Convenient and efficient synthesis of functionalized unsymmetrical alkynyl sulfides

Article abstract of DOI:10.1039/c6ra19440k

We developed a simple and efficient method for the synthesis of functionalized unsymmetrical alkynyl sulfides under mild conditions in good yields. The designed method is based on the reaction of 5,5-dimethyl-2-thioxo-1,3,2-dioxaphosphorinan-2-disulfanyl derivatives with lithium acetylides. The developed method allows the preparation of unsymmetrical alkynyl sulfides bearing additional hydroxyl, carboxyl, or amino functionalities.

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Convenient and efficient synthesis of functionalized
unsymmetrical alkynyl sulfides
J. Doroszuk,a M. Musiejuk,a S. Demkowicz,a J. Rachon,a and D. Witt a*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
We developed a simple and efficient method for the synthesis of biomolecules and polymers.6 In this context, the development
functionalized unsymmetrical alkynyl sulfides under mild of new synthetic methods to access alkynes and their
conditions in good yields. The designed method is based on the derivatives efficiently under user-friendly conditions is highly
reaction of 5,5-dimethyl-2-thioxo-1,3,2-dioxaphosphorinan-2- desirable.
disulfanyl derivatives with lithium acetylides. The developed Driven by the exceptional reactivity of sulfur and its
method allows the preparation of unsymmetrical alkynyl sulfides importance in biology, medicine, and materials science,7
bearing additional hydroxyl, carboxyl, or amino functionalities.
recent research efforts targeted a series of thiol-based
transformations including thiol alkylations and the thiol
addition to alkenes and alkynes respectively.8 Unlike the well-
established S-Csp3 bond forming reactions, existing methods to
construct S-Csp bonds are rare in number and often lack
generality or require harsh conditions.
Introduction
The development of practical and versatile methods for
introduction of functional groups into molecules to modify
their properties is one of the most important task of organic
chemistry. The easy to perform reactions that do not require
highly specialized synthetic skills have a particularly broad
impact to other fields such as medicine, biology, or materials
science. From this point of view, among all functional groups in
organic chemistry, alkynes occupy a privileged position.1
Although alkynes contain one of the simplest functional group,
two carbon atoms connected with triple bond, the reactivity of
that bond makes alkynes exceptionally useful in organic
synthesis. They were applied in the stereoselective
construction of the carbon backbone of complex natural
products,2 bulk chemical synthesis based on acetylene gas3
and in the variety of complexity-enhancing metal-catalyzed
cyclization reactions to provide carbo- and heterocycles.4 The
electronic properties of alkynes have found also wide
applications in preparation of organic materials and dyes.5
Moreover, their [3+2] cycloaddition with azides is recognized
as one of the best biorthogonal conjugation method to modify
Alkynyl sulfides can be obtained by methods utilize transition-
metal catalysts, such as the copper-catalyzed carbon sulfur
coupling between terminal alkynes and disulfides,9 or as in the
elegant study by Yamaguchi, the use of catalytic rhodium to
achieve C-S bond formation by C-H and S-S bond metathesis
(Scheme 1, A).10 Alternatively, a range of processes utilize
alkenyl11 or alkynyl12 halides bearing leaving groups that
undergo elimination under strongly basic conditions to furnish
the desired alkynyl sulfides (Scheme 1, B). Consequently, the
limited functional group tolerance exhibited by these methods
is not surprising as they require harsh conditions, proceed via
highly reactive intermediates, or involve the use of sensitive
catalytic systems. Recently, Waser has developed a thiol-
alkynylation procedure utilizing the hypervalent iodine alkyne
transfer reagent TIPS-ethynylbenziodoxolone (Scheme 1, C).13
Although the method is highly chemoselective as a vast array
of functional groups are tolerated, the problems associated
with preparation and stability hypervalent iodine alkyne
transfer reagent are the major disadvantages of that
transformation. Currently, the most common methods to form
alkynyl sulfides require a prefunctionalization of the thiol
(Scheme 1, D). These methods are generally based on
nucleophilic substitutions between highly reactive lithium
acetylide intermediates with pre-activated thiols or disulfide
species.14 The major drawback of that approached emerges
from availability and long term stability of pre-activated thiols.
