Preparation of Propargylic Sulfinates and their [2,3]-Sigmatropic Rearrangement to Allenic Sulfones

Article abstract of DOI:10.1002/adsc.201600986

The scope of the [2,3]-sigmatropic rearrangement of propargylic sulfinates to allenic sulfones by silver catalysis was expanded. A series of new propargylic sulfinate esters was generated from a variety of aromatic and heteroaromatic sulfonyl chlorides an

Full text of DOI:10.1002/adsc.201600986

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DOI: 10.1002/adsc.201600986
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Preparation of Propargylic Sulfinates and their [2,3]-Sigmatropic
Rearrangement to Allenic Sulfones
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Rama Rao Tata,a Carissa S. Hampton,a and Michael Harmataa,*
a
Department of Chemistry, University of Missouri-Columbia, Columbia Missouri 65211, (USA)
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Fax: (+1)-573-882-2754; e-mail: harmatam@missouri.edu
Received: September 6, 2016; Revised: December 15, 2016; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201600986
Abstract: The scope of the [2,3]-sigmatropic rear-
rangement of propargylic sulfinates to allenic
sulfones by silver catalysis was expanded. A series
of new propargylic sulfinate esters was generated
from a variety of aromatic and heteroaromatic
sulfonyl chlorides and their rearrangement to
allenic sulfones is reported. In addition, the syn-
Scheme 1. Stirlingꢀs synthesis of allenic sulfones.
thesis of propargylic sulfinate esters containing
electron-withdrawing benzenesulfonyl chlorides is
At nearly the same time, Braverman and cow-
reported.
orkers reported the rearrangements of propargylic
sulfinates to sulfones (or sulfenates to sulfoxides),
Keywords: allene; sigmatropic rearrangement; sil-
ver; sulfone
which they suggested occurred by a cyclic intra-
molecular mechanism (Scheme 3A).[8] This intramo-
lecular rearrangement was proposed based on analo-
gous observations of propargylic phosphites and
phosphinites reported by Boiselle and Meinhardt in
1962 (Scheme 2).[9] Thus, the lone pair of electrons on
Introduction
the phosphorus/sulfur atom attacks the ethynyl car-
36 Allenic sulfones are structurally interesting and pos- bon, simultaneously cleaving a CÀO bond to give the
37 sess an interesting chemistry.[1] They have been allenic phosphorus oxide/sulfone via a [2,3]-sigma-
38 applied in many types of reactions including cycliza- tropic rearrangement (Schemes 2 and 3).[8]
39 tions,[2] cycloadditions,[3] and Claisen rearrangements,[4]
40 among others. Two advantages of using the sulfone
41 group to activate an allene are that it serves as an
42 electron-withdrawing group that enhances reactivity
43 and can also be easily removed by various desulfony-
44 lation methods, thereby serving as an traceless direct-
45 ing group.[5]
46
The first report of an allenic sulfone was in 1964 by
47 Stirling, who studied the interconversions of phenyl-
48 sulfonylpropadiene, 1-phenylsulfonylpropyne, and 3-
49 phenylsulfonylpropyne (Scheme 1A).[6] The latter
50 could be easily isomerized into the thermodynamically
51 more stable allenic sulfone in the presence of triethyl-
52 amine. In 1967, Stirling reported the conversion of 2-
53 propynyl p-toluenesulfinate to the propadienyl p-
54 tolylsulfone by heating at reflux in chlorobenzene
Scheme 2. Synthesis of phosphorylated allenes via a [2,3]-
sigmatropic rearrangement.
The rearrangement of propargylic sulfinate esters
55 (Scheme 1B).[7] The mechanism for this transforma- into allenic sulfones is a concerted process that is
56 tion was not known at the time.
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intramolecular and irreversible. This has been demon-
strated by several studies examining kinetics,[8a,10]
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salts and a copper-doped zeolite, Cu1-USY (Sche-
me 3F).[16] Copper salts with the non-coordinating
anions performed better. However, the copper-cata-
lyzed [2,3]-sigmatropic rearrangement was signifi-
cantly slower than the silver-catalyzed process.
