Catalysis of intramolecular Morita-Baylis-Hillman and Rauhut-Currier reactions by fluorous phosphines; facile recovery by liquid/solid organic/fluorous biphase protocols involving precipitation, teflon tape, and Gore-Rastex fiber

Article abstract of DOI:10.1002/adsc.200800403

The fluorous phosphine P[(CH₂)₃R_f8] ₃ [1, R_f8=(CF₂)₇CF₃; 10 mol%] catalyzes intramolecular Morita-Baylis-Hillman reactions of O=CH-(CH ₂)_nCH=CH(C=O)R [n/R=2/Ph (2a), 2/S-i-Pr, 3/p-tol] in acetonitrile at 60-72°C. Upon cooling, 1 precipitates and is recycled. The products HOCH(CH₂)_nCH=C(C=O)R are isolated from the supernatant (78-96%). The educt i-PrS(C=O)CH=CH(CH₂) ₂CH=CH(C=O)S-i-Pr similarly undergoes a Rauhut-Currier reaction to give i-PrS(C=O)CH₂CH(CH₂)₂CH=C(C=O)S-i-Pr (71-73%). In the case of 2a, reactions are also conducted in the presence of Teflon tape or Gore-Rastex fiber. The catalyst now precipitates onto the fluoropolymer support, mechanically facilitating recycling. For each reaction, three to five cycles are conducted. HPLC or GC monitoring of the rates show low activity losses, with Gore-Rastex fiber giving better results than Teflon tape, presumably due to a higher surface area.

Full text of DOI:10.1002/adsc.200800403

UPDATES
DOI: 10.1002/adsc.200800403
Catalysis of Intramolecular Morita–Baylis–Hillman and Rauhut–
Currier Reactions by Fluorous Phosphines; Facile Recovery by
Liquid/Solid Organic/Fluorous Biphase Protocols Involving
Precipitation, Teflonꢀ Tape, and Gore-Rastexꢀ Fiber
Florian O. Seidela and John A. Gladysza,b,*
a
Institut für Organische Chemie and Interdisciplinary Center for Molecular Materials, Friedrich-Alexander-Universität
Erlangen-Nürnberg, Henkestraße 42, 91054 Erlangen, Germany
Department of Chemistry, Texas A&M University, PO Box 30012, College Station, Texas 77842-3012, USA
b
Fax : (+1)-979-845-5629; e-mail: gladysz@mail.chem.tamu.edu
Received: June 28, 2008; Published online: September 26, 2008
Abstract: The fluorous phosphine P
Rf8 =(CF2)7CF3; 10 mol%] catalyzes intramolecular
Morita–Baylis–Hillman reactions of O=CH-
G
pounds have little or no solubility. In subsequent re-
finements, the lengths of the Rfn segments were used
to modulate catalyst solubilities in organic solvents,
such that homogeneous conditions could be achieved
at elevated temperatures, with near quantitative cata-
lyst precipitation at room temperature or below.[3,4]
We then introduced the concurrent use of solid fluo-
ropolymer supports, providing a locus for deposi-
tion.[3,5] In conceptually related recycling efforts,
others have applied fluorous silica gel.[6–10]
A
N
p-tol] in acetonitrile at 60–728C. Upon cooling, 1
precipitates and is recycled. The products HOCK H-
(CH2)nCH=CL
natant (78–96%). The educt i-PrS
(CH2)2CH=CH(C=O)S-i-Pr similarly undergoes a
Rauhut–Currier reaction to give i-PrS(C=
O)CH2CK H(CH2)2CH=CL (C=O)S-i-Pr (71–73%). In
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A
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N
In two feasibility studies, we described (1) the use
the case of 2a, reactions are also conducted in the
presence of Teflonꢀ tape or Gore-Rastexꢀ fiber.
The catalyst now precipitates onto the fluoropoly-
mer support, mechanically facilitating recycling. For
each reaction, three to five cycles are conducted.
