DMSO-d6, 400 MHz):
δ (ppm) 12.59 (br s, 1H, COOH), 8.22 (br s, 1H, NH), 7.81 (d, J = 8.3 Hz,
2H, HAr), 7.57 (d, J = 8.3 Hz, 2H, HAr), 5.70 (dddd, J = 16.2, 11.0, 7.4, 7.2
Hz, 2H, CH=CH2), 5.09-5.05 (m, 4H, CH2=CH), 4.36 (C≡CH), 2.73 (dd, J
= 14.1, 7.2 Hz, 2H, CH2), 2.61 (dd, J = 14.1, 7.4 Hz, CH2). 13C NMR
(DMSO-d6, 100 MHz): δ (ppm) 173.3 (COOH), 165.0 (C=O), 134.4 (CAr),
132.8 (2 CH=CH2), 131.6 (2 CAr), 127.6 (2 CAr), 124.5 (CAr), 118.7
(2 CH=CH2), 82.9 and 82.8 (C≡CH and C≡CH), 61.4 (C), 37.5 (2 CH2).
HRMS (ESI+): m/z (M+Na+) calcd for C17H17NO3Na: 306.1106, found:
306.1105.
was filtered through
a
pad of Celite®. The organic filtrate was
successively washed with 1M aq. HCl solution (3 x 100 mL), water (150
mL) and brine (2 x 100 mL). After drying over MgSO4, the organic fraction
was filtered and concentrated in vacuo to give the crude 4-
((trimethylsilyl)ethynyl)benzoic acid, which was directly dissolved in
CH2Cl2 (20 mL). Triethylamine (2.7 mL, 20 mmol) and chloroacetonitrile
(1.0 mL, 15 mmol) were added and the resulting mixture was stirred for
48 h at rt. The reaction mixture was concentrated in vacuo and the
residue was taken up with water (10 mL) and CH2Cl2 (10 mL). The layers
were separated and the aqueous phase was extracted with CH2Cl2
(2 x 10 mL). The combined organic layers were washed with sat. aq.
NaHCO3, dried over MgSO4, filtered and the solvent was removed in
vacuo.
Purification
by
flash
chromatography
on
silicagel
(Cyclohexane/EtOAc 98:2, then 9:1) provided the acylcyanohydrin 6b
(1.93g, 75% yield) as an orange solid; mp = 50-52 °C. 1H NMR (CDCl3,
400 MHz): δ (ppm) 7.98 (m, 2H, HAr), 7.55 (m, 2H, HAr), 4.96 (s, 2H, CH2),
0.27 (s, 9H, CH3). 13C NMR (CDCl3, 100 MHz): δ (ppm) 164.6 (C=O),
132.3 (CAr), 130.0 (2 CAr), 129.4 (2 CAr), 127.5 (CAr), 114.6 (CN), 103.8
(C≡C), 99.2 (C≡C), 49.2 (CH2), 0.0 (3 CH3). IR (neat): ν = 3097, 2959,
2903, 2113, 1737, 1603, 1410, 1253, 1097 cm-1. HRMS (ESI+): m/z
(M+Na+) calcd for C14H15NO2SiNa: 280.0770, found: 280.0766.
The crude acid was then dissolved in acetone (10 mL) and the solution
was cooled to 0 °C. Et3N (0.57 mL, 4.22 mmol) and ethyl chloroformate
(0.27 mL, 2.81 mmol) were added and the mixture was stirred at rt for 3 h.
The reaction mixture was filtered through a pad of silicagel then
concentrated in vacuo to afford the oxazolone 5b (731 mg, 98% yield) as
N-4-((Hydroxymethyl)hepta-1,6-dien-4-yl)-4-((trimethylsilyl)ethynyl)-
benzamide (7b): Same procedure as for 7a. A pale yellow solid is
obtained starting from 6b (1.5 g, 5.80 mmol), no purification was required
1
a yellow oil. H NMR (CDCl3, 400 MHz): δ (ppm) 7.98-7.91 (m, 2H, HAr),
1
(2.0 g, quantitative yield); mp = 88-90 °C. H NMR (CDCl3, 400 MHz): δ
7.62-7.56 (m, 2H, HAr), 5.63 (dddd, J = 17.0, 9.9, 7.7, 6.9 Hz, 2H,
CH=CH2), 5.22-5.08 (m, 4H, CH=CH2), 3.25 (s, 1H, C≡CH), 2.67 (dd, J =
13.7, 6.9 Hz, 2H, CH2), 2.58 (dd, J = 13.7, 7.7 Hz, 2H, CH2). 13C NMR
(CDCl3, 100 MHz): δ (ppm) 179.0 (C=O), 159.6 (C=N), 132.5 (2 CAr),
130.6 (2 CH=CH2), 127.9 (2 CAr), 126.7 (CAr), 125.9 (CAr), 120.7 (2
CH=CH2), 82.8 (C≡CH), 80.5 (C≡CH), 73.9 (C), 41.1 (2 CH2). IR (neat): ν
= 3290, 2925, 1820, 1722, 1644, 1525, 1495, 1220 cm-1. HRMS (ESI+):
m/z (M+Na+) calcd for C17H15NNaO2: 288.0995, found: 288.0987.