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Recently, we reported a few new reactions of
allenic sulfones. We introduced a regiodivergent
isomerization to either a 1-arylsulfonyl-1,3-diene 12
via palladium catalysis or a 2-arylsulfonyl-1,3-diene 13
via nucleophilic catalysis (Scheme 4).[17] The second
application involved the formation of the hydroxyal-
lene 14, which can then undergo a series of sigma-
tropic rearrangements to generate hydroxyenones
15.[18] This then further cyclizes under acidic conditions
to form furanones 16 (Scheme 4).[19]
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Scheme 3. [2,3]-Sigmatropic rearrangement of a propargylic
sulfinate.
16 deuterium labeling,[11] and stereochemical outcomes.[11]
17 Braverman and coworkers published a review of [2,3]-
18 sigmatropic rearrangements of propargylic and allenic
19 sulfur derivatives in 2007.[12]
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Since the initial studies of this rearrangement,
21 others have shown that this [2,3]-sigmatropic rear-
22 rangement can be realized under mild reaction
23 conditions. Many of these methods employ the use of
24 transition metal catalysts such as palladium,[13] rhodi-
25 um,[14] silver,[15] copper,[16] and metal-doped zeoli-
26 tes.[15b,16]
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In 2005, Mukai and coworkers reported the syn-
28 thesis of allenic sulfones via a rhodium-catalyzed [2,3]-
29 sigmatropic rearrangement.[14] The sulfinate esters
30 were charged with a catalytic amount of di-m-chlorote-
31 tracarbonyldirhodium(I) at room temperature and
32 afforded the allenic sulfones in only 30 min (Sche-
33 me 3B).
Scheme 4. Recent applications of allenic sulfones from the
Harmata group.
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Hiroi and coworkers reported the synthesis of
Our interest in multiple areas employing allenic
35 chiral allenic sulfones in 1998 and 2001.[13a,b] The sulfones as precursors led us to further examine their
36 treatment of 3-methylpropargyl sulfinate (87% ee) preparation. The scope of sulfinate ester preparation
37 with 5 mol% palladium acetate and 7.5 mol% of 1,2- and transformation to allenic sulfones has been greatly
38 bis(diphenylphosphino)ethane (dppe) resulted in the expanded by the work herein.
39 corresponding allenic sulfone (85% ee) in moderate
40 yield over 18 h (Scheme 3C).
It should be noted that there have been multiple
methods for synthesizing sulfinate esters. One of the
41
In 2008, we reported the rapid conversion of first was in 1965 when Douglass described a method in
42 propargylic sulfinates to allenic sulfones by silver which a disulfide was reacted with acetic acid and
43 catalysis (Scheme 3D).[15a,c] The treatment of propar- chlorine gas to prepare a sulfinyl chloride (Eq. 1).[20]
44 gylic sulfinate esters with 2 mol% of silver hexafluor- This crude material was then reacted with an alcohol
45 oantimonate (AgSbF6) afforded the corresponding to generate the desired sulfinyl ester. This method is
46 allenic sulfones in excellent yields in just 2 minutes. hampered by the thermal instability and moisture-
47 The advantage of using silver salts over other methods sensitivity of sulfinyl chlorides. In addition, sulfinyl
48 include a shorter reaction time, a lower catalyst chlorides tend to disproportionate into sulfonyl and
49 loading, no tedious workup or purification, and nearly sulfenyl chlorides.[21] Douglass later reported that the
50 quantitative yields.
sulfinate esters could be made directly by low-temper-
51
We recently reported that silver salts containing ature chlorination of disulfides in alcohols (Eq. 2).
52 the most non-coordinating counterions were the This is also complicated by the formation of sulfinyl
53 fastest and most effective catalysts in this rearrange- and sulfonyl chlorides as well as the corresponding
54 ment (Scheme 3E).[15b] In addition, a silver-doped thiolsulfonic ester, RSO2SR.[22]
55 zeolite, Ag1-USY, could be used as a recoverable,
(Eq. 1)
56 recyclable green catalyst alternative. Hampton and
57 Harmata also reported a similar study using copper
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propargyl alcohol and Ph3P in CH2Cl2 dropwise to a
chilled solution (08C) of p-toluenesulfonyl chloride
and triethylamine in CH2Cl2. The reaction was then
stirred at room temperature until complete conversion
(Eq. 2)
In 1987, Sharpless and Klunder described a one- of the sulfonyl chloride was observed by TLC analysis.
