Synthesis and Photocatalytic Reactivity of Vinylsulfonium Ylides

Article abstract of DOI:10.1021/acs.joc.6b01073

Although sulfur ylides are textbook reagents in organic synthesis, surprisingly little variation of substituents on sulfur is usually observed. In particular, vinylsulfonium ylides have been neglected so far. Herein, we present a study on their synthesis and reactivity, including interesting behavior under photocatalytic conditions.

Full text of DOI:10.1021/acs.joc.6b01073

Article
pubs.acs.org/joc
Synthesis and Photocatalytic Reactivity of Vinylsulfonium Ylides
Immo Klose, Antonio Misale, and Nuno Maulide*
Institute of Organic Chemistry, University of Vienna, Wahringer Strasse 38, 1090 Vienna, Austria
̈
S
* Supporting Information
ABSTRACT: Although sulfur ylides are textbook reagents in
organic synthesis, surprisingly little variation of substituents on
sulfur is usually observed. In particular, vinylsulfonium ylides
have been neglected so far. Herein, we present a study on their
synthesis and reactivity, including interesting behavior under
photocatalytic conditions.
Scheme 1. Comparison of Different Families of Sulfonium
Ylides
INTRODUCTION
■
Sulfur ylides continue to be important synthetic intermediates
since their introduction in organic synthesis more than half a
century ago. They are often the default reagents for the for-
mation of small-sized carbo- or heterocycles,1 most prominently
via the Corey−Chaykovsky−Johnson2 family of reactions. Such
classical processes are based on the carbenoid-type reactivity of
sulfur ylides. Many additional rearrangements3 involving sulfur
ylides have been reported.
Recently, we and others have reported that sulfur ylides are
particularly versatile substrates for noble transition metal catalysis,
particularly gold(I).4,5 Yet, most sulfur ylides employed in those
works possess very little structural diversity regarding the sub-
stituents carried by sulfur itself; in fact, almost invariably, aromatic
(Ph) or simple methyl groups are used. On one hand, this lack of
functionality is related to the number of reactions which ulti-
mately lead to a loss of the sulfide moiety during the reaction,
with any substituents on sulfur thus ending up among the
byproducts. On the other hand, sulfur ylides are generally
prepared through deprotonation of sulfonium salts6 or the
reaction of carbenes7 with sulfides, all methods which might not
lend themselves to dramatic structural variation.
β-ketoester 2 by electrophilic activation (Scheme 2).8,12 Even
though several side reactions could be anticipated,13 the
desired vinylsulfonium ylide 3a was easily obtained when
a
Scheme 2. Preparation of Vinylsulfonium Ylide 3
During our investigation of synthesis and reactivity of different
sulfonium ylides,8 we were interested in cases in which the
substituent on sulfur is unsaturated but not aromatic (Scheme 1).
While vinylsulfonium salts have been exploited as versatile two-
carbon homologating agents,9 vinylsulfonium ylides have been
neglected so far. Herein, we present a study on the synthesis and
reactivity of vinylsulfonium ylides, including interesting behavior
under photocatalytic10 conditions.
a
Yields refer to isolated material. Reactions were conducted on a
5.0 mmol scale, ketoester (1.0 equiv), phenyl vinylsulfoxide (1.0 equiv),
Tf2O (1.1 equiv), DCM (0.1 M), −78 °C to rt, 12 h.
RESULTS AND DISCUSSION
■
In our design, a phenyl substituent was employed to enhance
the stability of the ylide.11 Preparation of the lead compound
3a was envisaged through direct coupling of commercially
available phenyl vinylsulfoxide 1 and the corresponding
Special Issue: Photocatalysis
Received: May 8, 2016
© XXXX American Chemical Society
A
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Tf2O was employed as activating agent, although in a modest
36% yield.
In that reaction, a phenyl group was transferred to oxygen upon
microwave irradiation, in what is an example of the Smiles
rearrangement.15 Following this thermal activation procedure
for 3a, the reaction also took place smoothly; however, under
these conditions, double bond isomerization is observed and
the product was obtained as a mixture of E- and Z-isomers.
For this transformation, mechanisms have to be considered for
both the catalytic and thermal variants.
In the presence of a π-Lewis acid catalyst, activation of the
vinyl group and subsequent 5-exo-trig or 6-endo-trig cyclization
is feasible (Scheme 3, left). In the first case, simple elimination
of the sulfonium moiety in 6 delivers the vinyl ether, whereas in
the latter case, a metal carbene 7 could be formed, which after
formal elimination and protodeauration will afford the same
product. We reasoned that differentiation between these two
pathways might be achieved by a labeling experiment.
With the desired vinylsulfonium ylide in hand, we turned to
the examination of its reactivity. Given our prior experience
with gold catalysis,5a−e we naturally started our investigations in
that direction. Treatment of ylide 3a with 5 mol % of the
Echavarren catalyst14 4 in toluene resulted in clean and full
conversion into a new product. Remarkably, no carbon−carbon
bond was formed, in contrast to what we had previously
observed on substrates carrying distal olefins.5a−c Instead, the
vinyl ether 5a was formed in what appears to be a S- to O-vinyl
migration. The structure was unambiguously assigned as (Z)-5a
by X-ray analysis (Figure 1).
As vinylsulfoxides have been reported to undergo metala-
tion α to sulfur,16 α-deuterated sulfoxide d-1 appeared to be a
readily accessible labeled derivative. Indeed, deprotonation with
LDA and subsequent quenching with deuterium oxide gave the
desired labeled compound d-3a with 90% deuterium incorpo-
ration (Scheme 4). Conversion to the sulfur ylide proceeded as
described previously, setting the stage for the vinyl transfer step.
In the event, catalytic rearrangement of d-3a produced regio-
isomer d-(Z)-5a exclusively, ruling out possible six-membered
cyclic intermediates.
Remarkably, the thermal variant also led to the labeled
regioisomer d-5a, ruling out an otherwise mechanistically ap-
pealing [3,3] sigmatropic rearrangement (Scheme 3, right).