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material and polymer science as an alternative tool to the
current array of thiol-functionalization reactions. In this
context, we set out to investigate the feasibility of more
convenient and experimentally practical method to gain access
to alkynyl sulfides.
Results and discussion
The terminal alkynes can be easily converted into the 1-Cu(I)
acetylides.27 The presence of additional groups (as carbonyl,
carboxyl or hydroxyl) did not disturb the formation of
corresponding salts. Moreover, these compounds were stored
in a bottle and no notable decomposition was observed within
one year. We began our study with copper (I) phenylacetylide
1a as starting substrate while screening different disulfanyl
derivatives reagents capable to produce corresponding
phenylethynyl sulfides
3
(Scheme 2).
R
CHCl3
R
Y
Ph
Y
Ph
Cu
+
R
Y
N2, reflux
15 min.
3
1a
2
R
Y
R
Y
O
O
O
S
S
S
S
O
O
O
S
S
Ph
C12H25
Ph
P
P
P
S
S
O
O
S
2a
2c
2b
O
S
S
O
P
S
N
N
S
O
S
S
Ph
S
S
2d
S
O
2f
O
S
S
S
Ph
2e
Ph
Se
Ph
S
Ph
Se
2g
2h
Scheme 2. The reaction of copper (I) phenylacetylide 1a with disulfanyl
derivatives
Scheme 1. Previously reported methods for the synthesis of alkynyl sulfides (A-D)
and our new approach (E)
2.
Unfortunately, in the most cases the reaction did not occur or
provided complex mixture without formation of compound
We have previously demonstrated the preparation of
3.
functionalized
unsymmetrical
molecules,
such
as
dialkyldisulfanes,15 alkyl-aryl disulfanes,16 ‘bioresistant’
disulfanes,17 the unsymmetrical disulfanes of L-cysteine and L-
cystine,18 and diaryldisulfanes,19 based on the readily available
electophilic 5,5-dimethyl-2-thioxo-1,3,2-dioxaphosphorinane-
The only successful transformation was the reaction of copper
(I) phenylacetylide with phosphorodithioic acid disulfane 2a
when the expected product 3a was isolated in 67% yield.
Additionally, we have accomplished the synthesis of 3a by
2-disulfanyl derivatives 2 20
phosphorodithioic acid were also convenient for the
preparation of
-sulfenylated carbonyl compounds,21
functionalized phosphorothioates,22 as well as symmetrical23-24
and unsymmetrical25-26 trisulfanes. All these transformations
are based on the electrophilic properties of disulfanyl
.
These disulfanyl derivatives of
independent
method
based
on
the
phenylethynylphenyliodonium tosylate28 to confirm the
structure of the final product (Scheme 3).
α
derivatives of phosphorodithioic acid 2, so we expected that
also reaction with nucleophilic acetylides should provide
corresponding alkynyl sulfides (Scheme 1, E). Furthermore, the
development of a robust, efficient, and orthogonal alkynyl
sulfides synthesis is particularly attractive to the field of
2 | J. Name., 2012, 00, 1-3
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O
O
S
S
S
S
O
O
The reaction of electrophilic disulfanyl derivatives
lithium acetylides was expected to produce the
corresponding alkynyl sulfides with higher yield due to the
2 and
Ph
Cu
P
P
5
1a
3
2a
limited formation of bis-acetylenes
summarized in Table 2.
4.
The results are
CHCl3
N2, reflux
15 min.
67%
Table 2. Reaction of Lithium Acetylides 5 with disulfanes 2
O
O
S
S
S
O
O
R2
P
P
S
R2
S
Ph
S
R1
Li
R1
2
THF, rt, 30 min.
3a
5
3
Entry R1
R2
Yieldb of 3
(78) 3a
CHCl3 / H2O
TEBA
rt, 30 min.
72%
1
2
3
Ph-5a
2a
2a
2a
PhCH2OCH2-5b
BocNHCH2-5c
(75) 3b
(60) 3c
S
O
OTs
Ph
I
P
S
Na
Ph
O
Scheme 3. The synthesis of 1-[(5,5-dimethyl-2-thioxo-1,3,2-dioxaphosphorinan-
2-yl)sulfanyl]-2-phenylacetylene 3a
4
Ph-5a
CH3(CH2)11-2b
CH3(CH2)11-2b
CH3(CH2)11-2b
HO(CH2)11-2i
(99) 3d
(83) 3e
(57) 3f
(63) 3g
(55) 3h
(50) 3i
5
PhCH2OCH2-5b
BocNHCH2-5c
Ph-5a
6
We examined the reactivity of functionalized copper acetylides
7
1
with disulfane 2a. The results are summarized in the Table 1.