step synthesis of sulfinate esters via an in situ reduc- The results are shown in Table 1. Tertiary propargyl
tion of readily available sulfonyl chlorides (Eq. 3).[23] alcohols 19 and 21–22 (Table 1, entries 1 and 3–4)
One significant problem with this technique though generally produced the esters in higher yields than
was the formation of a phosphorothiolate byproduct secondary propargyl alcohols 20 and 24–28 (Table 1,
10 of the form ArSP(O)(OR)2.[24] In 1999, Toru and entries 2, 5–9). When attempting to prepare the
11 coworkers reported an improved procedure by em- sulfinate ester derived from 2-phenylbut-3-yn-2-ol 23,
12 ploying triphenylphosphine as the reducing agent the allenic sulfone 33 was isolated directly with no
13 instead of trimethylphosphite.[25] This method worked trace of the ester (Table 1, entry 4) due to spontaneous
14 well for chiral alcohols to prepare chiral sulfinate rearrangement, similar to certain observations made
15 esters.
by Braverman.[26]
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After examining the propargylic alcohols for ester
preparation with a simple sulfonyl chloride, we studied
several other aromatic and heteroaromatic sulfonyl
(Eq. 3)
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Hajipour and coworkers have reported two sepa- chlorides using the tertiary alcohol 19 as a substrate.
20 rate methods for preparing sulfinate esters in a The sulfinate esters were prepared as above; the
21 solvent-free fashion. In 1999, they demonstrated that a results are summarized in Table 2. The yields were fair
22 mixture of a sulfonyl chloride, menthol, trimethyl- to good and in some cases byproducts of mixed
23 phosphite, and silica gel could be ground with a pestle anhydrides or disulfides were formed. Some of these
24 in a mortar to prepare the corresponding sulfinate byproducts were identified and characterized, but
25 ester in 20 minutes or less in yields of 70–88% (Eq. were not pursued further.
26 4).[26] Later in 2006, they described another method in
In this study, the p-toluene derivative was synthe-
27 which an alcohol, a sulfinic acid, and dicyclohexylcar- sized in 71% yield, which corresponds well with our
28 bodiimide (DCC) could be ground in a mortar and previously reported yield.[15c] When benzenesulfonyl
29 pestle in 15 min to yield the sulfinate esters in 80–98% chloride and 2-naphthalenesulfonyl chloride were
30 yields (Eq. 5).[27]
treated under the same conditions the resultant
sulfinate esters 41 and 42 were isolated in 74% and
68% yield, respectively (Table 2, entries 2–3). To
examine the effect of sterics on this reaction, mesityl-
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(Eq. 4)
(Eq. 5)
sulfonyl chloride
chloride) and
(2,4,6-trimethylbenzenesulfonyl
2,4,6-tri-iso-propylbenzenesulfonyl
chloride were reacted with 19 and both resulted in the
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In 2008, our group reported the synthesis of corresponding sulfinate esters 43 and 44 in moderate
38 sulfinate esters using Toru’s method in our study of 50% and 48% yields, along with the related disulfide
39 their [2,3]-sigmatropic rearrangement to allenic sul- byproducts in 17% and 18% yield, respectively
40 fones (Eq. 6).[15c]
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(Table 2, entries 4–5). The disulfides are a result of
overreduction of the sulfonyl chlorides to sulfenyl
chlorides by triphenylphosphine. The results suggest
that the formation of side products depends on the
(Eq. 6)
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This discussion has not been exhaustive; other steric nature of the sulfonyl chlorides and the reducing
45 methods for sulfinate ester formation can be found in capacity of the phosphorus agent. There seems to be a
46 the literature.[28]
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significant electronic effect of the formation of
sulfinate esters. The p-methoxybenzenesulfonyl
chloride was used to prepare sulfinate 45 easily in
73% yield, but when attempting to prepare esters
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Results and Discussion
50 We initially describe the synthesis of new propargylic from sulfonyl chlorides that possess electron-with-
51 sulfinate esters by methods similar to some of those drawing aromatic groups, the yields are much lower.
52 that have been reported previously, followed by a new The p-bromobenzene and pentafluorobenzene deriva-
53 approach using sulfonyl chlorides containing electron- tives 46 and 47 were isolated in 54% and 44% yields,
54 withdrawing groups.
respectively (Table 2, entries 7–8). The p-trifluorome-
55
We began by varying the substitution on the thylbenzene, 3,5-bis(trifluoromethyl)benzene (BTFB),
56 propargylic alcohol starting material. A collection of and p-nitrobenzene derivatives yielded the esters 48–
57 sulfinate esters was prepared by adding a solution of a 50 in very poor yields of 28%, 27%, and 33%,
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Table 1. Varying alkyl substitution of propargylic sulfinate
esters.