HPLC or GC monitoring of the rates show low ac-
tivity losses, with Gore-Rastexꢀ fiber giving better
results than Teflonꢀ tape, presumably due to a
higher surface area.
of Teflonꢀ shavings as a mechanical support for recy-
cling the fluorous phosphine P[(CH2)2Rf8]3, which is
G
an effective Lewis base or nucleophilic catalyst for ad-
ditions of alcohols to propiolate esters (n-octane,
658C),[3] and (2) the use of Teflonꢀ tape as an adsorb-
ent for recycling a rhodium hydrosilylation catalyst
derived from ClRh{P[(CH2)2Rf6]3}3 (dibutyl ether,
T
558C).[5] We were naturally interested in broadening
the applicability of these protocols, and evaluating a
wider range of fluoropolymer supports.
Earlier, we noted that the phosphine P[(CH2)3Rf8]3
A
Keywords: fluorous phase; Morita–Baylis–Hillman
reaction; organocatalysis; phosphines; Rauhut–Cur-
rier reaction; recycling
(1),[11] which contains an additional methylene spacer
between the phosphorus atom and the Rf8 segments,
is a much stronger Lewis base and more active cata-
lyst for alcohol additions to propiolates.[3,12] Accord-
ingly, we sought to examine its efficacy with and re-
coverability from other types of reactions catalyzed
by phosphorus Lewis bases.[13–17] Thus, intramolecular
Morita–Baylis–Hillman and Rauhut–Currier reactions
Introduction
Among the many methods for catalyst recovery and of olefinic dicarbonyl compounds were selected for
recycling, those involving fluorous systems continue investigation. Such transformations have been previ-
[1]
to developand evolve.
This now familiar approach ously studied by several groups,[16,17] and in separate
utilizes “ponytails” or phase tags such as (CH2)mRfn efforts we have developed chiral rhenium-containing
[Rfn =(CF2)nÀ1CF3] to render catalysts fluorophilic, en- phosphorus Lewis base catalysts that effect enantiose-
abling their recovery in orthogonal fluorous phases. lective cyclizations.[14]
The initial applications of this technique utilized per-
fluoroalkane solvents,[2] in which most organic com-
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Florian O. Seidel and John A. Gladysz
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Results and Discussion
For screening purposes, the aldehydic a,b-unsaturated
ketone O=CH
N
N
chosen. As shown in Figure 1, A, 1 (10 mol%) and a
0.0500M CH3CN solution of 2a (2.00 mL) were com-
bined in a vial under argon. Catalyst 1 did not seem
to dissolve.[18] The mixture was heated at 60–648C
(sand bath) and appeared to become homogeneous
(0.0050M in 1). Aliquots were assayed by HPLC.[19]
The previously reported intramolecular Morita–
Baylis–Hillman product 2b gradually formed, reach-
ing 81% yield after 9 h and 85% yield after 24 h. The
mixture was cooled to room temperature (3 h) and
then À308C (overnight). Catalyst 1 precipitated,
mostly on the sides of the vial. The product solution
was carefully removed by syringe and evaporated to
1
dryness. A H NMR spectrum of the residue (CDCl3)
indicated an 85% yield of 2b, as assayed by integra-
tion of the signals at d=6.68 and 5.30 versus the total
phenyl signals.
The vial containing precipitated 1 was washed with
CH3CN and dried under vacuum (see Figure 2, A),
and then charged with 1.92 mL of a 0.0500M solution
of 2a in CH3CN as above. Four additional cycles were
conducted, each with 0.080 mL less of the 0.0500M
solution than the previous cycle (1.84, 1.76, 1.68 mL)
to exactly compensate for the catalyst removed in the
aliquots. The data in Figure 1, A indicate an excellent
retention of activity. After the fifth cycle, the catalyst
1
residue was dissolved in CF3C6H5, and analyzed by H
and 31P NMR. This showed a 76:24 ratio of 1 and the
corresponding phosphine oxide O=P[(CH2)3Rf8]3 (ca.
G
2% in parallel experiments analyzed after the first
cycle).[11,20] Control experiments established that the
oxide, which was independently synthesized, is not an
active catalyst under similar conditions.
The preceding sequence was repeated in the pres-
ence of fluoropolymer supports. The first experiments
utilized 0.160 g segments (ca. 550”12 mm) of Teflonꢀ
tape (Figure 2, B and C). After each cycle, the tape
was removed, washed with CH3CN (4”1.5 mL), and
dried under vacuum (Figure 2, D). After the fifth
cycle, the catalyst residue was dissolved in CF3C6H5.