(ppm) 7.63 (d, J = 8.4 Hz, 2H, HAr), 7.50 (d, J = 8.4 Hz, 2H, HAr), 6.35 (br
s, 1H, NH), 5.90 (dddd, J = 16.3, 11.0, 8.6, 6.7 Hz, 2H, CH=CH2), 5.25-
5.18 (m, 4H, CH=CH2), 4.92 (br s, 1H, OH), 3.76 (s, 2H, CH2OH), 2.64
(dd, J = 13.9, 6.7 Hz, 2H, CH2), 2.37 (dd, J = 13.9, 8.6 Hz, 2H, CH2), 0.25
(s, 9H, CH3). 13C NMR (CDCl3, 100 MHz): δ (ppm) 167.6 (C=O), 134.3
(CAr), 133.0 (2 CH=CH2), 132.3 (2 CAr), 126.9 (CAr), 126.8 (2 CAr), 120.1
(2 CH=CH2), 104.0 (C≡C), 97.5 (C≡C), 68.1 (CH2OH), 60.4 (C), 39.1 (2
CH2), -0.02 (3 CH3). IR (neat): ν = 3294, 3082, 2959, 2925, 2903, 2873,
2162, 1726, 1637, 1547, 1465, 1439, 1328, 1253, 1074 cm-1. HRMS (CI+,
NH3/CH4): m/z (M+H+) calcd for C20H28NO2Si: 342.1889, found: 342.1889.
7-((Benzylthio)methyl)-8-methyl-2-phenyl-3-oxa-1-aza-spiro[4.4]non-
1-en-4-one (9): DMPA (8.8 mg, 33 µmol) and benzylmercaptan (40 µL,
0.33 mmol) were added to a solution of 5a (80 mg, 0.33 mmol) in
degassed DMF (17 mL) at rt. The reaction mixture was stirred at rt under
UV irradiation (365 nm) for 1 h then diluted with EtOAc and brine. The
phases were separated and the aqueous fraction was extracted with
EtOAc (2 x 10 mL). The combined organic layers were dried over
anhydrous Na2SO4, filtered and concentrated in vacuo. Purification by
flash chromatography (Cyclohexane/Et2O 95:5) provided the spiro
compound 9 (102 mg, 85% yield) as a 70:30 mixture of diastereoisomers,
which were separated by flash chromatography and isolated as colorless
2-Allyl-2-(4-((trimethylsilyl)ethynyl)benzamido)pent-4-en-oic
acid
(8b): Same procedure as for 8a. An orange oil is obtained starting from
7b (1.44 g, 4.23 mmol), no purification was required (1.19 g, 79% yield
over the
2 steps). N-(4-Formylhepta-1,6-dien-4-yl)-4-((trimethylsilyl)-
ethynyl) benzamide: 1H NMR (CDCl3, 400 MHz): δ (ppm) 9.43 (s, 1H,
CHO), 7.71-7.67 (m, 2H, HAr), 7.52-7.48 (m, 2H, HAr), 6.81 (s, 1H, NH),
5.62 (ddt, J = 17.1, 10.0, 7.3 Hz, 2H, CH=CH2), 5.17-5.07 (m, 4H,
CH=CH2), 3.07 (dd, J = 14.4, 7.4 Hz, 2H, CH2), 2.64 (dd, J = 14.4, 7.4 Hz,
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10.1002/ejoc.201901350
European Journal of Organic Chemistry
FULL PAPER
oils (minor diastereoisomer 9a: 8 mg, 7% yield; major diastereoisomer
9b: 79 mg, 66% yield). 9a: 1H NMR (CDCl3, 400 MHz): δ (ppm) 8.00-7.93
(m, 2H, HAr), 7.55 (m, 1H, HAr), 7.50-7.43 (m, 2H, HAr), 7.37-7.22 (m, 5H,
HAr), 3.74 (s, 2H, CH2), 2.62-2.43 (m, 4H, CH2, 2 CH), 2.32 (dd, 1H,
J = 13.6, 7.1 Hz, 1H, CH2), 2.25 (dd, 1H, J = 13.9, 6.2 Hz, 1H, CH2), 2.04
(dd, 1H, J = 13.7, 7.1 Hz, 1H, CH2), 1.81 (dd, 1H, J = 13.6, 4.8 Hz, 1H,
CH2), 1.04 (d, J = 6.7 Hz, 3H, CH3). 13C NMR (CDCl3, 100 MHz): δ (ppm)
182.9 (C=O), 159.7 (C=N), 138.6 (CAr), 132.6 (CAr), 129.0 (2 CAr), 128.9
(2 CAr), 128.7 (2 CAr), 128.0 (2 CAr), 127.1 (CAr), 126.2 (CAr), 75.5 (C),
45.3 (CH2), 43.1 (CH), 42.1 (CH2), 37.1 (CH), 36.7 (CH2), 31.9 (CH2),
14.8 (CH3). 9b: 1H NMR (CDCl3, 400 MHz): δ (ppm) 8.01-7.94 (m, 2H,
HAr), 7.62-7.53 (m, 1H, HAr), 7.50-7.43 (m, 2H, HAr), 7.37-7.21 (m, 5H,
HAr), 3.74 (d, J = 0.9 Hz, 2H, CH2), 2.69-2.54 (m, 3H, CH2, 2 CH), 2.50-
2.42 (m, 1H, CH2), 2.19 (dd, 1H, J = 13.7, 6.9 Hz, 1H, CH2), 2.14-2.09 (m,