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Scheme 5. Variation in allene substitution of tosylated allenic
sulfones.
instead.[26] Trimethylphosphite could also be used to
prepare 52 in 68% yield as well (Table 2, entry 13).
2-Pyridinesulfonyl chloride produced the sulfinate
ester 53 in a moderate yield of 51% and the N-methyl-
3-carbazolesulfonyl chloride generated 54 in 38%
yield (Table 2, entries 13–14) when using PPh3 as the
reducing agent. A single example employing an
aliphatic sulfonyl chloride allowed the formation of
ester 55 in 16% yield. This result is somewhat
expected as Klunder and Sharpless reported that
sulfinate ester formation is not suitable for sulfonyl
chlorides possessing a-hydrogens because deprotona-
tion to form a sulfene intermediate is favored and this
prevents reduction of the sulfonyl chloride by the
phosphine.[23]
(a) The allenic sulfone 33 was isolated directly in 73% yield.
After their preparation, all of the propargylic
sulfinate esters were treated with silver hexafluoroan-
timonate in dichloromethane at room temperature to
induce a [2,3]-sigmatropic rearrangement to afford the
corresponding allenic sulfones (Scheme 5-6). All reac-
tion times were short, generally within 30 minutes,
(b) Isolated as a 1.4:1.0 mixture of 34 (52%):sulfonate ester
(35%).
(c) Cy=cyclohexyl.
48 respectively (Table 2, entries 9–11). To examine the with the majority within 10 minutes, and produced
49 suitability of heterocyclic sulfonyl chlorides in the excellent yields of the rearranged products. Isolation
50 process, sulfinate esters were prepared from 2-thio- of the allenes was facile; simply filtering the reaction
51 phenesulfonyl chloride, 2-pyridinesulfonyl chloride, solution through a Celiteꢂ pad in a sintered funnel
52 and N-methyl-3-carbazolesulfonyl chloride. The 2- followed by evaporation of the solvent yields the pure
53 thiophenesulfonyl chloride generated the sulfinate product. In the case of the TMS allene 58, the crude
54 ester 51 in only 40% yield under triphenylphosphine NMR was ~95% pure and when purification by
55 conditions (Table 2, entry 12), but the yield could be column chromatography was attempted the product
56 increased to 55% if trimethylphosphite was used decomposed. It is important to mention that the
57
pyridine-substituted and N-methyl-3-carbazole-substi-
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Table 2. Variation of the sulfinate group of propargylic sulfinate esters.
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(a) 2-Naph=2-naphthyl.
(b) Mesityl=2,4,6-trimethylphenyl.
(c) Trisyl=2,4,6-tri-iso-propylphenyl.
(d) Disulfide was isolated in 17% yield.
(e) Disulfide was isolated in 18% yield.
(f) Trimethylphosphite was used instead of triphenylphosphine.
(g) 1-ethynylcyclohexanol was used instead of 19.
55 tuted esters did not undergo the [2,3]-sigmatropic resulted in decomposition of the starting materials.
56 rearrangement; only starting material was recovered The nitrogen in these compounds may have coordi-
57 in each case. Stoichiometric AgSbF6 was also used, but nated to the silver ion and prevented its coordination
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Table 3. Optimization of 3,5-bis(trifluoromethyl)benzene
sulfinate esters.(a)
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7
8
9
Entry Phosphorus Re-
agent
Base
T
8C
Time Yield
49
(%)
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15
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17
18
19
20
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40
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2
3
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6
PPh3
NEt3
NEt3
NEt3
pyridine
0
0
30 m 27
30 m 30
P(o-Tol)3
P(OMe)3
P(OMe)3
P(OMe)3
P(OMe)3
À20 1 h 43
À20 1 h 40
Imidazole À20 1 h 40
2,6-luti-
dine
À20 1 h 42
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8
9
10
11
12
P(OiPr)3
P(OEt)3
P(OPh)3
PPh2Cl
P(OH)(OEt)2
P(OH)(OEt)2
NEt3
NEt3
NEt3
NEt3
NEt3
NEt3
0
0
0
0
0
1 h 40
1 h 38
1 h 33
1 h 22
20 m 67
40 5 m 87
(a) Reactions were run with 1.1 equivalents of base and 1.1
equivalents of the phosphorus reagent in dichloromethane
at 0.1 M.