In these cases, a Smiles-like addition−elimination mechanism
seems very unlikely due to the instability of a theoretical
methylide intermediate. Nevertheless, in a concerted process,
this would be akin to a vinylic SN2 reaction.17 Since an SN2
σ mechanism would be prohibited by the impossibility of
forming an all-in-plane transition state within a cyclic structure,
a concerted SN2 π mechanism could be operative. This is
further re-inforced by the fact that “hard” oxygen-based nucleo-
philes have been shown to prefer SN2 π pathways in
calculations.17b A concerted mechanism is also known in
some cases of the related Smiles rearrangement15c and has also
been suggested recently for the sulfur to oxygen migration in
the Julia−Kocienski reaction.18 Furthermore, a concerted
process would also be an example of a [1,4]-sigmatropic
rearrangement19 with an aromatic transition state (Figure 2).20
Inspired by the rise of photocatalysis in recent years, we
investigated how a divinyl ether such as 5a would react under
SET oxidation. Vinyl ether 5a was consequently subjected to
LED irradiation using the standard [Ru(bpy)3]2+ catalyst.
Surprisingly, in the presence of common oxidative or reductive
quenchers, no reaction except isomerization of the double bond
was observed (Table 2). After additional investigation, it was
found that when the solution was not degassed or oxygen was
allowed to enter the reaction, full conversion of the starting
material was observed. The main product under these oxidative
conditions was identified to be α,β-diketoester 8a (Table 2).21
The conversion was not limited to the use of a ruthenium
photocatalyst, as other common catalysts such as [Ir(dtbbpy)
(ppy)2][PF6] and eosin Y displayed very similar reactivity
(Table 2, entries 4 and 5).
Figure 1. Crystal structure of vinyl ether 5a. Ellipsoids are drawn at
50% probability (see the Supporting Information for details).
Intrigued by this reaction, we further investigated the action
of different noble metal catalysts on 3a (Table 1). Surprisingly,
Table 1. Rearrangement of Vinylsulfonium Ylide 3a
a
b
entry
catalyst (mol %)
yield
1
2
3
4
5
6
7
8
4 (4.1)
quant.
98 (97)
76
cd
,
4 (1.0)
PtCl2 (4.1)
PtCl4 (6.4)
PdCl2 (6.1)
Pd(ACN)2Cl2 (6.3)
CuI (5.0)
e
90
quant.
98
trace
f
92
a
Reactions were run on ca. 0.1 mmol scale under argon atmosphere.
b
c
1
Yield determined by H NMR analysis (internal standard). Isolated
d
yield in parentheses. Yield was reproducible on a 1.7 mmol scale
using 2 mol % of catalyst 4. At 180 °C, 3 h, MW irradiation. Mixture
of configurational isomers in a ratio of Z/E = 1.5:1.
e
f
very little dependence on the nature of the catalyst was
observed, and other late transition metal salts such as PdCl2,
PtCl2, or PtCl4 all catalyzed the reaction with appreciable
levels of efficiency (Table 1, entries 3−6). Conversely, CuI did
not show any catalytic activity. The observation of equally
successful reaction outcomes with π-acidic metals is informa-
tive from a mechanistic standpoint (vide infra). In 2010, we
reported a related reaction for diphenylsulfonium ylides.8a
Lowering the polarity of the solvent composition proved
to be beneficial (Table 2, entry 6). Furthermore, the reaction
time was greatly reduced when a gentle stream of oxygen was
applied (entry 7).
B
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Scheme 3. Possible Mechanistic Pathways for the Rearrangement of Vinylsulfonium Ylides: Au(I)-Catalyzed Reaction (Left)
and Thermal Reaction (Right)
a
Scheme 4. Deuterium-Labeling Experiment
a
Conditions: (a) LDA (1.1 equiv), THF, −78 °C, 15 min then D2O, 23%; (b) ethyl benzoylacetate (1.0 equiv), Tf2O (1.1 equiv), DCM, −78 °C to
rt, 12 h, 28%; (c) [JohnPhosAuACN]SbF6 (2 mol %), toluene, 70 °C, 1 h, 95%; (d) toluene, 180 °C, 3 h, MW, 88% as mixture of E/Z isomers in a
ratio of 1.4:1.
Table 2. Screening of Conditions for the Photocatalytic
Oxidation of Vinyl Ether 5a
Figure 2. Proposed transition state of the [1,4]-sigmatropic rearrange-
ment.
a
b
b
entry
catalyst
solvent
condition
time (h) yield
We then turned our attention to the generality of this
reaction, and results are summarized in Scheme 5. Halo-sub-
stituted substrate (Z)-5b reacted in similar fashion, and the
corresponding tricarbonyl compound 8b was obtained in good
yield. Subjecting the product of phenyl transposition 9a8a
to these photocatalytic conditions revealed that the reaction
was not restricted to vinyl ethers, although lower yields were
observed. Alongside the products, phenyl benzoate 10 was
isolated in 19% yield. In similar way, the methoxy-substituted
aryl ether 9b was prepared and subjected to the photocatalytic
oxidation conditions. Gratifyingly, the product was obtained in
good yield after extended reaction time, along with the oxidized
sulfoxides 11 in 8% combined yield as side products.