8
PhCH2OCH2-5b
BocNHCH2-5c
Ph-5a
HO(CH2)11-2i
9
THPO(CH2)11-2l
HO2C(CH2)11-2j
HO2C(CH2)11-2j
Table 1. Reaction of 1-Copper (I) acetylides 1 with disulfane 2aa.
10
11
12
13
14
15
16
17
18
19
20
(72) 3j
(73) 3k
(51) 3l
PhCH2OCH2-5b
BocNHCH2-5c
Ph-5a
O
O
S
S
S
S
O
O
MeO2C(CH2)11-2m
4-CH3-C6H4-2k
4-CH3-C6H4-2k
4-CH3-C6H4-2k
CH3(CH2)11-2b
CH3(CH2)11-2b
CH3(CH2)11-2b
2-naphthyl-2n
P
P
R
Cu
+
(98) 3m
(89) 3n
(78) 3o
(91) 3p
(100) 3r
(54) 3s
(86) 3t
(100) 3u
PhCH2OCH2-5b
BocNHCH2-5c
4-MeO-2-MeC6H3-5d
(CH3)2CHCH2CH2-5e
EtO2C-5f
1
CHCl3
N2, reflux
15 min.
2a
(CH3)2CHCH2CH2-5e
(CH3)2CHCH2CH2-5e
S
O
P
+
R
R
R
S
O
2o
21
4-NO2-C6H4-5g
CH3(CH2)11-2b
(0) 3w
3
4
a
Conditions: Lithium acetylide 5 (1.0 mmol), TMEDA (1.0 mmol), disulfane 2 (1.1
Entry
R
Yieldb (%)
mmol), 12 mL of THF, rt 30 min. under N2.b Isolated yields in parenthesis.
3
4
1
2
3
Ph- 1a
67
40
30
30
55
40
The lithium acetylides
5
were generated from the
PhCH2OCH2- 1b
BocNH-CH2- 1c
corresponding terminal alkynes and BuLi in the presence of
N,N,N,’N’-tetramethylethylenediamine (TMEDA) in THF to
avoid the potential aggregation of lithium salts. The lithium
phenylacetylide 5a was obtained at -78 °C, -35 °C and 0°C. The
subsequent reaction with 2a provided product 3a in 76, 81 and
78% yields respectively. We did not observed substantial
influence of temperature on the generation of acetylide 5a
and the yield of final product 3a. That is why, acetylides 5b-g
were generated at 0°C. In the case of disulfanes 2i and 2j with
acidic protons (OH and CO2H respectively, Table 2 entries 7-8
and 10-11) the two fold excess of 5a and 5b was used. It was
also possible to treat 2i and 2j with NaH before addition to
a
Conditions: copper alkyne 1 (1.0 mmol), disulfane 2a (1.0 mmol), 10.0 mL of
chloroform, reflux 15 min. under N2.b Isolated yields.
As the data in Table 1 demonstrate, the yield of product
3 is
moderate (30-67%) and the reaction is hampered by the
formation of dimer (30-55%). Although acetylides are
4
1
stable and readily available their application in the alkynyl
sulfides synthesis, under developed conditions, seems to be
limited by an oxidative coupling that produces bis-acetylenes
4
.