Scheme 7. Modified conditions for electron-withdrawing
sulfonyl chlorides.
Scheme 6. Variation in sulfone substitution of allenic sul-
fones.
However, the reaction conditions described to this
point were not effective in producing high yields of
41 to the triple bond, thus precluding the [2,3]-sigma- the desired sulfinate esters when electron-poor
42 tropic rearrangement process under the reaction sulfonyl chlorides were used (see Table 2).
43 conditions.
We thus set out to optimize the preparation of
44
Our group has had a longstanding interest in the certain sulfinate esters, specifically 3,5-bis(trifluoro-
45 (4+3)-cycloaddition reaction.[30] In some methods, we methyl)benzene (BTFB) sulfinate esters, through
46 have utilized allenic sulfones to generate alkoxyallylic varying the trivalent phosphorus source using alcohol
47 sulfones[3a] or (trimethylsilyl)methyl allylic sulfo- 19 as the substrate. When the alcohol and the
48 nes,[3d,28] which can used as allylic cations precursors BTFBsulfonyl chloride were treated with triphenyl-
49 for the (4+3)-cycloaddition reactions. We have won- phosphine and TEA as described previously, the ester
50 dered whether a sulfone group better at leaving than a was obtained in only 27% yield. The disulfide by-
51 phenylsulfonyl would have a significant effect on the product 80 was formed in 17% yield (Table 3, entry 1).
52 (4+3)-cycloaddition reaction. For example, we are The use of trimethylphosphite[23] in CH2Cl2 with bases
53 interested in learning if something like a 3,5-bis such as triethylamine, pyridine, imidazole, and 2,6-
54 (trifluoromethyl)benzenesulfonyl group, would be lutidine, only resulted in yields near 40% within 1
55 more effective in certain (4+3)-cycloaddition proto- hour at À208C (Table 3, entries 3–6). We examined
56 cols we have developed.
different phosphorus (III) compounds including tri-
57
ortho-tolylphosphite, triethylphosphite, tri-iso-propyl-
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Table 4. Synthesis of 3,5-bis(trifluoromethyl)benzene sulfi-
nate esters.
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Scheme 8. Variation in allene substitution of BTFB allenic
sulfones.
when the reaction was performed at 408C in dichloro-
methane (Table 3, entry 12).
After developing a high yielding synthesis of 49,
the scope was examined with a variety of propargyl
alcohols. Treatment of 3,5-bis(trifluoromethyl)benze-
nesulfonyl chloride in CH2Cl2 with propargyl alcohols
19 and 22 followed by triethylamine and then dieth-
ylphosphite and heating to reflux for 5–10 minutes
produced the corresponding sulfinate esters 49 and 88
in 87% and 83% yields, respectively (Table 4, en-
tries 1–2). When propargyl alcohol 23 was subjected to
the reaction conditions, the sulfinate ester was not
isolated, instead the corresponding allenic sulfone 89
was isolated directly (Table 4, entry 3), similar to the
tosyl derivative in Table 1, entry 4. Cyclic tertiary
chlorodiphenyl propargylic alcohols also produced sulfinate esters 90–
(a) Product was isolated as a mixture of diastereomers 88 and
allenic sulfone 99 in a 1.0:0.8:0.3 ratio.
(b) The allenic sulfone 89 was isolated directly in 91% yield.
(c) Isolated as a 1.0:0.7 mixture of 93:103.
47 (d) Isolated as a 1.0:0.4 mixture of 94:104.
48
49
50 phosphite,
triphenylphosphite,
51 phosphine, and diethylphosphite (Table 3, entries 2, 93 in good yields (Table 4, entries 4–7). As before,
52 and 7–11). These all resulted in yields of 49 at 40% primary and secondary propargylic alcohols 85–87
53 and below at 08C in dichloromethane, with the were also used to prepare esters 94–96 in moderate
54 exception of diethylphosphite, which gave the sulfi- yields (Table 4, entries 8–10).