Surprisingly, changing what was originally the ketoester
residue from aryl to alkyl resulted in a complete change in
reaction outcome. Instead of oxidation to a tricarbonyl com-
pound, the vinyl malonate 12a, where the t-butyl substituent
has been lost, was obtained from vinyl ether (Z)-5c. A sterically
demanding environment appears to facilitate the loss of the
t-butyl moiety. In order to assess the influence of the double bond
geometry of the starting material, the two isopropyl-containing
c
1
[Ru]
[Ru]
[Ru]
[Ir]
ACN
ACN
ACN
ACN
ACN
argon
6
14
12
12
12
12
2
nr
nr
31
d
2
argon
3
4
5
6
7
open flask
open flask
open flask
open flask
O2 stream
e
58
53
f
e
eosin Y
[Ru]
5:1 CHCl3/ACN
5:1 CHCl3/ACN
57
65
[Ru]
a
All reactions carried out on a 0.01 mol scale with a concentration of
0.05 M, irradiation with blue LED (440−480 nm); yield refers to
isolated material unless stated otherwise. Catalyst loading of 3 mol %
b
unless stated otherwise; [Ru] = [Ru(bpy)3]Cl2·6H2O, [Ir] =
c
d
[Ir(dtbbpy)(ppy)2][PF6]. m-Dinitrobenzene (1.2 equiv). Diisopro-
e
pylethylamine (2 equiv). Yield determined by 1H NMR (internal
f
standard) of the crude mixture. Eosin Y (1 equiv), irradiation with
green light at 550 nm, 110 W.
isomers (Z)-5d and (E)-5d (obtained by thermal rearrange-
ment of the corresponding ylide) were separated and inde-
pendently submitted to photocatalytic oxidation. While (Z)-5d
mimics the behavior of its t-butyl analogue (Z)-5c, yielding
a vinyl ester (still carrying the isopropyl substituent and,
C
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a
Scheme 5. Scope of the Photocatalytic Oxidation
a
Reactions were carried out on a 0.05−0.15 mmol scale. All reported yields refer to isolated material: [a] α,β-diketoesters were obtained as a
mixture of diketone and hydrate in varying ratios (see Supporting Information for more information); [b] Z/E = 3.5:1, reaction was run in ACN;
[c] Z/E = 1.3:1; [d] isomers with a ratio of 1.7:1; [e] dr 1:1; [f] 70% conversion. Yield is based on unreacted starting material [g] obtained as a
single diastereomer.
Scheme 6. Photocatalytic Oxidations of Surrogate (E)-14
strikingly, as a single diastereomer 12b), the opposite isomer
gave the cyclized 1,3-dioxin-4-one 13 as major product (66%).
To gain additional insight on the mechanism of these reac-
tions, surrogate (E)-14 (Scheme 6) was synthesized according
to a literature procedure.22 Its photocatalytic oxidation pro-
duced sulfoxide ester 15 as a main product, incorporating two
additional oxygen atoms. The lower efficiency of this trans-
formation indicates a crucial role of the electron-withdrawing
functionality adjacent to the thioether of the parent compounds 5.
It is known that [Ru(bpy)3]2+ can serve as sensitizer for the
generation of singlet oxygen with very high quantum yields.23
Reactions of singlet oxygen with organic molecules have been
widely reported in the literature.24 One plausible mechanism
would be a [2 + 2] cycloaddition with the internal double bond
to yield 1,2-dioxetane 16, which could undergo ring expansion
to a endoperoxy sulfonium ylide 1825 (Scheme 7). Alter-
natively, the same intermediate could derive from an attack on
sulfur26 followed by a 5-endo-trig cyclization. These products
could also be generated by a sequential single-electron transfer.
In Scheme 8, plausible pathways from intermediate 18 to the
observed products are presented. In pathway A, generation of
an unstable epoxide25 and hydrolysis followed by elimination of
Scheme 7. Proposed Reaction with Singlet Oxygen to
Endoperoxide Sulfonium Ylide 18
sulfenic acid27 might account for the dominant formation of
diketoester 8.
The formation of sulfoxide esters 12a and 12b as well as 15
seemed to result from a 1,2-alkyl and hydride shift,28 res-
pectively (Scheme 8, pathway B). Corroborating evidence for
the proposal that the formation of 12a and 12b as well as 15
might be a concerted process is given by the fact that no vinylic
esters were isolated without concomitant oxidation to the
D
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Scheme 8. Different Pathways Depending on Substitution Pattern
Ethyl 3-Oxo-3-phenyl-2-(phenyl(vinyl)sulfanylidene)propanoate (3a):
respective sulfoxides. Additionally, the fact that 12b is
obtained as a single diastereomer could be the result of re-
stricted rotation. For the reaction of (E)-5d, the vinyl sub-
stituent and the carbonyl group of the ester seem to be in
perfect arrangement for cyclization. Even though oxygen
is not necessarily incorporated in the product, only traces
thereof are observed when the reaction is carried out in the
absence of oxygen. From common intermediate 18, a radical
cyclization with abstraction of hydrogen from thiophenol and
hydrolysis are feasible (Scheme 8, pathway C), although this
pathway could be operative starting with (E)-5d directly, as
well. The phenyl ester 10 is quite likely the retro-[2 + 2]
product of the 1,2-dioxetane intermediate 1824,29 (Scheme 8,
pathway D).
1
Brown oil (10 mmol scale, 1.120 g, 34% yield); H NMR (400 MHz,
CDCl3) δ ppm 7.70−7.63 (m, 2H), 7.55−7.48 (m, 5H), 7.45 (dd, J =
16.8, 9.0 Hz, 1H), 7.39−7.29 (m, 3H), 6.31 (dd, J = 16.8, 1.1 Hz, 1H),
6.19 (dd, J = 9.0 1.1 Hz, 1H), 3.94 (m, 2H), 0.90 (t, J = 7.1 Hz, 3H);
13C NMR (100 MHz, CDCl3) δ ppm 190.0, 166.3, 143.0, 131.6, 131.1,
131.0, 130.0, 129.5, 128.0, 127.8, 127.5, 127.1, 59.6, 14.1; HRMS
(ESI+) calcd for C19H18O3S ([M + Na]+) 349.0869, found 349.0867;
IR (neat, cm−1) 3070, 2972, 1645, 1543, 1331, 1276, 1151, 1065, 726,
696.
CONCLUSIONS
■
Ethyl 3-(4-Bromophenyl)-3-oxo-2-(phenyl(vinyl)sulfanylidene)-
propanoate (3b):
In summary, we have presented the first synthesis of a
new class of sulfonium ylides bearing a S-vinyl substituent
starting from commercially available phenyl vinylsulfoxide.
These compounds undergo an interesting stereoselective
gold-catalyzed S- to O-vinyl shift under mild conditions.
