[2,3] sigmatropic rearrangement of propargylic sulfinates by a pale Ag1-USY zeolite and silver salts

Article abstract of DOI:10.1002/adsc.201400978

The sigmatropic rearrangement of propargylic sulfinates to allenic sulfones is catalyzed by the silver cation. The Ag¹-USY zeolite, as well as non-coordinating silver salts, lead to essentially quantitative yields of the corresponding allenic s

Full text of DOI:10.1002/adsc.201400978

UPDATES
DOI: 10.1002/adsc.201400978
[2,3]Sigmatropic Rearrangement of Propargylic Sulfinates by
a Pale Ag1-USY Zeolite and Silver Salts
Carissa S. Hamptona and Michael Harmataa,*
a
Department of Chemistry, University of Missouri–Columbia, Columbia, Missouri 65211, USA
Fax : (+1)-573-882-2754; e-mail: harmatam@missouri.edu
Received: November 11, 2014; Revised: December 4, 2014; Published online: && &&, 0000
Dedicated to the memory of Carl E. Hampton (August 22, 1931 – December 14, 2013)
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201400978.
Abstract: The sigmatropic rearrangement of propar-
gylic sulfinates to allenic sulfones is catalyzed by
the silver cation. The Ag1-USY zeolite, as well as
non-coordinating silver salts, lead to essentially
quantitative yields of the corresponding allenic sul-
fones.
Given our interest in allenic sulfones,[8] the current
interest in silver-catalyzed reactions,[9] and the grow-
ing interest in green chemistry,[10] we wondered
whether there was another way to catalyze the rear-
rangement. An emerging area of synthetic chemistry
utilizing metal-doped zeolite catalysts[11] led us to de-
termine whether a zeolitic catalyst could be of use in
our allenic sulfone preparation.
Many zeolites are easily recoverable and reusable
and therefore pose an advantage over some other cat-
alyst systems. Zeolites have a storied history of use in
industry,[12] but more recently work has been per-
formed using metal-doped zeolites to catalyze organic
Keywords: allenes; sigmatropic rearrangement;
silver; sulfones; zeolites
The [2,3]sigmatropic rearrangement of propargylic transformations. Copper-doped zeolites are gaining
sulfinate esters to allenic sulfones was first demon- recognition in the area of cycloadditions and homo-
strated in the mid 1960s, concurrently by Stirling and coupling,[11a,d,e,13] but there are very few examples of
by Braverman and Mechoulam.[1] The rearrangement silver zeolite-catalyzed reactions.[11c,14]
was suggested to occur via a cyclic intramolecular
Given the facility of the [2,3]sigmatropic rearrange-
mechanism. Later kinetic studies,[1a,2] deuterium label- ment in the presence of catalytic silver hexafluoroan-
ing studies,[3] and stereochemical studies[3] definitively timonate,[7b] the notion of silver-doped zeolite cata-
categorized this rearrangement as a concerted, cyclic, lysts was an ideal route to pursue. The zeolite used in
intramolecular, and irreversible process rather than this study is the Ag1-USY introduced by Pale, whose
one occurring by dissociation/recombination. An anal- framework consists of spherical cage-like pores with
ogous transformation is also seen in the [2,3]sigma- average diameter of 7.4 ꢀ wherein the rearrangement
tropic rearrangement of trivalent propargylic or allylic may occur.[13e,14,15]
phosphorus compounds.[4] Typical rearrangements of
Initially, we began with an examination of several
propargylic sulfinates to allenic sulfones can be ac- solvents to determine the most efficient medium for
complished by thermolysis.[1] The conversion has also the reaction. We believed that dichloromethane or ni-
been catalyzed by rhodium,[5] palladium,[6] and recent- troethane would be the best choice as per previous
ly, silver.[7]
work[7b] and this turned out to be correct. 1,2-Di-
In 2008, we reported the silver-catalyzed rearrange- chloroethane also worked well. The reaction required
ment of propargylic sulfinates to allenic sulfones by much longer reaction times in other solvents, but re-
silver hexafluoroantimonate [Eq. (1)].[7b] This was sulted in similarly excellent yields, with the exception
a straightforward and mild process giving excellent of diethyl ether and trifluorotoluene, in which the re-
yields of the corresponding allenic sulfones.
action did not go to completion. In most cases, the
majority of the zeolite catalyst was recovered by fil-
tration through a nylon membrane. The results are