2H, CH2), 1.91 (dd, 1H, J = 13.7, 5.8 Hz, 1H, CH2), 1.00 (d, J = 6.8 Hz,
3H, CH3). 13C NMR (CDCl3, 100 MHz): δ (ppm) 182.0 (C=O), 159.8
(C=N), 138.5 (CAr), 132.7 (CAr), 129.0 (2 CAr2), 128.9 (2 CAr), 128.6 (2
CAr), 128.0 (2 CAr), 127.1 (CAr), 126.2 (CAr), 74.0 (C), 45.7 (CH2), 43.0
(CH2), 42.5 (CH), 37.8 (CH2), 36.5 (CH), 32.1 (CH2), 15.0 (CH3). IR
(neat): ν = 2924, 1812, 1650, 1452, 1324, 1290 cm-1. HRMS (ESI+): m/z
(M+Na+) calcd for C22H23NNaO2S: 388.1342, found: 388.1343.
added to
a
solution of
9
(90 mg, 0.25 mmol, 30:70 mixture of
diastereoisomers) in DMSO (2 mL) at rt. The reaction mixture was stirred
at 40 °C for 16 h then diluted with EtOAc and brine. The phases were
separated and the aqueous fraction was extracted with EtOAc (2 x 5 mL).
The combined organic layers were dried over anhydrous Na2SO4, filtered
and concentrated in vacuo. Purification by flash chromatography
(Cyclohexane/Et2O 6:4, then 5:5) afforded compound 12 as a 30:70
mixture of two inseparable diastereoisomers (110 mg, 95%, white solid);
mp
= 154-156 °C. From 11: DMPA (2.9 mg, 12 µmol) and
benzylmercaptan (13.5 µL, 115 µmol) were added to a solution of 11 (40
mg, 115 µmol) in degassed DMF (6 mL) at rt. The reaction mixture was
stirred at rt under UV irradiation (365 nm) for 1 h then diluted with EtOAc
and brine. The phases were separated and the aqueous fraction was
extracted with EtOAc (2 x 5 mL). The combined organic layers were dried
over anhydrous Na2SO4, filtered and concentrated in vacuo. Purification
by flash chromatography (Cyclohexane/Et2O 6:4, then 5:5) provided the
spiro compound 12 as a 70:30 mixture of diastereoisomers (50 mg, 92%
yield, white solid). 1H NMR (CDCl3, 400 MHz): δ (ppm) 7.72-7.70 (m, 2H,
HAr), 7.50-7.40 (m, 2H, HAr), 7.39-7.33 (m, 2H, HAr), 7.30-7.15 (m, 11H,
HAr, NH), 7.05 (s, 0.3H, NH), 6.37 (s, 0.7H, NH), 4.36-4.30 (m, 2H, NCH2),
3.68 (d, J = 12.0 Hz, 1H, SCH2), 3.63 (d, J = 12.0 Hz, 1H, SCH2), 2.81
(dd, J = 14.0, 7.1 Hz, 0.3H, CH2), 2.74 (dd, J = 13.7, 6.3 Hz, 0.3H, CH2),
2.50-2.42 (m, 0.7H, CH2), 2.37-2.17 (m, 5.4H, CH2, CH), 2.12-2.06 (m,
0.7H, CH2), 1.86 (dd, J = 13.7, 6.6 Hz, 0.3H, CH2), 1.69 (dd, J = 14.0, 6.1
Hz, 0.3H, CH2), 0.88 (d, J = 6.5 Hz, 0.9H, CH), 0.84 (d, J = 6.0 Hz, 2.1H,
CH3). 13C NMR (CDCl3, 100 MHz): δ (ppm) 174.3 (0.3 C=O), 173.6 (0.7
C=O), 168.1 (0.7 C=O), 167.6 (0.3 C=O), 138.7 (0.3 CAr), 138.7 (0.7 CAr),
138.6 (0.7 CAr), 138.3 (0.3 CAr), 134.2 (0.7 CAr), 133.9 (0.3 CAr), 132.0
(0.3 CAr), 132.0 (0.7 CAr), 128.9 (0.3 CAr), 128.8 (0.7 CAr), 128.7 (0.3 CAr),
128.7 (0.7 CAr), 128.6 (0.3 CAr), 128.6 (0.3 CAr), 128.6 (0.7 CAr), 128.5
(0.7 CAr), 127.4 (0.7 CAr), 127.3 (0.3 CAr), 127.2 (0.7 CAr), 127.2 (0.3 CAr),
127.2 (0.3 CAr), 127.2 (0.7 CAr), 127.1 (0.3 CAr), 127.0 (0.7 CAr), 67.0 (0.7
C), 66.3 (0.3 C), 45.0 (0.3 CH2), 44.5 (0.7 CH2), 43.7 (NCH2), 42.6 (0.3
CH2), 41.3 (0.7 CH2), 41.2 (0.3 CH), 40.6 (0.7 CH), 37.1 (0.7 SCH2), 36.5
(0.3 SCH2), 35.9 (0.3 CH), 34.3 (0.7 CH), 32.7 (0.7 CH2), 32.2 (0.3 CH2),
15.2 (0.7 CH3), 15.1 (0.3 CH3). IR (neat): ν = 3289, 2916, 1654, 1525,
1492, 1313, 1074, 1030 cm-1. HRMS (ESI+): m/z (M+Na+) calcd for
C29H32N2NaO2Si: 495.2077, found: 495.2072.