This rearrangement and its thermal variant were investigated
by deuterium-labeling experiments, supporting the interme-
diacy of five-membered cyclic intermediates. The use of a
photocatalyst in combination with oxygen and visible light
enabled the transformation of the resulting vinyl ethers into
different oxidation or cyclization products depending on the
substitution pattern. Aromatic substituents led mainly to the
formation of tricarbonyl compounds, whereas secondary or tertiary
alkyl moieties triggered a different behavior that resulted in
group migrations and fragmentations. These unusual transfor-
mations highlight the versatility and bountiful reactivity that
can be expected from modulating substitution patterns in sul-
fonium ylides.
Brown oil (5.3 mmol scale, 0.530 g, 25% yield); 1H NMR (400 MHz,
CDCl3) δ ppm 7.67−7.60 (m, 2H), 7.54−7.37 (m, 8H), 6.30 (dd, J =
16.8, 1.2 Hz, 1H), 6.19 (dd, J = 9.0, 1.2 Hz, 1H), 4.02−3.89 (m, 2H),
0.94 (t, J = 7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ ppm 188.6,
165.9, 141.7, 131.3, 131.2, 130.5, 130.0, 129.5, 127.6, 127.1, 123.7,
76.7, 59.7, 14.2; HRMS (ESI+) calcd for C19H17O3SBr ([M + Na]+)
428.9954, found 428.9961; IR (neat, cm−1) 2977, 1650, 1554, 1328,
1278, 1059, 747, 696.
Ethyl 4,4-Dimethyl-3-oxo-2-(phenyl(vinyl)sulfanylidene)-
pentanoate (3c):
EXPERIMENTAL SECTION
■
General Procedure for the Synthesis of Vinylsulfonium
Ylides. In a flame-dried flask, β-ketoester (5 mmol) and phenyl
vinylsulfoxide (0.67 mL, 5 mmol) in dry CH2Cl2 (50 mL) were
cooled to −78 °C and treated with trifluoromethanesulfonic anhy-
dride (1.11 mL, 1.86 g, 5.5 mmol). The mixture was stirred for 1 h at
this temperature before the acetone bath was removed, and the
reaction was stirred for 11 h at room temperature. It was quenched
with a saturated potassium carbonate solution (15 mL) and extracted
with CH2Cl2 three times. The combined organic layers were dried
over anhydrous sodium sulfate and concentrated in vacuo. The crude
mixture was purified by column chromatography over silica gel
(heptane/ethyl acetate = 1/1).
1
White crystals (5.1 mmol scale, 0.272 g, 18% yield); H NMR (400
MHz, CDCl3) δ ppm 7.54−7.40 (m, 5H), 7.26 (dd, J = 16.8, 9.0 Hz,
1H), 6.22 (dd, J = 16.8, 1.0 Hz, 1H), 6.11 (dd, J = 9.0, 1.0 Hz, 1H),
4.11 (q, J = 7.1 Hz, 2H), 1.32 (s, 9H), 1.18 (t, J = 7.1 Hz, 3H);
13C NMR (100 MHz, CDCl3) δ ppm 199.3, 165.3, 132.3, 130.5,
130.4, 129.7, 129.3, 126.1, 76.9, 59.4, 43.3, 27.1, 14.6; HRMS (ESI+)
calcd for C17H22O3S ([M + Na]+) 329.1182, found 329.1171;
IR (neat, cm−1) 3081, 2976, 1672, 1573, 1312, 1057, 745.
E
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Ethyl 4-Methyl-3-oxo-2-(phenyl(vinyl)sulfanylidene)pentanoate (3d):
([M + Na]+) 429.1131, found 429.1131; IR (neat, cm−1) 1665, 1323,
1249, 1055, 746.
Preparation of Phenyl-(vinyl-1-d)sulfoxide (d-1).30
To a −78 °C solution of diisoproylamine (0.85 mL, 6.06 mmol,
1.21 equiv) in 20 mL dry THF was added n-BuLi solution (15% in
hexane, 3.5 mL, 5.6 mmol, 1.12 equiv). The reaction was stirred for
30 min at this temperature, and a solution of phenyl vinylsulfoxide
(0. 67 mL, 5.01 mmol) in 10 mL of dry THF was added dropwise.
After an additional 30 min, the reaction was allowed to warm to room
temperature for 10 min. The reaction was quenched by the addition
of D2O (1 mL) and diluted with H2O (5 mL), and the organics
were extracted three times with CH2Cl2. The combined organic phases
were dried over MgSO4 and concentrated under reduced pressure.
Column chromatography over silica gel (heptane/ethyl acetate) af-
forded deuterated phenyl vinylsulfoxide in a ratio of d-1/1 = 10:1:
Brown oil (5.0 mmol scale, 0.334 g, 23% yield); 1H NMR (400 MHz,
CDCl3) δ ppm 7.51−7.41 (m, 5H), 7.32 (dd, J = 16.8, 9.1 Hz, 1H),
6.14 (dd, J = 16.8, 1.0 Hz, 1H), 6.09 (dd, J = 9.0, 1.0 Hz, 1H), 4.13
(q, J = 7.1 Hz, 2H), 3.82 (sep, J = 6.8 Hz, 1H), 1.20 (t, J = 7.1 Hz,
3H), 1.07 (dd, J = 6.8 1.4 Hz, 6H); 13C NMR (100 MHz, CDCl3)
δ ppm 198.0, 166.1, 131.8, 130.6, 130.5, 129.7, 128.4, 126.4, 75.4,
59.5, 36.1, 19.7, 19.5, 14.7; HRMS (ESI+) calcd for C16H20O3S
([M + Na]+) 315.1025, found 315.1015; IR (neat, cm−1) 3077, 2930,
1665, 1577, 1378, 1282, 1056, 746, 632.