Figure 1. Yield of 2b as a function of cycle: A (top), catalyst
recovery via precipitation; B (middle), catalyst recovery via
precipitation onto Teflonꢀ tape; C (bottom), catalyst recov-
ery via precipitation onto Gore-Rastexꢀ fiber.
1
Analysis by H and 31P NMR indicated a 75:25 ratio
of 1 and the corresponding oxide. As shown in
Figure 1, B, the yield of 2b after the first cycle was with the retention of activity over the first four cycles
quite close to that in Figure 1, A (82 vs. 85%), but ac- very close to that achieved with precipitation alone.
1
tivity was not as well maintained in subsequent cycles. After the final cycle, H and 31P NMR analyses indi-
Possible rationales are offered below.
cated a 63:37 ratio of 1 and the corresponding oxide.
Next, an analogous sequence was conducted in the
The generality of the protocol in Figure 1, A was
presence of a plug of Gore-Rastexꢀ fiber (0.160 g),[21] tested with additional substrates. As shown in
as illustrated in Figure 2, E–G. This material can be Figure 3, the aldehydic a,b-unsaturated thioester and
viewed as a porous modification of Teflonꢀ, consistent ketone O=CH
A
(C=O)S-i-Pr (3a)[14] and
with the “breathable” nature of commercial outdoor O=CH
A
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garments based upon it. The data in Figure 1, C show converted to the five- and six-membered carbocycles
a tangible improvement over those with Teflonꢀ tape, 3b and 4b at 60–648C and 70–728C, respectively. The
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Catalysis of Intramolecular Morita–Baylis–Hillman and Rauhut–Currier Reactions
UPDATES
Figure 2. Photographs representative of the recycling sequences in Figure 1. A (Figure 1, A). Precipitate prior to start of
cycle 2. B (Figure 1, B). Reaction mixture and Teflonꢀ tape prior to the start of cycle 1. C (Figure 1, B). Reaction mixture
after cycle 1. D (Figure 1, B). Catalyst coated Teflonꢀ tape prior to adding the reaction mixture for cycle 2. E (Figure 1, C).
Reaction mixture and Gore-Rastexꢀ fiber prior to the start of cycle 1. F (Figure 1, C). Reaction mixture after cycle 1. G
(Figure 1, C). Catalyst coated Gore-Rastexꢀ fiber prior to adding the reaction mixture for cycle 2.
former reaction was monitored by GC versus an inter- by-products formed. In any event, the retention of ac-
nal standard; the latter was monitored by HPLC as tivity was excellent. All of the cyclized products were
above. The yields of 3b ranged from 95–96% at the purified by column chromatography, and character-
end of each cycle, and those of 4b from 79–81%. In ized by NMR (1H, 13C) and IR spectroscopy as sum-
both cases there was good retention of activity, al- marized in the experimental section. For 3b–5b, which
though the shape of the plot for the final cycle with have not been reported outside of our research group,
4b suggests 1–2 measurement artifacts.
elemental analyses are also given.
Finally, the protocol in Figure 1, A was extended to
Importantly, two other groups have developed fluo-
the
bis(thioester)
i-PrS(CO)CH=CH(CH2)2CH= rous catalyst systems for intermolecular (aza)-Morita–
N
CH(CO)S-i-Pr (5a),[14] which is capable of a vinylo- Baylis–Hillman reactions.[22,23] One family (I) features
gous version of the preceding transformations, the a chiral phosphorus Lewis base. Although high ee
Rauhut–Currier reaction. GC analyses showed the values have been reported, no recycling has to our
formation of the cyclic dicarbonyl compound 5b, with knowledge been carried out. The other (II) features a
yields of 71–73% at the end of each cycle (Figure 3, fluorous ytterbium Lewis acid that is used in conjunc-
bottom). The starting 5a was consumed, and several tion with a stoichiometric amount of a fluorous pyri-
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Florian O. Seidel and John A. Gladysz
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dine. This system could be recycled with particularly
high efficiency.