4,4-Bis(3-(benzylthio)propyl)-2-phenyloxazol-5(4H)-one (10): DMPA
(26 mg, 0.10 mmol) was added to a solution of 5a (241 mg, 1.0 mmol) in
benzylmercaptan (1.2 mL, 10.0 mmol). The reaction mixture was stirred
at rt under UV irradiation (365 nm) for 1 h then diluted with EtOAc and
brine. The phases were separated and the aqueous fraction was
extracted with EtOAc (2 x 5 mL). The combined organic layers were dried
over anhydrous Na2SO4, filtered and concentrated in vacuo. Purification
by flash chromatography (Cyclohexane/Et2O 98:2, then 95:5) afforded
compound 10 (465 mg, 95% yield) as a colorless oil. 1H NMR (CDCl3,
400 MHz): δ (ppm) 8.06-8.00 (m, 2H, HAr), 7.66-7.59 (m, 1H, HAr),
7.58-7.50 (m, 2H, HAr), 7.34-7.26 (m, 8H, HAr), 7.26-7.20 (m, 2H, HAr),
3.68 (s, 4H, SCH2), 2.41 (t, J = 7.1 Hz, 4H, CH2), 2.03-1.89 (m, 4H, CH2),
1.61-1.39 (m, 4H, CH2). 13C NMR (CDCl3, 100 MHz): δ (ppm) 180.1
(C=O), 160.2 (C=N), 138.3 (2 CAr), 132.9 (CAr), 128.9 (2 CAr), 128.8 (4
CAr), 128.5 (4 CAr), 128.0 (2 CAr), 127.0 (2 CAr), 125.7 (CAr), 73.0 (C), 36.3
(2 CH2), 36.1 (2 CH2), 30.9 (2 CH2), 23.5 (2 CH2). IR (neat): ν = 3289,
2916, 1816, 1652, 1495, 1452, 1290, 1073, 1004 cm-1. HRMS (ESI+):
m/z (M+Na+) calcd for C29H31NNaO2S2: 512.1688, found: 512.1687.
N-(4-(Benzylcarbamoyl)-1,7-bis(benzylthio)heptan-4-yl)benzamide
(13): From 10: Benzylamine (9 µL, 82 µmol) was added to a solution of
10 (40 mg, 82 µmol) in DMSO (1 mL) at rt. The reaction mixture was
stirred at 40 °C for 16 h then diluted with EtOAc and brine. The phases
were separated and the aqueous fraction was extracted with EtOAc (2 x
2 mL). The combined organic layers were dried over anhydrous Na2SO4,
filtered and concentrated in vacuo. Purification by flash chromatography
(Cyclohexane/EtOAc 7:3) afforded compound 13 (45 mg, 95% yield) as a
colorless oil. From 11: DMPA (13 mg, 0.10 mmol) was added to a
solution of 11 (174 mg, 0.51 mmol) in benzylmercaptan (0.6 mL,
5.10 mmol). The reaction mixture was stirred at rt under UV irradiation
(365 nm) for 1 h then diluted with EtOAc and brine. The phases were
separated and the aqueous fraction was extracted with EtOAc (2 x 5 mL).