Ethyl 3-Oxo-3-phenyl-2-(phenyl(vinyl-1-d)sulfanylidene)-
propanoate (d-3a):
1
colorless liquid (0.150 g, 20% yield); H NMR (400 MHz, CDCl3)
δ ppm 7.65−7.58 (m, 2H), 7.54−7.46 (m, 3H), 6.19 (t, J = 2.3 Hz,
1H), 5.88 (s br, 1H); 13C NMR (100 MHz, CDCl3) δ ppm 143.5,
142.9 (t, J = 27.1 Hz), 131.3, 129.6, 124.8, 120.6; HRMS (ESI+) calcd
for C8H7DOS ([M + Na]+) 176.0251, found 176.0245; IR (neat, cm−1)
1443, 1084, 1045, 750, 694.
General Procedure for the Vinyl Migration. Method A. To a
solution of vinylsulfonium ylide (1 mmol) in dry toluene (10 mL) was
added Echavarren catalyst 4 (2−5 mol %), and the reaction was heated
to 70 °C for 1 h. Removal of the volatiles in vacuo and consequent
flash chromatography over silica gel using ethyl acetate afforded vinyl
ethers.
Light brown oil (1.3 mmol scale, 0.117 g, 28% yield); 1H NMR
(400 MHz, CDCl3) δ ppm 7.69−7.61 (m, 2H), 7.55−7.47 (m, 5H),
7.37−7.29 (m, 3H), 6.30 (s, 1H), 6.19 (s, 1H), 4.00−3.87 (m, 2H),
0.89 (t, J = 7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ ppm 190.0,
166.3, 142.9, 131.5, 131.1, 130.9, 129.9, 129.5, 127.8, 127.4, 127.1,
76.5, 59.6, 14.1; HRMS (ESI+) calcd for C19H17DO3S ([M + Na]+)
350.0932, found 350.0928; IR (neat, cm−1) 3059, 2980, 1650, 1553,
1323, 1280, 1060, 725.
Method B.8a In a microwave tube, sulfonium ylide (1 mmol) was
dissolved in dry toluene (10 mL) and subjected to microwave
irradiation to 180 °C for 3 h. The bright yellow solution was concen-
trated under reduced pressure, and flash chromatography over silica
gel (heptane/ethyl acetate = 10/1) afforded the products as a mixture
of double bond isomers.
Ethyl 2-(Diphenylsulfanylidene)-3-oxo-3-phenylpropanoate (SM
of 9a):8a
Ethyl (Z)-3-Phenyl-2-(phenylthio)-3-(vinyloxy)acrylate (5a):
Pale yellow oil. Method A: 1.7 mmol scale, 0.555 g, 97% yield. Method
B: 0.1 mmol scale, 0.030 g, 92% yield as mixture of Z/E isomers in a
ratio of 1.5:1; 1H NMR (400 MHz, CDCl3) δ ppm 7.46−7.35
(m, 7H), 7.30−7.24 (m, 2H), 7.22−7.16 (m, 1H), 6.26 (dd, J = 13.7,
6.1 Hz, 1H), 4.67 (dd, J = 13.7, 2.1 Hz, 1H), 4.62 (dd, J = 6.1, 2.1 Hz,
1H), 3.81 (q, J = 7.1 Hz, 2H), 0.80 (t, J = 7.1 Hz, 3H); 13C NMR
(100 MHz, CDCl3) δ ppm 166.4, 161.1, 147.6, 135.0, 133.9, 130.2,
129.9, 129.0, 128.9, 128.6, 126.8, 112.1, 95.1, 61.4, 13.6; HRMS
(ESI+) calcd for C19H18O3S ([M + Na]+) 349.0869, found 349.0863;
IR (neat, cm−1) 3059, 2981, 1714, 1583, 1271, 1140, 1050, 741, 696.
Ethyl (Z)-3-(4-Bromophenyl)-2-(phenylthio)-3-(vinyloxy)acrylate (5b):
Diphenyl sulfoxide was used as reagent; white solid (5.2 mmol scale,
1
1.490 g, 76% yield); H NMR (400 MHz, CDCl3) δ ppm 7.75−7.67
(m, 4H), 7.58−7.45 (m, 8H), 7.38−7.28 (m, 3H), 3.91 (q, J = 7.1 Hz,
2H), 0.87 (t, J = 7.1 Hz, 3H).
Ethyl 2-(Diphenylsulfanylidene)-3-(4-methoxyphenyl)-3-oxopro-
panoate (SM of 9b):4d
The compound was prepared according to reference 4d; white solid
1
(3.1 mmol scale, 1.206 g, 95% yield); H NMR (400 MHz, CDCl3)
δ ppm 7.74−7.66 (m, 4H), 7.56 (d, J = 8.8 Hz, 2H), 7.53−7.45
(m, 6H), 6.83 (d, J = 8.8 Hz, 2H), 3.95 (q, J = 7.1 Hz, 2H), 3.82
(s, 3H), 0.94 (t, J = 7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ ppm
189.0, 166.6, 161.2, 135.4, 131.5, 130.6, 130.3, 129.9, 129.8,
112.8, 75.2, 59.6, 55.5, 14.4; HRMS (ESI+) calcd for C24H22O4S
Pale yellow solid. Method A: 1.24 mmol scale, 0.404 g, 80% yield;
1H NMR (400 MHz, CDCl3) δ ppm 7.55−7.50 (m, 2H), 7.44−7.38
(m, 2H), 7.33−7.24 (m, 4H), 7.24−7.18 (m, 1H), 6.25 (dd, J = 13.7,
6.2 Hz, 1H), 4.65 (dd, J = 13.7, 2.2 Hz, 1H), 4.29 (dd, J = 6.2,
F
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2.2 Hz, 1H), 3.83 (q, J = 7.1 Hz, 2H), 0.85 (t, J = 7.1 Hz, 3H);
13C NMR (100 MHz, CDCl3) δ ppm 166.0, 158.7, 147.6, 134.3, 132.8,
131.9, 130.4, 130.4, 129.1, 127.2, 124.6, 113.9, 95.4, 61.6, 13.7; HRMS
(ESI+) calcd for C19H17O3SBr ([M + Na]+) 428.9954, found 428.9950;
IR (neat, cm−1) 3072, 2987, 1719, 1580, 1259, 1134, 1054, 739, 689.