Conclusions
In summary, the above experiments provide addition-
al examples of the facile and efficient recovery of
thermomorphic fluorous catalysts by precipitation
from organic solvents. They also significantly extend
the number of catalyst systems demonstrated to be re-
cyclable by precipitation onto Teflonꢀ tape,[5,24] and
provide the first use of Gore-Rastexꢀ fiber for recov-
ery. The latter fluoropolymer gives slightly better re-
sults, consistent with a greater surface area. Although
recycling via unassisted precipitation appears to be
most efficient, there is an obvious mechanical conven-
ience in simply being able to “fish out” a catalyst and
immediately apply it again. We speculate that the
higher catalyst loading associated with these reactions,
as opposed to the rhodium systems reported earlier
(10 mol% vs. 0.15 mol%),[5] may “saturate” the poly-
mer surface, leading to small losses in the washing
steps. Efforts to clarify these points, as well as addi-
tional examples of all of the preceding types of proto-
cols, will be described in forthcoming publications.[25]
Experimental Section
General Data
NMR spectra were recorded on Bruker 300 MHz or
400 MHz spectrometers at ambient probe temperature
(278C) and referenced to the residual solvent signal (1H:
CHCl3, 7.26 ppm; 13C: CDCl3, 77.0 ppm). IR spectra were
recorded on an ASI React IRꢀ-1000 spectrometer. HPLC
analyses were conducted with a ThermoQuest instrument
package
(pump/autosampler/detector
P4000/AS3000/
UV6000 LP; Column: Macherey–Nagel, Nucleosil 100–5).
GC analyses were conducted with a ThermoQuest TRACE
GC 2000 instrument with FID and an Optima-5–0.25 mm ca-
pillary column. Column chromatography was conducted
using silica gel 60M (Macherey–Nagel). The Gore-Rastexꢀ
fiber (30 den) was obtained as a sample from Gore corpora-
tion
(http://www.gore.com/en_xx/products/fabrics/sewing/
rastex_weave_datasheet.html).
Chemicals were treated as follows: CH3CN and CH2Cl2,
distilled from CaH2 under N2, with CH3CN for catalysis fur-
thermore freeze-pump-thaw degassed (3”); CF3C6H5
freeze-pump-thaw degassed (3”); ethyl acetate and pentane
for column chromatography, distilled and stored over molec-
ular sieves; isopropyl alcohol (Roth) and hexanes (Fischer)
for HPLC, and CDCl3 (99.8%, Deutero GmbH), used as re-
ceived.
Figure 3. Yields of 3b, 4b, and 5b as a function of cycle, with
catalyst recovery via precipitation.
Recycling Sequence A (Figure 1, A)
A vial was charged with O=CHCH2CH2CH=CH
C
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Catalysis of Intramolecular Morita–Baylis–Hillman and Rauhut–Currier Reactions
UPDATES
10À2 mbar), filled with N2, and transferred into an argon
glove box. The vial was further charged with P[(CH2)3Rf8]3
HOCHCHH’, 1H), 2.56–2.48 (m, HOCHCHH’, 1H), 2.40–
2.31 (m, CHH’CH=C, 1H), 1.97–1.89 (m, CHH’CH=C, 1H);
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(1;[11] 0.0141 g, 0.010 mmol) and CH3CN (2.00 mL) to give a
0.0500M solution of 2a. The mixture was heated at 60–648C
(sand bath) with stirring. Aliquots were periodically re-
moved (0.010 mL), diluted with CH3CN (1.50 mL) and ana-
lyzed by HPLC (98:2 v/v hexanes/isopropyl alcohol, flow=
0.5 mLminÀ1, 270 nm, SiO2). After 24 h, the mixture was
cooled to room temperature (3 h) and then À308C (over-
night). The supernatant was carefully separated from the
precipitated 1 by syringe, taken to dryness, and dissolved in
13C{1H} NMR (101 MHz, CDCl3): d=194.9 [s, CH=C
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O)], 149.0 [s, CH=C
A
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(s, i-Ph), 132.4 (s, p-Ph), 128.9, 128.3 (2s, o-, m-Ph), 76.5 (s,
HOCH), 31.7, 31.3 (2s, 2 CH2); IR (thin film): n=3450 (br,
nOH), 1633 (s, nC O), 1598 cmÀ1 (s, nC C).
=
=
HOCK H(CH2)2CH=CL (C=O)S-i-Pr (3b) was obtained (3:2
U
v/v ethyl acetate/pentane) as a colorless oil. Anal. calcd.