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solution of 5a or 5b in THF. Both methods provided anhydrous THF (10 mL) at 0 °C under N2. After 5 min, a solution
appropriate alkynyl sulfides 3g 3h and 3j 3k with comparable of 1-[(5,5-dimethyl-2-thioxo-1,3,2-dioxaphosphorinan-2-
,
,
yield respectively. However, the generation of 5c from N-Boc yl)disulfanyl]dodecane 2b (0.438 g, 1.1 mmol) in anhydrous
propargylamine required the using of two equivalents of BuLi THF (2 mL) was added. The mixture was stirred at r.t. for 30
(Table 2 entries 3, 6, 9, 12, 15). Moreover, the corresponding min. The reaction was quenched by addition of MeOH (1 mL)
alkynyl sulfides 3i and 3l were obtained when hydroxyl and and evaporated under vacuum. The residue was purified by
carboxyl groups were protected in disulfanes 2l and 2m (THP column chromatography (SiO2, petroleum ether, Rf = 0.6) to
or methyl ester respectively, Table 2 entries 9 and 12). The give 3d as a colorless oil; yield: 0.300 g (99%).
corresponding alkynyl sulfides
3
can be obtained from alkyl, IR (ATR): 2900 (s), 2850 (s) (C-H), 2170 (w) (C≡C), 1600 (w),
produced from 1450 (w), 1370 (w), 750 (m), 700 (m) cm–1
aryl acetylides and disulfanyl derivatives
5
2
alkyl, aryl and heteroarylthiols. When electron-withdrawing 1H NMR (500 MHz, CDCl3): δ = 0.89 (t, J = 7.0 Hz, 3H, CH3),
group was present in the acetylide 5e, the corresponding 1.20-1.40 (m, 16H, CH2), 1.46 (qu, J =7.0 Hz, 2H, CH2), 1.8 (qu, J
product 3s was obtained in moderate yield (Table 2 entry 18). =7.4 Hz, 2H, CH2), 2.81 (t, J =7.3 Hz, 2H, SCH2), 7.26-7.35 (m,
However, reaction of lithium 4-nitrophenylacetylide 5f with 3H, Ar), 7.40-7.45 (m, 2H, Ar).
disulfane 2b did not produce expected product 3w (Table 2 13C NMR (125 MHz, CDCl3): δ= 131.4, 128.2, 127.9, 123.6, 92.8,
entry 21). Both starting materials were consumed and 79.7, 35.8, 31.9, 29.6, 29.6, 29.6, 29.5, 29.3, 29.3, 29.1, 28.2,
formation of complex reaction mixture was observed. The 22.7, 14.1; signals: 19 expected, 18 observed.
same result was obtained when the reaction was performed at HRMS (ESI): m/z [M + H]+calcd for C20H31S: 303.2146; found:
-78 °C. The influence of other electron-withdrawing groups on 303.2152.
the course of the reaction is under investigation. On other
hand, the presence of electron-donating groups on the
Acknowledgments
phenylacetylide 5d did not disturb the formation of alkynyl
sulfide 3p and the product was isolated in 91% yield (Table 2
We gratefully acknowledge the National Science Centre (NCN)
for financial support (grant no. 2015/19/B/ST5/03359)
entry 16). The preparation of alkynyl sulfides
3 from disulfanyl
derivatives 2 and lithium acetylides 5 is very convenient
because both starting materials are stable and readily
available. The transformation tolerates the presence of
additional hydroxyl, carboxyl and amino groups. However, the
presence of acidic protons in the starting materials may
require the using of larger quantity of base to avoid the
protonation of acetylides anions.
Notes and references
1
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Conclusions
In summary, we developed an efficient and convenient
method for the preparation of unsymmetrical alkynyl sulfides
directly from the readily available disulfanyl derivatives of
phosphorodithioic acid and functionalized alkynes in the
3
2
5
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presence of TMEDA and BuLi. A variety of functional groups is
tolerated, including the hydroxyl, carboxyl, and protected
amino, hydroxyl and carboxyl group. Reactions of lithium
acetylides
TMEDA in THF at rt were generally complete within 30 minutes
and gave unsymmetrical alkynyl sulfides exclusively in good
5 with a variety of disulfanes 2 in the presence of
3
or very good yield after isolation. The simplicity and good
yields render this method one of the most attractive
approaches to the preparation of functionalized
unsymmetrical alkynyl sulfides.
Experimental
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A typical procedure for the preparation of alkynyl sulfide 3d and
representative analytical data
BuLi (2.5M, 0.44 mL, 1.1 mmol) was added to a solution of
phenylacetylene (0.11 mL, 1.0 mmol) and N,N,N,’N,’-
tertamethylethylenediamine (TMEDA) (0.15 mL, 1.0 mmol) in
4 | J. Name., 2012, 00, 1-3
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