The combined organic layers were dried over anhydrous Na2SO4, filtered
and concentrated in vacuo. Purification by flash chromatography
(Cyclohexane/Et2O 8:2) afforded compound 13 (271 mg, 90% yield) as a
colorless oil. 1H NMR (CDCl3, 400 MHz): δ (ppm) 7.86-7.81 (m, 2H, HAr),
7.78 (s, 1H, NH), 7.55-7.48 (m, 1H, HAr), 7.45-7.41 (m, 2H, HAr), 7.38-
7.16 (m, 15H, HAr), 6.21 (t, J = 5.6 Hz, 1H, NHCH2), 4.49 (d, J = 5.6 Hz,
2H, NHCH2), 3.58 (d, J = 12.0 Hz, 2H, SCH2), 3.54 (d, J = 12.0 Hz, 2H,
SCH2), 2.84-2.71 (m, 2H, CH2), 2.40 (ddd, J = 13.0, 7.1, 5.5 Hz, 2H,
CH2), 2.26 (ddd, J = 13.0, 6.6, 5.4 Hz, 2H, CH2), 1.71-1.54 (m, 4H, CH2),
1.35-1.22 (m, 2H, CH2). 13C NMR (CDCl3, 100 MHz): δ (ppm) 173.1
(C=O), 166.0 (C=O), 138.4 (2 CAr), 137.7 (CAr), 134.9 (CAr), 131.7 (CAr),
129.1 (2 CAr), 128.9 (4 CAr), 128.8 (2 CAr), 128.6 (4 CAr), 128.1 (2 CAr),
N-(4-(Benzylcarbamoyl)hepta-1,6-dien-4-yl)benzamide
(11):
Benzylamine (0.14 mL, 1.24 mmol) was added to a solution of oxazolone
5a (300 mg, 1.24 mmol) in DMSO (6 mL) at rt. The reaction mixture was
stirred at 40 °C for 16 h then diluted with EtOAc and brine. The phases
were separated and the aqueous fraction was extracted with EtOAc (2 x
15 mL). The combined organic layers were dried over anhydrous Na2SO4,
filtered and concentrated in vacuo. Purification by flash chromatography
(Cyclohexane/Et2O 6:4) afforded compound 11 (431 mg, quantitative
yield) as a white solid; mp = 154-156 °C. 1H NMR (CDCl3, 400 MHz): δ
(ppm) 7.75-7.70 (m, 2H, HAr), 7.50-7.45 (m, 1H, HAr), 7.42-7.36 (m, 2H,
HAr), 7.32-7.22 (m, 6H, HAr, NH), 6.92 (t, J = 5.8 Hz, 1H, NH), 5.69 (dddd,
J = 16.1, 11.0, 7.9, 6.7 Hz, 2H, CH=CH2), 5.14-5.04 (m, 4H, CH=CH2),
4.46 (d, J = 5.8 Hz, 2H, CH2N), 3.14 (ddt, J = 14.2, 7.9, 1.1 Hz, 2H, CH2),
2.70 (ddt, J = 14.2, 6.7, 1.3 Hz, 2H, CH2). 13C NMR (CDCl3, 100 MHz): δ
(ppm) 172.5 (C=O), 167.1 (C=O), 138.0 (CAr), 135.0 (CAr), 132.4 (2
CH=CH2), 131.8 (CAr), 128.8 (2 CAr), 128.8 2 (CAr), 127.9 (2 CAr), 127.7
(CAr), 127.0 (2 CAr), 119.9 (2 CH=CH2), 63.4 (C), 44.2 (CH2), 39.9 (CH2).
IR (neat): ν = 3245, 2925, 1745, 1666, 1640, 1599, 1525, 1495, 1313,
1249, 1127 cm-1. HRMS (ESI+): m/z (M+H+) calcd for C22H25N2O2:
349.1911, found: 349.1903.
N-(1-(Benzylcarbamoyl)-3-((benzylthio)methyl)-4-methylcyclo-
pentyl)-benzamide (12): From 9: Benzylamine (27 µL, 0.25 mmol) was
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10.1002/ejoc.201901350
European Journal of Organic Chemistry
FULL PAPER
128.1 (CAr), 127.1 (CAr), 127.06 (2 CAr), 64.0 (C), 44.5 (CH2), 36.2 (2
SCH2), 35.4 (2 CH2), 31.0 (2 CH2), 23.6 (2 CH2). IR (neat): ν = 3341,
2918, 1639, 1510, 1480, 1266 cm-1. HRMS (ESI+): m/z (M+Na+) calcd for
C36H40N2NaO2S2: 619.2423, found: 619.2439.
4-(1-Benzyl-1H-1,2,3-triazol-4-yl)-N-(4-(benzyl-carbamoyl)hepta-1,6-
dien-4-yl)benzamide (16): CuBr (8.2 mg, 57 µmol), benzyl azide (24 µL,
188 µmol) and PMDETA (47 µL, 226 µmol) were successively added to a
solution of 5b (50 mg, 188 µmol) in degassed DMF (1 mL). After stirring
at rt for 16 h, the reaction mixture was diluted with EtOAc and brine. The
aqueous phase was extracted with EtOAc (2 x 2 mL) and the combined
organic layers were washed with brine (3 x 3 mL), dried over anhydrous
MgSO4, filtered and concentrated in vacuo. Purification by flash
chromatography (Cyclohexane/EtOAc 4:1) afforded triazole 16 (45 mg,
59% yield) as a colorless oil. 1H NMR (CDCl3, 400 MHz): δ (ppm) 8.03-
7.98 (m, 2H, HAr), 7.94-7.89 (m, 2H, HAr), 7.78 (s, 1H, C=CH), 7.42-7.30
(m, 5H, HAr), 5.65 (dddd, J = 17.1, 10.1, 7.8, 6.8 Hz, 2H, CH=CH2), 5.58
(s, 2H, NCH2), 5.17 (m, 2H, CH=CH2), 5.10 (m, 2H, CH=CH2), 2.67 (ddt,
J = 13.7, 6.8, 1.2 Hz, 2H, CH2), 2.58 (ddt, J = 13.7, 7.8, 1.0 Hz, 2H, CH2).