(%) for C9H14O2S (186.1): C 58.03, H 7.58, S 17.21; found: C
1
57.63, H 7.71, S 16.78; H NMR (400 MHz, CDCl3): d=6.89
1
3
CDCl3. A H NMR spectrum was recorded. The yield of 2b
(dd, JH,H =2.8 Hz and 2.8 Hz, CHH’CH=C, 1H), 5.16–5.13
3
was calculated by integration of the signals at d=6.68 and
(m, HOCH, 1H), 3.74 [sept, JH,H =7.2 Hz, CH
A
5.30 versus all phenyl signals.
2.78 (br s, HO, 1H), 2.73–2.62 (m, HOCHCHH’, 1H), 2.46–
2.27 (m, CHH’CH=C, HOCHCHH’, 2H), 1.91–1.82 (m,
The precipitated 1 was washed with CH3CN (0.5 mL) and
dried under oil pump vacuum. The vial was recharged with
a 0.0500M CH3CN solution of 2a (1.92 mL) and the above
procedure repeated. The volume was decreased by 0.080 mL
for each cycle to compensate for the catalyst lost in the ali-
quots. After the final cycle, the catalyst was washed with
CH3CN (0.5 mL), dried under oil pump vacuum, and dis-
CHH’CH=C, 1H), 1.39 [d, CH
13C{1H} NMR (101 MHz, CDCl3): d=190.1 [s, CH=C
O)], 145.2 [s, CH=C(C=O)], 144.4 [s, CH=C(C=O)], 75.7 (s,
HOCH), 34.3 [s, CH(CH3)2], 31.8 (s, HOCHCH2), 30.9 (s,
CH2CH=C), 23.0 [s, CH(CH3)2]; IR (thin film): n=3450 (br,
A
A
A
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nOH), 1648 (s, nC O), 1613 cmÀ1 (s, nC C).
=
=
solved in degassed CF3C6H5. Then 31P and H NMR spectra
were recorded (data: see text).
HOCK H(CH2)3CH=CL (C=O)-p-tol (4b) was obtained (4:1
R
1
v/v ethyl acetate/pentane) as a pale yellow oil. Anal. calcd.
(%) for C14H16O2 (216.1): C 77.75, H 7.46; found: C 77.18,
3
H 7.53; 1H NMR (400 MHz, CDCl33): d=7.58 (d, JH,H
=
Recycling Sequence B (Figure 1, B)
8.2 Hz, C6H4, o to C=O, 2H), 7.24 (d, JH,H =8.2 Hz, C6H4, m
to C=O, 2H), 6.70 (t, JH,H =3.9 Hz, CH=C, 1H), 4.72–4.69
3
A vial was charged with 2a (0.0188 g, 0.100 mmol), evacuat-
ed (1 h, 1”10À2 mbar), filled with N2, and transferred into
an argon glove box. The vial was further charged with 1
(0.0141 g, 0.010 mmol), Teflonꢀ tape (0.160 g, ca. 550”
12 mm) and CH3CN (2.00 mL) to give a 0.0500M solution
of 2a. The mixture was heated at 60–648C (sand bath) with
stirring. Aliquots were periodically analyzed per sequence
A. After 24 h, the mixture was cooled to room temperature
(3 h) and then À308C (overnight). The supernatant was
carefully separated from the coated Teflonꢀ tape by syringe,
taken to dryness, and analyzed per sequence A.
(m, HOCH, 1H), 3.55 (br s, HO, 1H), 2.41 (s, CH3, 3H),
2.42–2.18, 1.97–1.82, 1.69–1.60 (3m, 3 CHH’, 6H); 13C{1H}
NMR (101 MHz, CDCl3): d=199.1 [s, CH=C
(s, C6H4, p to C=O), 142.7 [s, CH=C(C=O)], 139.9 [s, CH=C-
(C=O)], 135.0 (s, C6H4, i to C=O), 129.6, 128.9 (2s, C6H4, o,
A
AHCTREUNG
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m to C=O), 64.2 (s, HOCH), 21.6 (s, CH3), 29.7, 26.3, 17.5
(3s, 3 CH2); IR (thin film): n=3460 (br, nOH), 1633 (s, nC O),
=
1606 cmÀ1 (s, nC C).