Ethyl (Z)-4,4-Dimethyl-2-(phenylthio)-3-(vinyloxy)pent-2-enoate (5c):
Colorless oil. Method B: 0.37 mmol, 0.129 g, 92% yield as mixture of
Z/E isomers in a ratio of 3.3:1; H NMR (400 MHz, CDCl3) δ ppm
7.92−7.57 (m, 0.6H), 7.48−7.39 (m, 4.6H), 7.34−7.15 (m, 11.2H),
7.02−6.87 (m, 3.9H), 4.06 (q, J = 7.1 Hz, 0.6H), 3.86 (q, J = 7.1 Hz,
2H), 0.99 (t, J = 7.1 Hz, 0.9H), 0.85 (t, J = 7.1 Hz, 3H).
1
Ethyl 3-(4-Methoxyphenyl)-3-phenoxy-2-(phenylthio)acrylate (9b):
Colorless oil. Method A: 0.26 mmol scale, 0.075 g, 94% yield;
1H NMR (400 MHz, CDCl3) δ ppm 7.42−7.37 (m, 2H), 7.30−7.20
(m, 3H), 6.38 (dd, J = 13.8, 6.3 Hz, 1H), 4.54 (dd, J = 13.8, 2.0 Hz,
1H), 4.23 (dd, J = 6.3, 2.0 Hz, 1H), 3.91 (q, J = 7.2 Hz, 2H), 1.22
(s, 9H), 1.06 (t, J = 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ ppm
166.3, 164.3, 151.2, 133.3, 131.7, 128.8, 127.6, 114.6, 90.9, 61.4, 39.6,
28.4, 13.8; HRMS (ESI+) calcd for C17H22O3S ([M + Na]+) 329.1182,
found 329.1182; IR (neat, cm−1) 2963, 2871, 1721, 1633, 1585, 1239,
1151, 1043, 740, 690.
Yellow solid. Method B: 0.98 mmol scale, 0.380 g, 95% yield as
mixture of Z/E isomers in a ratio of 1.33:1. Z-Isomer: 1H NMR
(400 MHz, CDCl3) δ ppm 7.59−7.53 (d, J = 9 Hz, 2H), 7.45−7.35
(m, 2H), 7.34−7.14 (m, 5H), 7.01−6.86 (m, 3H), 6.81−6.74 (m, 2H),
3.90 (q, J = 7.1 Hz, 2H), 3.76 (s, 3H), 0.90 (t, J = 7.1 Hz, 3H);
13C NMR (100 MHz, CDCl3) δ ppm 166.8, 160.9, 158.9, 156.2, 134.5,
130.5, 129.6, 129.2, 129.0, 127.0, 126.3, 123.0, 117.9, 114.9, 113.9,
61.5, 55.4, 13.8. E-isomer: 1H NMR (400 MHz, CDCl3) δ ppm 7.45−
7.35 (m, 4H), 7.34−7.14 (m, 5H), 7.01−6.86 (m, 3H), 6.81−6.74
(m, 2H), 4.06 (q, J = 7.1 Hz, 2H), 3.75 (s, 3H), 0.98 (t, J = 7.1 Hz,
3H); 13C NMR (100 MHz, CDCl3) δ ppm 166.6, 161.0, 160.8,
156.6, 136.1, 131.6, 130.5, 129.5, 128.0, 126.4, 124.8, 122.9, 118.1,
114.9, 113.6, 61.5, 55.3, 14.0; HRMS (ESI+) calcd for C24H22O4S
([M + Na]+) 429.1131, found 429.1134; IR (neat, cm−1) 1713, 1249,
1198, 1174, 1044, 1026, 740.
Ethyl (Z)-4-Methyl-2-(phenylthio)-3-(vinyloxy)pent-2-enoate ((Z)-5d):
Ethyl (Z)-3-Phenyl-2-(phenylthio)-3-((vinyl-1-d)oxy)acrylate (d-5a):
Colorless oil. Method A: 0.1 mmol scale, 0.026 g, 91% yield. Method
B: 0.54 mmol scale, 0.120 g, 76% yield as mixture of Z/E isomers in a
ratio of 1.6:1; 1H NMR (400 MHz, CDCl3) δ ppm 7.29−7.23
(m, 4H), 7.20−7.14 (m, 1H), 6.43 (dd, J = 13.8, 6.1 Hz, 1H),
4.57 (dd, J = 13.8, 2.1 Hz, 1H), 4.26 (dd, J = 6.1, 2.1 Hz, 1H),
4.05 (q, J = 7.1 Hz, 2H), 3.34 (sep, J = 6.8 Hz, 1H), 1.18 (d, J =
6.8 Hz, 6H), 1.04 (t, J = 7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3)
δ ppm 172.1, 166.6, 150.6, 135.7, 129.0, 128.5, 126.4, 111.1, 92.0, 61.6,
33.2, 19.9, 13.9; HRMS (ESI+) calcd for C16H20O3S ([M + Na]+)
315.1025, found 315.1010; IR (neat, cm−1) 2972, 2874, 1708, 1635,
1583, 1231, 1144, 1052, 740, 691.
Pale yellow oil. Method A: 0.09 mmol scale, 0.029 g, 95% yield.
Method B: 0.04 mmol scale, 88% yield (1H NMR) as mixture of E:Z
isomers in a ratio of 1.4:1; 1H NMR (400 MHz, CDCl3) δ ppm 7.46−
7.35 (m, 7H), 7.30−7.24 (m, 2H), 7.22−7.16 (m, 1H), 4.66 (q, J = 1.9
Hz, 1H), 4.26 (d, J = 1.9 Hz, 1H), 3.81 (q, J = 7.1 Hz, 2H), 0.80 (t, J =
7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ ppm 166.4, 161.0, 147.4
(t, J = 28.4 Hz), 134.9, 133.8, 130.2, 129.9, 129.0, 128.9, 128.6, 126.8,
112.1, 94.9, 61.3, 13.6; HRMS (ESI+) calcd for C19H17DO3S ([M +
Na]+) 350.0932, found 350.0927; IR (neat, cm−1) 3058, 2980, 1716,
1584, 1149, 1056, 740, 697.