summarized in Table 1.
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Carissa S. Hampton and Michael Harmata
Table 1. Solvent effects on the Ag1-USY-catalyzed rear-
Table 3. Successive reuse of Ag1-USY zeolite.
rangement.
Entry[a] Catalyst Time
[h]
Catalyst Recovered
[%][a}
Yield
[%]
Entry Solvent
Time Catalyst Recovered Yield
[h]
[%][a]
[%]
1
2
3
Run 1
Run 2
Run 3
4.5
5
6
76
78
74
99
100
93
1
2
CH2Cl2
THF
4.5
78
32
–
60
–
81
–
97
73
97
[b]
3
4
toluene
Et2O
[a]
[c]
The recovered catalyst was scraped from the nylon mem-
brane before weighing, rather than determining the dif-
ference of the membrane with and without recovered
catalyst. Therefore, observed recovery is lower than
actual recovery due to adherence of particles to the
membrane.
–
5
6
7
ClCH2CH2Cl 7.5
MeCN 66
1,4-dioxane 36
77
–
97
94
–
100
100
100
100
[b]
8
9
10
EtNO2
PhCF3
EtOAc
8
–
[c]
–
24
60
100
[a]
The recovered catalyst was scraped from the nylon mem-
brane before weighing, rather than determining the dif-
ference of the membrane with and without recovered
catalyst. Therefore, observed recovery is lower than
actual recovery due to adherence of particles to the
membrane.
Table 4. Ag1-USY zeolite rearrangements of propargylic sul-
finates.
[b]
[c]
Catalyst not able to be recovered.
The reaction did not go to completion even after 1 week.
Entry Ar
R1/R2
Time Catalyst
[h]
Yield
Recovered [%][a] [%]
1
2
3
4
Ph
Me/Me
4
94
42
96
59
98
96
99
99
Table 2. Effects of Ag1-USY zeolite catalyst loading.
2-naphthyl Me/Me 32
Tris[b]
Me/Me 30
-(CH2)5- 3 d
p-Tol
[a]
The recovered catalyst was scraped from the nylon mem-
brane before weighing, rather than determining the dif-
ference of the membrane with and without recovered
catalyst. Therefore, observed recovery is lower than
actual recovery due to adherence of particles to the
membrane.
Entry[a] Catalyst Loading Time Catalyst Recov- Yield
[mol%]
[h]
ered [%][a]
[%]
1
2
3
4
3.5
4.5
7.0
10.0
5.5
4.5
4
100
94
100
100
100
99
100
95
[b]
Tris=2,4,6-triisopropylbenzene.
3
[a]
Recovered catalyst determined by difference of nylon
membrane mass with and without zeolite recovered.
decrease in yield, but that reaction times increased
with each successive reuse (Table 3).
After determining that dichloromethane was a suita-
The catalyst was removed by filtration over a nylon
ble solvent, we examined the effect of catalyst load- membrane and air-dried by aspiration. Weighing the
ing.[16] When the sulfinate was treated with a loading dried catalyst on the membrane indicated nearly
of 3.5 mol% of silver cation, the rearrangement was quantitative recovery, but when scraped from the
concluded in 5.5 h. As the catalyst loading was in- nylon membrane, collected in a vial, and weighed,
creased upwards to 15 mol%, no significant improve- a less than quantitative recovery was observed due to
ment on the reaction was observed other than slightly some particles that remain adsorbed in or on the
shorter reaction times (Table 2).
membrane.
Previously, silver zeolite catalysts have been activat-
We also tested the ability of the Ag1-USY to cata-
ed prior to use and after recovery by heating at very lyze the rearrangement of a few other propargylic sul-
high temperatures to prevent silver reduction.[11c,14] finates. The results can be seen in Table 4. The reac-
We found that the zeolites can also be used directly tion of the simple phenyl system was similar to the
without preactivation between runs. We examined the aforementioned para-toluene system with respect to
recyclability of the zeolites and found that they can both time and yield. The other more hindered sulfi-
be used at least three times without any significant nates required longer reaction times for complete
2
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[2,3]Sigmatropic Rearrangement of Propargylic Sulfinates
Table 5. [2,3]Sigmatropic rearrangement via silver salts.
effectively performed in the presence of multiple
sources of silver cations. The more non-coordinating
the anion, the faster the reaction occurs. The process
is also able to occur in a zeolitic framework; there-
fore, the process can become more “green,” but at the
expense of reaction time. Studies on the chemistry
and further applications of allenic sulfones are cur-
rently underway and results will be reported in due
course.
Entry
AgX (3.5 mol%)
AgSbF6
Time
Yield [%]