=
i-PrS
N
N
tained (1:9 v/v ethyl acetate/pentane) as a tan liquid. Anal.
calcd. (%) for C14H22O2S2 (286.1): C 58.70, H 7.74, S 22.39;
found: C 58.52, H 7.62, S 22.41; 1H NMR (400 MHz,
The coated Teflonꢀ tape was washed with CH3CN (4”
1.5 mL) and dried under oil pump vacuum. Another vial
was charged with
a 0.0500M CH3CN solution of 2a
CDCl3): d=6.81–6.78 [m, CH=C
3JH,H =7.0 Hz, CH(CH3)2, 1H], 3.67 [sept, 3JH,H =7.0 Hz,
CH(CH3)2’, 1H], 3.53–3.44 (m, CHCHH’CHH’, 1H), 3.08
[dd, 2JH,H =15.2 Hz, 3JH,H =3.3 Hz, (C=O)CHH’, 1H], 2.48
A
(1.92 mL) and the coated Teflonꢀ tape. The above proce-
dure was repeated. The volume was decreased by 0.080 mL
for each cycle to compensate for the catalyst lost in the ali-
quots. After the final cycle, the Teflonꢀ tape was washed
with CH3CN (4”1.5 mL) and dried under oil pump vacuum,
and the coating dissolved in degassed CF3C6H5. Then 31P
AHCTREUNG
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2
3
[dd, JH,H =15.2 Hz, JH,H =10.2 Hz, (C=O)CHH’, 1H], 2.60–
2.41 (m, CHCHH’CHH’, 2H), 2.25–2.15, 1.84–1.76 (2 m,
CHCHH’CHH’, 2H), 1.32 [d, 3JH,H =7.0 Hz, CH
C
1
3
and H NMR spectra were recorded (data: see text).
6H], 1.29 [d, JH,H =7.0 Hz, CH
A
(101 MHz, CDCl3): d=198.3 [s, (C=O)CH2], 188.8 [s, CH=
(C=O)], 146.7 [s, CH=C(C=O)], 143.1 [s, CH=C(C=O)],
47.8 [s, (C=O)CH2], 42.0 (s, CHCH2CH2), 34.5, 34.3 [2s, CH-
(CH3)2 and CH(CH3)2’], 31.6 (s, CHCH2CH2), 29.1 (s,
CHCH2CH2), 23.15, 22.97, 22.94, 22.91 {4s, CH(CH3)(CH3)’
and [CH(CH3)(CH3)’]’}; IR (thin film): n=1683 (s, nC O),
1652 (s, nC O), 1613 cmÀ1 (s, nC C).
C
A
G
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Recycling Sequence C (Figure 1, C)
This was conducted identically to sequence B, using Gore-
Rastexꢀ fiber (0.160 g) in place of Teflonꢀ tape.
A
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G
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A
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=
Product Characterization
=
=
Cyclized products were purified by silica gel column chro-
matography and characterized as follows.
Syntheses of Educts O=CH
A
G
HOCK H(CH2)2CH=CL
(C=O)Ph (2b)[16b] was obtained (7:3
A
v/v ethyl acetate/pentane) as a pale yellow oil. 1H NMR
(400 MHz, CDCl3): d=7.78–7.75 (m, o-Ph, 2H), 7.59–7.54
(m, p-Ph, 1H), 7.48–7.44 (m, m-Ph, 2H), 6.68 (dd,
CHH’CH=C, 3JH,H =3.0 Hz and 2.8 Hz, 1H), 5.32–5.28 (m,
HOCH, 1H), 3.28 (br s, HO, 1H), 2.80–2.71 (m,
A flask was charged with a solution of a dialdehyde (n=2,
succinaldehyde;[26] 3, glutaraldehyde[27]) in CH2Cl2 (40.0 mL,
0.300M, 12.0 mmol) and cooled to 08C. Then the ylide
Ph3PCH
A
was added dropwise with stirring. The mixture was allowed
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Florian O. Seidel and John A. Gladysz
UPDATES
to warm to room temperature overnight. The solvent was re-
moved and the residue was extracted with ether (3”20 mL).