13C NMR (CDCl3, 100 MHz): δ (ppm) 179.2 (C=O), 159.8 (C=N), 147.1
(C=CH), 134.8 (CAr), 134.5 (CAr), 130.7 (2 CH=CH2), 129.3 (2 CAr), 129.0
(CAr), 128.6 (2 CAr), 128.2 (2 CAr), 125.9 (2 CAr), 125.2 (CAr), 120.6 (2
CH=CH2), 120.5 (C=CH), 73.8 (C), 54.5 (NCH2), 41.1 (2 CH2). IR (neat):
ν = 3100, 2900, 1815, 1652, 1294, 1048 cm-1. HRMS (ESI+): m/z
(M+Na+) calcd for C24H22N4NaO2: 421.1635, found: 421.1620.
N-(4-(Benzylcarbamoyl)hepta-1,6-dien-4-yl)-4-ethynyl-benzamide
(14): Benzylamine (21 µL, 0.19 mmol) was added to a solution of
oxazolone 5b (50 mg, 0.19 mmol) in DMSO (1 mL) at rt. The reaction
mixture was stirred at 40 °C for 16 h then diluted with EtOAc and brine.
The phases were separated and the aqueous fraction was extracted with
EtOAc (2 x 1 mL). The organic layer was dried over MgSO4, filtered and
concentrated in vacuo. Purification by flash chromatography
(Cyclohexane/EtOAc 85:15) afforded compound 14 (69 mg, 97% yield)
as a white solid; mp = 107-109°C. 1H NMR (CDCl3, 400 MHz): δ (ppm)
7.71-7.67 (m, 2H, HAr), 7.54-7.49 (m, 2H, HAr), 7.40 (bs, 1H, NH), 7.35-
7.24 (m, 5H, HAr), 6.95 (t, J = 5.7 Hz, 1H, NHCH2), 5.68 (m, 2H, CH=CH2),
5.13-5.06 (m, 4H, CH=CH2), 4.47 (d, J = 5.7 Hz, 2H, NHCH2), 3.23 (ddt,
J = 14.2, 7.9, 1.2 Hz, 2H, CH2), 3.20 (s, 1H, C≡CH), 2.67 (ddt, J = 14.2,
6.7, 1.2 Hz, 2H, CH2). 13C NMR (CDCl3, 100 MHz): δ (ppm) 172.3 (C=O),
166.1 (C=O), 137.9 (CAr), 135.0 (CAr), 132.4 (2 CAr), 132.2 (2 CH=CH2),
128.8 (CAr), 127.9 (CAr), 127.7 (CAr), 126.9 (CAr), 125.6 (CAr), 119.9 (2
CH=CH2), 82.8 (C≡CH), 79.7 (C≡CH), 63.5 (C), 44.2 (NCH2), 39.8 (2
CH2). IR (neat): ν = 3279, 3086, 2952, 1644, 1629, 1540, 1499, 1313,
1279, 1238 cm-1. HRMS (ESI+): m/z (M+Na+) calcd for C24H24N2NaO2:
395.1730, found: 395.1720.
2-(4-(1-Benzyl-1H-1,2,3-triazol-4-yl)phenyl)-4,4-bis(3-(benzylthio)-
propyl)oxazol-5(4H)-one (17): DMPA (4.6 mg, 18 µmol) was added to a
solution of 16 (70 mg, 176 µmol) in benzylmercaptan (0.21 mL,
1.76 mmol). The reaction mixture was stirred at rt under UV irradiation
(365 nm) for 1 h then diluted with EtOAc and brine. The phases were
separated and the aqueous fraction was extracted with EtOAc (2 x 2 mL).
The combined organic layers were dried over anhydrous Na2SO4, filtered
and concentrated in vacuo. Purification by flash chromatography (neat
CH2Cl2) afforded compound 17 (104 mg, 91% yield) as a colorless oil. 1H
NMR (CDCl3, 400 MHz): δ (ppm) 8.03-7.98 (m, 2H, HAr), 7.96-7.92 (m,
2H, HAr), 7.76 (s, 1H, C=CH), 7.45-7.32 (m, 5H, HAr), 7.30-7.15 (m, 10H,
HAr), 5.61 (s, 2H, NCH2), 3.66 (d, J = 12.0 Hz, 2H, SCH2), 3.62 (d, J =
12.0 Hz, 2H, SCH2), 2.37 (t, J = 7.2 Hz, 4H, CH2), 1.98-1.84 (m, 4H, CH2),
1.55-1.35 (m, 4H, CH2). 13C NMR (CDCl3, 100 MHz): δ (ppm) 180.1
(C=O), 160.1 (C=N), 147.2 (C=CH), 138.4 (2 CAr), 135.0 (CAr), 134.5
(CAr), 129.4 (2 CAr), 129.1 (CAr), 128.9 (4 CAr), 128.7 (2 CAr), 128.6 (4 CAr),
128.4 (2 CAr), 127.1 (2 CAr), 126.0 (2 CAr), 125.1 (CAr), 120.5 (C=CH),
73.1 (C), 54.6 (NCH2), 36.5 (2 CH2), 36.2 (2 SCH2), 31.0 (2 SCH2), 23.6
(2 CH2). IR (neat): ν = 2925, 1722, 1659, 1495, 1458, 1238 cm-1.