Ethyl (E)-4-Methyl-2-(phenylthio)-3-(vinyloxy)pent-2-enoate ((E)-5d):
General Procedure for the Photocatalytic Oxidation. In a
glass vial, the respective substrate (0.05−0.15 mmol) was dissolved in
CHCl3/ACN 4:1 (0.05 M), treated with [Ru(bipy)3]Cl2·6H2O (2 mol
%), irradiated with a blue LED light bulb (8 W), and stirred without a
lid for 12 h. Water was added (2 mL), and the reaction was extracted
twice with CH2Cl2. Drying over anhydrous sodium sulfate and removal
of the solvent under reduced pressure afforded crude product which
was purified by column chromatography over silica gel (heptane/ethyl
acetate = 5/1).
Obtained by chromatographic separation. Method B: 0.54 mmol scale,
0.045 g, 29% yield, 76% yield as mixture of Z/E isomers in a ratio
1
of 1.6:1; H NMR (400 MHz, CDCl3) δ ppm 7.32−7.23 (m, 4H),
7.19−7.14 (m, 1H), 6.30 (dd, J = 13.7, 6.1 Hz, 1H), 4.67 (dd, J =
13.7, 2.1 Hz, 1H), 4.30 (dd, J = 6.1, 2.1 Hz, 1H), 4.08 (q, J = 7.1 Hz,
2H), 3.59 (sep, J = 6.8 Hz, 1H), 1.13 (d, J = 6.8 Hz, 6H), 1.11 (t, J =
7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ ppm 172.6, 166.1, 150.4,
135.9, 129.1, 127.8, 126.3, 108.3, 93.4, 61.5, 32.3, 19.7, 14.1; HRMS
(ESI+) calcd for C16H20O3S ([M + Na]+) 315.1025, found 315.1010.
Ethyl 3-Phenoxy-3-phenyl-2-(phenylthio)acrylate (9a):8a
Ethyl 2,3-Dioxo-3-phenylpropanoate (8a):31
Yellow oil. From 5a: 0.082 mmol scale, 0.011 g, 65% yield. From 9a:
0.080 mmol scale, 0.007 g, 43% yield (reaction performed in 100%
ACN); mixture of hydrate and keto form in a ratio of 5.3:1. Hydrate:
1H NMR (400 MHz, CDCl3) δ ppm 8.07 (d, J = 8.2 Hz, 2H), 7.65−
7.61 (m, 1H), 7.50−7.45 (m, 2H), 5.28 (s br, 2H), 4.22 (q, J = 7.1 Hz, 2H),
G
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1.08 (t, J = 7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ ppm 191.7,
170.0, 134.7, 131.5, 130.3, 128.9, 91.7, 63.3, 13.7. Ketone: H NMR
Yellow oil. From 5c: 0.14 mmol scale, 0.030 g, 79% yield; mixture of
diastereomers in a ratio of 1:1; H NMR (600 MHz, CDCl3) δ ppm
1
1
7.78−7.72 (m, 4H), 7.58−7.51 (m, 6H), 7.25 (dd, J = 13.8, 6.2 Hz,
1H), 6.99 (dd, J = 13.8, 6.2 Hz, 1H), 4.98 (dd, J = 13.8, 2.1 Hz, 1H),
4.84 (dd, J = 13.8, 2.1 Hz, 1H), 4.71 (dd, J = 6.2, 2.1 Hz, 1H), 4.62
(dd, J = 6.2, 2.1 Hz, 1H), 4.51 + 4.51 (2 s, 2H), 4.32 (q, J = 7.1 Hz,
2H), 4.06 (m, 2H), 1.31 (t, J = 7.1 Hz, 3H), 1.13 (t, J = 7.1 Hz, 3H);
13C NMR (150 MHz, CDCl3) δ ppm 162.4, 161.9, 160.1, 159.5, 141.2,
141.1, 141.0, 140.6, 132.7, 132.7, 129.5, 129.4, 125.5, 125.4, 100.2
(2C), 75.9, 75.8, 63.4, 63.1, 14.1, 13.9; HRMS (ESI+) calcd for
C13H14O5S ([M + Na]+) 305.0454, found 305.0451; HRMS (ESI−)
calcd for C13H14O5S ([M − H+]−) 281.0489, found 281.0490.
1-Ethyl 3-Vinyl-2-isopropyl-2-(phenylsulfinyl)malonate (12b):
(400 MHz, CDCl3) δ ppm 8.00 (d, J = 8.0 Hz, 2H), 7.73−7.69
(m, 1H), 7.57−7.53 (m, 2H), 4.43 (q, J = 7.2 Hz, 2H), 1.39 (t, J =
7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ ppm 190.3, 183.9,
160.7, 135.6, 131.7, 130.1, 129.3, 63.4, 14.1; HRMS (ESI+) calcd for
C11H10O4 ([M + MeOH + Na]+) 261.0733, found 261.0721; IR (neat,
cm−1) 3062, 2934, 1736, 1690, 1237, 1131, 718.