55 nate ester in 67% yield at 08C within 20 minutes
After optimization of the synthesis of BTFB
56 (Table 3, entry 11). The yield increased to 87% yield sulfinate esters, these conditions were also applied to
57
the other electron-poor sulfonyl chlorides. The p-
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trifluoromethylbenzene sulfinate ester 48 and the p- Procedure 2: Preparation of Propargylic Sulfinate
nitrobenzene sulfinate ester 50 were prepared in 74% Esters Using Diethyl Phosphite
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4
5
6
7
8
and 57% yields, respectively, using this approach
(Scheme 7).
2-Methylbut-3-yn-2-yl 3,5-bis(trifluoromethyl)benzenesulfi-
nate (49): 3,5-Bis(trifluoromethyl)benzene sulfonyl chloride
(1.0 g, 3.19 mmol, 1.0 equiv.) was added to an oven-dried
100 mL round bottom flask in a glove chamber filled with
argon. To the reaction flask was added 16 mL dichloro-
methane, 2-methyl-3-butyn-2-ol (0.619 mL, 6.39 mmol,
All of the propargylic sulfinate esters bearing
electron-poor sulfur substituents were then subjected
to silver hexafluoroantimonate to induce a [2,3]-
sigmatropic rearrangement to afford the correspond-
9
ing allenic sulfones (Scheme 8). All reaction times 2.0 equiv.), triethylamine (0.891 mL, 6.39 mmol, 2.0 equiv.)
and diethyl phosphite (0.824 mL, 6.38 mmol, 2.0 equiv.)
dropwise sequentially via syringe. The reaction was stirred at
408C for 5–10 min. After completion of reaction by TLC, the
reaction mixture was quenched with water and extracted
with dichloromethane. The combined organic layers were
washed with 1 N HCl, saturated NaHCO3, and brine. The
organic layer was then dried over anhydrous Na2SO4,
filtered, and concentrated in vacuo. The crude product was
purified by flash column chromatography (3% EtOAc:Hex-
10 were short and produced excellent yields of the
11 rearranged products, which were isolated via simple
12 filtration through Celiteꢂ to remove the catalyst and
13 isolate the pure product.
14
Unfortunately, applying these reaction conditions
15 to the synthesis of 53 and 55 resulted in yields of 18%
16 and 15%, respectively. Attempted formation of 54
17 resulted in no reaction.
1
18
anes) to yield 49 as a colorless oil in 87% yield (0.96 g). H
19
20
NMR (500 MHz, CDCl3) d 8.18 (s, 2H), 8.04 (s, 1H), 2.90 (s,
1H), 1.85 (s, 3H), 1.72 (s, 3H); 13C NMR (125 MHz, CDCl3) d
149.2, 132.7 (q, J=33.8 Hz), 125.6 (m), 122.7 (q, J=
271.3 Hz), 77.0, 76.7, 30.8, 30.5; IR (cmÀ1) 3309, 3264, 3077,
2991, 2933, 2116, 1622, 1360, 1274, 1180, 1135, 1099, 899, 772;
HRMS m/z calcd for (C13H10F6O2S)Na+ 367.0198, found
367.0195.