The ether was removed, and the products were purified by
silica gel column chromatography and characterized as sum-
marized below.
i-PrS
(5a)
A
N
A round-bottom flask was charged with a solution of succi-
naldehyde[26] in CH2Cl2 (17.0 mL, 0.300M, 5.20 mmol). Then
Ph3PCH(C=O)S-i-Pr (4.16 g, 11.0 mmol) dissolved in
E
The known ylides Ph3PCH
U
G
CH2Cl2 (5 mL) was added with stirring. After 1 d, the sol-
vent was removed by rotary evaporation. The residue was
chromatographed (silica gel column, 1:9 v/v ethyl acetate/
pentane) to give 5a as a colorless solid that can be recrystal-
lized from hexanes at À208C; yield: 1.19 g (4.16 mmol,
80%). Anal. calcd. (%) for C14H22O2S2 (286.1): C 58.70, H
7.74, S 22.39; found: C 58.35, H 7.55, S 22.25; 1H NMR
(300 MHz, CDCl3): d=6.81 (dt, 3JH,H =15.4 and 6.10 Hz,
CH2CH=CH, 2H), 6.07 (d, 3JH,H =15.4 Hz, CH2CH=CH,
The new ylide Ph3PCH(C=O)S-i-Pr was synthesized analo-
G
gously to the SEt homolog.[31] Additional details are provid-
ed elsewhere.[32]
O=CHCH2CH2CH=CH
(C=O)Ph (2a)[16b] was obtained
E
(7:3 v/v ethyl acetate/pentane) as a slightly yellow liquid;
yield: 0.643 g (3.42 mmol, 59%). 1H NMR (400 MHz,
3
CDCl3): d=9.79 (s, O=CH, 1H), 7.91 (d, JH,H =7.6 Hz, o-
3
3
Ph, 2H), 7.54 (t, JH,H =7.6 Hz, p-Ph, 1H), 7.44 (dd, JH,H
=
2H), 3.69 [sept, 3JH,H =7.0 Hz, CH
3JH,H =5.6 Hz, CH2CH=CH, 4H), 1.31 [d, JH,H =7.0 Hz, CH-
(CH3)2, 12H]; 13C{1H} NMR (101 MHz, CDCl3): d=189.8 (s,
C=O), 142.3 (s, CH2CH=CH), 129.6 (s, CH2CH=CH), 34.5
[s, CH(CH3)2], 30.3 (s, CH2CH=CH), 23.0 [s, CH(CH3)2]; IR
(powder film): n=1683 (s, nC O), 1652 cmÀ1 (s, nC C).
N
3
7.6 Hz and 7.6 Hz, m-Ph, 2H), 7.00 (dt, JH,H =14.2 Hz and
3
6.3 Hz, CH2CH=CH, 1H), 6.90 (dt, 3JH,H =14.2 Hz, JH,H
=
4
AHCTREUNG
1.3 Hz, CH2CH=CH, 1H), 2.77–2.62 (m, O=CHCH2,
CH2CH=CH, 4H); 13C{1H} NMR (101 MHz, CDCl3): d=
200.4 (s, O=CH), 190.4 [s, (C=O)Ph], 146.6 (s, CH2CH=
CH), 137.6 (s, i-Ph), 132.8 (s, p-Ph), 128.54, 128.51 (2s, o-,
m-Ph), 126.7 (s, CH2CH=CH), 41.9 (s, O=CHCH2), 24.9 (s,
G
ACHTREUNG
=
=
CH2CH=CH); IR (thin film): n=1721 (s, nC O), 1669 (s,
=
nC O), 1619 cmÀ1 (s, nC C).
O=CHCH2CH2CH=CH(C=O)S-i-Pr (3a) was obtained
=
=
Acknowledgements
A
(1:4 v/v ethyl acetate/pentane) as a colorless oil; yield:
0.766 g (4.11 mmol, 71%). Anal. calcd. (%) for C9H14O2S
(186.1): C 58.03, H 7.58, S 17.21; found: C 57.82, H 7.78, S
16.80; 1H NMR (400 MHz, CDCl3): d=9.78 (s, O=CH,
We thank the Deutsche Forschungsgemeinschaft [DFG, GL
300/3–3 and GL 300/8–1 (SPP 1179)] and the Welch Founda-
tion for support.
3
1H), 6.82 (dt, JH,H =15.5 Hz and 6.8 Hz, CH2CH=CH, 1H),
6.08 (d, 3JH,H =15.5 Hz, CH2CH=CH, 1H), 3.70 (sept, 3J-
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G
U
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1
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asc.wiley-vch.de
2449