Ethyl 3-(4-Bromophenyl)-2,2-dihydroxy-3-oxopropanoate (8b):
White crystals. From 5b: 0.222 mmol scale, 0.050 g, 79% yield;
mixture of hydrate and keto form in a ratio of 2.1:1. Hydrate: 1H NMR
(400 MHz, CDCl3) δ ppm 7.94 (d, J = 8.8 Hz, 2H), 7.62 (d, J =
8.8 Hz, 2H), 5.23 (s br, 2H), 4.22 (q, J = 7.1 Hz, 2H), 1.12 (t, J =
7.1 Hz, 3H); 13C NMR (150 MHz, CDCl3) δ ppm 190.9, 169.8, 132.4,
1
131.7, 130.4, 130.3, 91.7, 63.6, 13.9. Ketone: H NMR (400 MHz,
Colorless oil. From (Z)-5d: 0.1 mmol scale, 0.017 g, 53% yield; single
diastereomer; 1H NMR (400 MHz, CDCl3) δ ppm 7.80−7.74
(m, 2H), 7.51−7.44 (m, 3H), 7.27 (dd, J = 13.9, 6.2 Hz, 1H), 5.00
(dd, J = 13.9, 2.0 Hz, 1H), 4.73 (dd, J = 6.2, 2.0 Hz, 1H), 3.84 (dq, J =
10.7, 7.1 Hz, 1H), 3.47 (dq, J = 10.7, 7.1 Hz, 1H), 2.95 (sep, J =
6.9 Hz, 1H), 1.25 (dd, J = 10.2, 6.9 Hz, 6H), 0.92 (t, J = 7.1 Hz, 3H);
13C NMR (100 MHz, CDCl3) δ ppm 164.6, 163.3, 141.1, 140.6, 131.8,
128.7, 126.5, 99.9, 83.7, 61.8, 29.9, 19.3, 17.7, 13.7; HRMS (ESI+)
calcd for C16H20O5S ([M + Na]+) 347.0924, found 347.0925; IR
(neat, cm−1) 2977, 1724, 1241, 1140, 1084, 751, 595.
CDCl3) δ ppm 7.88 (d, J = 8.8 Hz, 2H), 7.70 (d, J = 8.8 Hz, 2H), 4.43
(q, J = 7.1 Hz, 2H), 1.40 (t, J = 7.1 Hz, 3H); 13C NMR (150 MHz,
CDCl3) δ ppm 189.1, 183.3, 160.7, 132.8, 131.5, 131.5, 130.4,
63.6, 14.1;HRMS (ESI+) calcd for C11H9O4Br ([M + Na]+) 306.9576,
found 306.9569; IR (neat, cm−1) 2983, 1737, 1585, 1238, 1141,
1010, 751.
Ethyl 3-(4-Methoxyphenyl)-2,3-dioxopropanoate (8c):31
6-Isopropyl-2-methyl-5-(phenylthio)-4H-1,3-dioxin-4-one (13):
Pale yellow oil. From 9b: 0.12 mmol scale, 0.024 g, 83% yield; mixture
of hydrate and ketoform in a ratio of 2.1:1. Hydrate: 1H NMR
(400 MHz, CDCl3) δ ppm 8.06 (d, J = 9.0 Hz, 2H), 6.94 (d, J = 9.0
Hz, 2H), 5.29 (s, 2H), 4.22 (q, J = 7.1 Hz, 2H), 3.89 (s, 3H), 1.12
(t, J = 7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ ppm 189.9, 170.4,
1
164.9, 132.9, 124.3, 114.2, 91.6, 63.3, 55.7, 13.9. Ketone: H NMR
1
(400 MHz, CDCl3) δ ppm 8.00 (d, J = 8.9 Hz, 2H), 7.01 (d, J =
8.9 Hz, 2H), 4.42 (q, J = 7.2 Hz, 2H), 3.91 (s, 3H), 1.39 (t, J = 7.2 Hz,
3H); 13C NMR (150 MHz, CDCl3) δ ppm 188.4, 184.1, 165.7, 161.1,
132.8, 124.8, 114.7, 63.3, 55.9, 14.1; HRMS (ESI+) calcd for C12H12O5
([M + Na + MeOH]+) 291.0839, found 291.0843; IR (neat, cm−1)
3410 (br), 1740, 1679, 1598, 1247, 1093, 848.
Colorless oil. From (E)-5d: 0.05 mmol, 0.009 g, 66% yield; H NMR
(400 MHz, CDCl3) δ ppm 7.30−7.20 (m, 5H), 7.19−7.12 (m, 1H),
5.67 (q, J = 5.2 Hz, 1H), 3.60 (sep, J = 6.9 Hz, 1H), 1.73 (d, J = 5.2
Hz, 3H), 1.13 (dd, J = 6.8, 5.5 Hz, 6H); 13C NMR (100 MHz, CDCl3)
δ ppm 185.0, 161.8, 136.2, 129.2, 127.1, 126.2, 99.0, 98.4, 31.3, 19.9,
19.5, 19.0; HRMS (ESI+) calcd for C14H16O3S ([M + Na]+) 287.0718,
found 287.0713; IR (neat, cm−1) 2975, 1741, 1566, 1327, 1113, 1022, 740.
Ethyl 3-(4-Methoxyphenyl)-3-phenoxy-2-(phenylsulfinyl)acrylate (11):
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.joc.6b01073.
■
S
X-ray analysis and NMR spectra (PDF)
X-ray data (CIF)
Pale yellow oil. From 9b: 0.12 mmol scale, 0.004 g, 8% yield; mixture
of isomers in a ratio of 1.7:1; H NMR (400 MHz, CDCl3) δ ppm
AUTHOR INFORMATION
Corresponding Author
*E-mail: nuno.maulide@univie.ac.at.
Notes
■
1
7.79−7.72 (m, 1.7H), 7.67−7.58 (m, 2.2H), 7.52−7.38 (m, 6.6H),
7.25−7.15 (m, 3.1H), 7.04−6.86 (m, 6.0H), 6.76 (d, J = 8.8 Hz, 2.1H),
4.04−3.86 (m, 3.2H), 3.80 (s, 1.7H), 3.74 (s, 3.0H), 0.91−1.00
(m, 4.7H); HRMS (ESI+) calcd for C24H22O5S ([M + Na]+)
445.1080, found 445.1083.
The authors declare no competing financial interest.
1-Ethyl 3-Vinyl-2-(phenylsulfinyl)malonate (12a):
ACKNOWLEDGMENTS
■
We acknowledge the generous support of our research by the
University of Vienna, the ERC (StG 278872), and the DFG
(Grants MA 4861/4-1 and 4-2). Ing. A. Roller (U. Vienna) is
acknowledged for assistance with crystallographic structure
determination.
H
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́
(c) Eberhart, J.; Shrives, H.; Alvarez, A.; Carrer, A.; Zhang, Y.;
̈
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