Conclusions
21 In summary, we have expanded the scope of the
22 preparation of various propargylic sulfinate esters
23 from a variety of arylsulfonyl chlorides. We have also
24 optimized the synthesis of the more electron-with-
25 drawing 3,5-bis(trifluoromethyl)benzene sulfinate es-
26 ters. In addition, most of the sulfinate esters prepared
27 underwent a [2,3]-sigmatropic rearrangement to yield
28 the corresponding allenic sulfones very rapidly and in
29 excellent yields. The allenic sulfones prepared herein
30 may be used in several types of reaction that have
31 been recently reported and additional reactions whose
32 results will be reported in due course.[32]
Procedure 3: Preparation of Propargylic Sulfinate
Esters Using Trimethylphosphite
2-Methylbut-3-yn-2-yl thiophene-2-sulfinate (51): The sulfi-
nate ester was prepared according to literature method. In a
flame-dried round bottom flask under argon atmosphere, 2-
thiophene sulfonyl chloride (535 mg, 2.93 mmol, 1.5 eq) was
dissolved in CH2Cl2 (25 mL) and 2-methyl-3-butyn-2-ol
(164 mg, 1.95 mmol, 1.0 eq) was added to the flask. A
solution of triethylamine (0.41 mL, 2.93 mmol, 1.5 eq) and
trimethylphosphite (0.46 mL, 3.90 mmol, 2.0 eq) in CH2Cl2
(5 mL) was added dropwise to the reaction solution. The
reaction was stirred and stirred at reflux for 3 h. The reaction
was cooled and poured into a mixture of diethyl ether:1 N
HCl (2:1, 30 mL). The ethereal layer was washed with
saturated NaHCO3 and brine. The organic layer was then
dried over anhydrous sodium Na2SO4, filtered, and concen-
trated in vacuo. The crude product was purified by column
chromatography (3% EtOAc:Hex) to yield 51 as a white
solid (mp=62-638C) in 55% yield (0.230 g). 1H NMR
(500 MHz, CDCl3) d 7.62 (dd, J=5.0 Hz, J=1.0 Hz, 1H),
7.49 (dd, J=4.0 Hz, J=1.0 Hz, 1H), 7.13 (dd, J=5.0 Hz, J=
4.0 Hz, 1H), 2.78 (s, 1H), 1.81 (s, 3H), 1.71 (s, 3H); 13C NMR
(125 MHz, CDCl3) d 149.0, 131.3, 129.4, 127.5, 84.0, 75.9,
75.7, 30.9, 30.6; IR nmax (cmÀ1) 3225, 3098, 3082, 3070, 2983,
2927, 2109, 1227, 1187, 1136, 1108, 1012, 949, 846, 762, 742,
691; HRMS m/z calcd for (C9H10O2S2)Na+ 237.0014, found
237.0013.
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Experimental Section
36 Procedure 1. Preparation of Propargylic Sulfinate
37 Esters Using Triphenylphosphine
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1-Methyl-4-((3-methylbuta-1,2-dien-1-yl)sulfonyl)benzene
(29): In a flame-dried round bottom flask under argon
atmosphere, the p-toluenesulfonyl chloride (4.53 g,
23.77 mmol, 1.0 eq) was dissolved in CH2Cl2 (80 mL) and
triethylamine (3.31 mL, 26.15 mmol, 1.1 eq) was added. A
solution of 2-methyl-3-butyn-2-ol (2.00 g, 23.77 mmol, 1.0 eq)
44 and triphenylphosphine (6.24 g, 23.77 mmol, 1.0 eq) in CH2
Cl2 (20 mL) was added dropwise to the reaction solution at
08C over 1 hour. The reaction was stirred at room temper-
ature and monitored by TLC until consumption of sulfonyl
chloride. The reaction was quenched with water and
extracted with CH2Cl2. The organic extracts were concen-
trated on the rotary evaporator. The crude product was
purified by column chromatography (3% EtOAc: Hex) to
yield 29 as a white solid in 71% yield (3.75 g). 1H NMR
(500 MHz, CDCl3) d 7.62 (d, J=8.0 Hz, 2H), 7.32 (d, J=
8.0 Hz, 2H), 2.78 (s, 1H), 2.42 (s, 3H), 1.81 (s, 3H), 1.68 (s,
1H); 13C NMR (125 MHz, CDCl3) d 143.3, 142.4, 129.6,
124.9, 84.7, 75.4, 75.3, 30.9, 30.6, 21.5. The spectral data
matched that previously reported in the literature.
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Procedure 4: [2,3]-Sigmatropic Rearrangement Using
Silver Hexafluoroantimonate
To a solution of the sulfinate ester in CH2Cl2 (0.1 M) under
an argon atmosphere was added silver hexafluoroantimonate
(2 mol%). The reaction was stirred at room temperature and
monitored by TLC until complete conversion of starting
material. The reaction mixture was filtered through Celite in
a sintered glass funnel, rinsing with more CH2Cl2, and the
filtrate was concentrated in vacuo to yield the pure allenic
sulfone.
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Acknowledgements
This work was supported by the National Science Foundation
and the Department of Chemistry at the University of
Missouri-Columbia to whom we are grateful. We thank Dr.
Charles L. Barnes (Missouri-Columbia) for acquisition of the
X-ray data.
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chloride) contain the supplementary crystallographic
data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
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[32] CCDC-1502426 (80) and CCDC-1502427 (disulfide
derived
from
2,4,6-tri-iso-propylbenzenesulfonyl
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