4-(1-Benzyl-1H-1,2,3-triazol-4-yl)-N-(4-(benzyl-carbamoyl)hepta-1,6-
dien-4-yl)benzamide (15): From 14: CuBr (4.6 mg, 32 µmol), benzyl
azide (13 µL, 0.107 mmol) and PMDETA (27 µL, 0.129 mmol) were
successively added to a solution of 14 (40 mg, 0.107 mmol) in degassed
DMF (0.6 mL). After stirring at rt for 16 h, the reaction mixture was diluted
with EtOAc and brine. The aqueous phase was extracted with EtOAc (2 x
2 mL) and the combined organic layers were washed with brine (3 x 3
mL), dried over anhydrous MgSO4, filtered and concentrated in vacuo.
Filtration through a pad of silicagel afforded triazole 15 (54 mg,
quantitative yield) as a white solid. From 5b: CuBr (8.2 mg, 57 µmol),
benzyl azide (24 µL, 0.188 mmol), PMDETA (47 µL, 0.226 mmol) and
benzylamine (21 µL, 0.188 mmol) were successively added to a solution
of 5b (50 mg, 0.188 mmol) in degassed DMF (1 mL). After stirring at
40 °C for 16 h, the reaction mixture was diluted with EtOAc and brine.
The aqueous phase was extracted with EtOAc (2 x 2 mL) and the
combined organic layers were washed with brine (3 x 3 mL), dried over
anhydrous MgSO4, filtered and concentrated in vacuo. Purification by
flash chromatography (Cyclohexane/EtOAc 7:3) afforded compound 15
(90 mg, 95% yield) as a white solid. From 16: Benzylamine (7 µL, 68
µmol) was added to a solution of oxazolone 16 (27 mg, 68 µmol) in
DMSO (0.5 mL) at rt. The reaction mixture was stirred at 40 °C for 16 h
then diluted with EtOAc and brine. The phases were separated and the
aqueous fraction was extracted with EtOAc (2 x 2 mL). The organic layer
was dried over MgSO4, filtered and concentrated in vacuo. Purification by
flash chromatography (Cyclohexane/EtOAc 7:3) afforded compound 15
(33 mg, 96% yield) as a white solid. 1H NMR (CDCl3, 400 MHz): δ (ppm)
7.87-7.81 (m, 2H, HAr), 7.80-7.76 (m, 2H, HAr), 7.73 (s, 1H, C=CH), 7.43-
7.36 (m, 3H, HAr, NH), 7.42-7.24 (m, 10H, HAr), 6.99 (t, J = 5.7 Hz, 1H,
NHCH2), 5.72 (dddd, J = 16.3, 10.8, 7.8, 6.8 Hz, 2H, CH=CH2), 5.57 (s,
2H, NCH2), 5.16-5.05 (m, 4H, CH=CH2), 4.49 (d, J = 5.7 Hz, 2H, NHCH2),
3.20 (ddt, J = 14.3, 7.8, 1.1 Hz, 2H, CH2), 2.72 (ddt, J = 14.3, 6.8, 1.3 Hz,
2H, CH2). 13C NMR (CDCl3, 100 MHz): δ (ppm) 172.4 (C=O), 166.5
(C=O), 147.3 (C=CH), 138.0 (CAr), 134.5 (CAr), 134.3 (CAr), 133.8 (CAr),
132.4 (2 CH=CH2), 129.3 (2 CAr), 129.0 (CAr), 128.8 (2 CAr), 128.2 (2 CAr),
127.9 (2 CAr), 127.7 (CAr), 127.6 (2 CAr), 125.8 (2 CAr), 120.3 (C=CH),
119.8 (2 CH=CH2), 63.5 (C), 54.5 (NCH2), 44.1 (NHCH2), 39.9 (2 CH2).
IR (neat): ν = 3346, 3070, 1644, 1514, 1488, 1458, 1235 cm-1. HRMS
(ESI+): m/z (M+Na+) calcd for C31H31N5NaO2: 528.2370, found: 528.2373.