1
2
3
4
5
6
7
8
<5 min
<15 min
<10 min
<15 min
30 min
3 h
12 h
15 h
15 h
6 h
100
100
100
99
100
98
a)
AgBF4
AgOTf
AgClO4
AgCO2CF3
AgNO3
Ag3PO4
AgOAc
Ag2CO3
AgF
Experimental Section
100
100
100
100
General Procedure
9
10
11
12
13
14
The propargylic sulfinate was dissolved in the solvent
(0.05M). The silver catalyst was added and the heterogene-
ous mixture was stirred at room temperature and monitored
by TLC. Upon complete conversion to the product, the cata-
lyst was removed by filtration [using a Sterilite nylon mem-
brane (0.2 mm, 47 mm) for the zeolite catalyst, or through
a short pad of Celite for the silver salts] and rinsed with di-
chloromethane. The zeolite catalyst was dried by aspiration
and then recovered by carefully scraping it from the mem-
brane; traces remained adsorbed to the membrane and pre-
vented complete recovery. The filtrate was concentrated on
a rotary evaporator and trace solvent removed under high
vacuum to yield the allenic sulfone.
[b]
AgBr
AgI
AgCN
24 h
24 h
24 h
24 h
–
–
–
–
[c]
[d]
[e]
Ag2SO4
AgX (2 mol%)
AgSbF6
15
16
17
18
19
<1 min
2 min
3 min
6 min
50 min
99
99
99
100
98
[a]
AgBF4
AgOTf
AgClO4
AgCO2CF3
[a]
The reagent was deliquesced.[17]
5% conversion to product.
5% conversion to product.
7% conversion to product.
7% conversion to product.
[b]
[c]
[d]
[e]
Acknowledgements
conversion to the allenes, but still resulted in excellent
yields.
This work was supported by the National Science Foundation
and the Department of Chemistry at the University of Mis-
souri–Columbia. We thank Professor Patrick Pale (Universitꢀ
de Strasbourg) for a gift of his zeolite catalyst.
After a detailed examination of the catalytic activi-
ty of the Ag1-USY on the [2,3]sigmatropic rearrange-
ment of propargylic sulfinates, we decided to compare
the activity of other silver(I) salts as well. The results
are seen in Table 5. Strongly non-coordinating silver
salts resulted in very rapid reaction times (entries 1–
5). Less active catalysts were silver fluoride, nitrate,
phosphate, acetate, and carbonate, which required
longer times but still gave excellent yields of the al-
lenic sulfone (Table 5, entries 6–10). Salts such as
silver bromide, iodide, cyanide, and sulfate were inef-
fective at catalyzing the rearrangement in dichlorome-
thane (Table 5, entries 11–14). The five most reactive
silver salts were reduced in catalyst loading to
2 mol% and subjected to a careful evaluation of the
reaction time (Table 5, entries 15–19) The previously
reported silver hexafluoroantimonate effected an es-
sentially instantaneous reaction, followed very closely
by silver tetrafluoroborate, trifluoromethanesulfonate,
and perchlorate, all reactions being complete within
6 min. The trifluoroacetate salt required a slightly
longer reaction time of 50 min.
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Adv. Synth. Catal. 0000, 000, 0 – 0
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[17] The inital silver tetrafluoroborate sample that was used
was deliquesced (Table 5, entries 2 and 16). The rear-
rangement proceeded very quickly and was complete
in 2 min. To ensure that any adsorbed water on the
silver salt was not contributing to the rate of reaction,
a new bottle of AgBF4 was purchased and the [2,3]sig-
matropic rearrangement was performed with the new
dry sample. The reaction was monitored by TLC every
minute and was completed within 2 min and yielded
the allenic sulfone in 97% yield. To learn the effect of
water on the reaction, 0.6 equivalents (10 mL) of water
was added to the AgBF4 (2 mol%) in dichloromethane
(9 mL, 0.1M) and stirred. Then the sulfinate ester was
added to the flask and the reaction mixture was stirred
at room temperature, monitoring by TLC every
minute. This reaction required 8 min to achieve com-
plete conversion and resulted in a 96% yield of the al-
lenic sulfone.
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4
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Adv. Synth. Catal. 0000, 000, 0 – 0
ÝÝ
These are not the final page numbers!

UPDATES
[2,3]Sigmatropic Rearrangement of Propargylic Sulfinates
by a Pale Ag1-USY Zeolite and Silver Salts
5
Adv. Synth. Catal. 2015, 357, 1 – 5
Carissa S. Hampton, Michael Harmata*
Adv. Synth. Catal. 0000, 000, 0 – 0
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
5
ÞÞ
These are not the final page numbers!