4-(1-Benzyl-1H-1,2,3-triazol-4-yl)-N-(4-(benzyl-carbamoyl)-1,7-bis-
(benzylthio)heptan-4-yl)benzamide (18): From 15: DMPA (2.0 mg, 12
µmol) was added to
a solution of 15 (60 mg, 0.12 mmol) in
benzylmercaptan (0.14 mL, 1.20 mmol). The reaction mixture was stirred
at rt under UV irradiation (365 nm) for 1 h then diluted with EtOAc and
brine. The phases were separated and the aqueous fraction was
extracted with EtOAc (2 x 2 mL). The combined organic layers were dried
over anhydrous Na2SO4, filtered and concentrated in vacuo. Purification
by flash chromatography (Cyclohexane/EtOAc 95:5 to 1:1) afforded
compound 18 (86 mg, 96% yield) as
a colorless oil. From 17:
Benzylamine (10 µL, 93 µmol) was added to a solution of oxazolone 17
(60 mg, 93 µmol) in DMSO (2 mL) at rt. The reaction mixture was stirred
at 40 °C for 16 h then diluted with EtOAc and brine. The phases were
separated and the aqueous fraction was extracted with EtOAc (2 x 5
mL).The organic layer was dried over MgSO4, filtered and concentrated
in vacuo. Filtration on a pad of silicagel (Cyclohexane/EtOAc 7:3)
afforded compound 18 (67 mg, 96% yield) as a colorless oil. Sequential
“one pot” from 5b: CuBr (8.2 mg, 57 µmol), benzyl azide (24 µL, 188
µmol), PMDETA (47 µL, 226 µmol) and benzylamine (21 µL, 188 µmol)
were successively added to a solution of 5b (50 mg, 188 µmol) in
degassed DMF (1 mL). After stirring at 40 °C for 16 h, the reaction
mixture was diluted with EtOAc and brine. The organic layer was dried
over anhydrous MgSO4, filtered and concentrated in vacuo.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901350
European Journal of Organic Chemistry
FULL PAPER
Benzylmercaptan (0.22 mL, 1.90 mmol) and DMPA (3.0 mg, 19 µmol)
were added and the reaction mixture was stirred at rt under UV
irradiation (365 nm) for 1 h. EtOAc and brine were added. The phases
were separated and the aqueous fraction was extracted with EtOAc (2 x
5 mL). The combined organic layers were dried over anhydrous MgSO4,
filtered and concentrated in vacuo. Purification by flash chromatography
(Cyclohexane/EtOAc 95:5 to 1:1) afforded compound 18 (120 mg, 85%
yield) as a colorless oil. 1H NMR (CDCl3, 400 MHz): δ (ppm) 7.88-7.82 (m,
4H, HAr), 7.80 (bs, 1H, NH), 7.72 (s, 1H, C=CH), 7.43-7.14 (m, 20H, HAr),
6.39 (t, J = 5.7 Hz, 1H, NHCH2), 5.57 (s, 2H, NCH2), 4.49 (d, J = 5.7 Hz,
1H, NHCH2), 3.57 (d, J = 12.0 Hz, 2H, SCH2), 3.53 (d, J = 12.0 Hz, 2H,
SCH2), 2.76 (m, 2H, CH2), 2.39 (ddd, J = 12.6, 6.5, 5.7 Hz, 2H, CH2),
2.26 (dt, J = 12.7, 7.2 Hz, 2H, CH2), 1.72-1.52 (m, 4H, CH2), 1.35-1.25
(m, 2H, CH2). 13C NMR (CDCl3, 100 MHz): δ (ppm) 173.1 (C=O), 165.4
(C=O), 147.3 (C=CH), 138.4 (CAr), 137.7 (CAr), 134.5 (2 CAr), 134.3 (2
CAr), 133.7 (CAr), 129.3 (2 CAr), 129.0 (2 CAr), 128.9 (4 CAr), 128.6 (4 CAr),
128.2 (2 CAr), 128.0 (2 CAr), 128.0 (2 CAr), 127.6 (2 CAr), 127.0 (2 CAr),
125.8 (2 CAr), 120.3 (C=CH), 64.1 (C), 54.4 (NCH2), 44.4 (NHCH2), 36.1
(2 SCH2), 35.3 (2 CH2), 31.0 (2 CH2), 23.6 (2 CH2). IR (neat): ν = 3353,
2921, 1644, 1484, 1458, 1231 cm-1. HRMS (ESI+): m/z (M+H+) calcd for
C45H48N5O2S2: 754.3244, found: 754.3253.
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Acknowledgments
The authors thank S. Bricaud, P. Gangnery, F. Legros, C.
Jacquemmoz and E. Mebold for technical assistance and
analyses. J. Caillé gratefully thanks the “Ministère de
l’enseignement supérieur et de la recherche” for PhD fellowship.
M. Pantin thanks the “Université Bretagne Loire” for postdoctoral
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This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901350
European Journal of Organic Chemistry
FULL PAPER
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901350
European Journal of Organic Chemistry
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FULL PAPER
Linkers, click chemistry
Mathilde Pantin, Julien Caillé, Fabien
Boeda, Laurent Fontaine, Morwenna S.
M. Pearson-Long,* Philippe Bertus*
Page No. – Page No.
New oxazolone-based heteromultifunctional linkers were synthesized using a zinc-
mediated double functionalization of nitriles as the key step. The orthogonality of
the functional groups was demonstrated by conducting sequential or simultaneous
multi-component reactions with amines, thiols and azides, in respect to the concept
of click chemistry.
Heteromultifunctional oxazolones as
versatile linkers for click chemistry
reactions
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