By-Product-Catalyzed Redox-Neutral Sulfenylation/Deiodination/Aromatization of Cyclic Alkenyl Iodides with Sulfonyl Hydrazides

Article abstract of DOI:10.1002/adsc.201600795

A by-product-catalyzed redox-neutral process has been established through tandem sulfenylation/deiodination/aromatization of cyclic alkenyl iodides with sulfonyl hydrazides. In the absence of external catalysts and additives a range of 4-iodo-1,2-dihydronaphthalenes reacted with sulfonyl hydrazides to give structurally diverse 2-naphthyl thioethers in good yields. Mechanistic studies showed that at an early stage sulfonyl hydrazides decomposed completely to thiosulfonates and disulfides and at a late stage the resulting thiosulfonates underwent tandem sulfenylation/deiodination/aromatization with 4-iodo-1,2-dihydronaphthalenes involving a [1,5]-sigmatropic hydrogen shift. Importantly, iodine was generated as a by-product from 4-iodo-1,2-dihydronaphthalenes upon heating and served as a catalyst for the decomposition of sulfonyl hydrazides and subsequent formation of 2-naphthyl thioethers. (Figure presented.).

Full text of DOI:10.1002/adsc.201600795

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DOI: 10.1002/adsc.201600795
By-Product-Catalyzed Redox-Neutral Sulfenylation/Deiodination/
Aromatization of Cyclic Alkenyl Iodides with Sulfonyl Hydra-
zides
Fu-Lai Yang,a Yang Gui,a Bang-Kui Yu,a You-Xiang Jin,a and Shi-Kai Tiana,*
a
Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, Peopleꢀs Republic of
China
Fax : (+86)-551-6360-1592; e-mail: tiansk@ustc.edu.cn
Received: July 22, 2016; Revised: August 25, 2016; Published online: && &&, 0000
Supporting information for this article can be found under: http://dx.doi.org/10.1002/adsc.201600795.
Abstract:
A
by-product-catalyzed redox-neutral
although the valency of sulfur decreases from +6 to
+2.[1e,p] The reason behind this is that the NHNH2
group of the sulfonyl hydrazide can reduce the SO2
group to yield water and nitrogen as by-products. In
the course of extending the chemistry of sulfonyl hy-
drazides to alkenyl iodides, we unexpectedly discov-
ered a by-product-catalyzed redox-neutral process of
sulfenylation/deiodination/aromatization in the ab-
sence of any external catalysts and additives.
Initially, we employed 10 mol% iodine to catalyze
the reaction between cyclic alkenyl iodide 1a and sul-
fonyl hydrazide 2a aiming at an access to vinyl thio-
ether 3a (Scheme 1). The reaction proceeded in
chloroform under air in a sealed tube at 908C (oil
bath), and to our surprise, 2-naphthyl thioether 4a
rather than vinyl thioether 3a was obtained in 73%
yield. We next carried out a control experiment by
heating the mixture of cyclic alkenyl iodide 1a and
sulfonyl hydrazide 2a in chloroform. Unexpectedly,
the reaction furnished 2-naphthyl thioether 4a in
a comparable yield (71%). The fact that the original
colorless mixture turned dark purple as the reaction
progressed suggested the formation of iodine, which
was confirmed by potassium iodide-starch test papers.
Moreover, the mixture was detected to be acidic by
pH test papers and further detection with starch test
papers suggested the formation of HI and HI3 (gener-
process has been established through tandem sulfe-
nylation/deiodination/aromatization of cyclic alken-
yl iodides with sulfonyl hydrazides. In the absence
of external catalysts and additives a range of 4-
iodo-1,2-dihydronaphthalenes reacted with sulfonyl
hydrazides to give structurally diverse 2-naphthyl
thioethers in good yields. Mechanistic studies
showed that at an early stage sulfonyl hydrazides
decomposed completely to thiosulfonates and disul-
fides and at a late stage the resulting thiosulfonates
underwent tandem sulfenylation/deiodination/aro-
matization with 4-iodo-1,2-dihydronaphthalenes in-
volving a [1,5]-sigmatropic hydrogen shift. Impor-
tantly, iodine was generated as a by-product from 4-
iodo-1,2-dihydronaphthalenes upon heating and
served as a catalyst for the decomposition of sulfo-
nyl hydrazides and subsequent formation of 2-naph-
thyl thioethers.
Keywords: alkenyl iodides; by-product catalysis;
[1,5]-hydrogen shifts; sulfonyl hydrazides; thioeth-
ers
The employment of sulfonyl hydrazides as sulfenylat- ated from HI and iodine). These results encouraged
ing agents has recently emerged as a powerful strat-
egy for the preparation of thioethers through carbon-
sulfur bond-forming reactions.[1] In contrast to tradi-
tional sulfenylating agents such as thiols, disulfides,
sulfenyl halides, and sulfenamides, sulfonyl hydrazides
are much more amenable to manipulation in that
they are readily accessible and stable solids, free of
unpleasant odor, and compatible with water and air.
In this regard, we have established that iodine is able
to catalyze the sulfenylation of alkenes with sulfonyl
hydrazides, wherein no external reductant is required hydrazide 2a.
Scheme 1. Reaction of cyclic alkenyl iodide 1a with sulfonyl
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us to develop a tandem process of sulfenylation/deio- to the control experiment performed under nitrogen,
dination/aromatization, which would be catalyzed by which gave a 70% yield. On the other hand, perform-
iodine by-product.[2–4]
ing the reaction under oxygen led to a comparable
A set of conditions was examined for the reaction yield (68%). These results suggest that the reaction
of cyclic alkenyl iodide 1a with sulfonyl hydrazide 2a does not require the presence of oxygen. Neverthe-
in the absence of any external catalysts and additives. less, we decided to carry out the reaction under air
Significantly lower yields were achieved when replac- simply because of manipulative convenience.
ing chloroform with 1,2-dichloroethane (60%) or ace-
Cyclic alkenyl iodide 1a smoothly underwent
tonitrile (17%) and even no desired product was iso- tandem sulfenylation/deiodination/aromatization with
lated from the reaction performed in carbon tetra- a range of aromatic and aliphatic sulfonyl hydrazides
chloride, toluene, dioxane, nitromethane, N,N-dime- in the absence of any external catalysts and additives
thylformamide, dimethyl sulfoxide, ethanol, or acetic and the corresponding 2-naphthyl thioethers were ob-
acid. The oxygen in air proved unnecessary according tained in good yields (Table 1, entries 1–13). Either
Table 1. Sulfenylation/deiodination/aromatization of cyclic alkenyl iodides with sulfonyl hydrazides.[a]
Entry
1
R1
2
R2
4
Yield [%][b]
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1b
1c
1d
1e
1f
1g
1h
1i
H
H
H
H
H
H
H
H
H
H
H
H
H
1-Me
1-(3,4-Cl2C6H3)
1-(2-FC6H4)
2-Ph
3-CHPh2
6-OMe
6-Cl
2a
2b
2c
2d
2e
2f
2g
2h
2i
4-MeC6H4
Ph
4-Me3CC6H4
4-MeOC6H4
4-FC6H4
4-ClC6H4
4-BrC6H4
4-IC6H4
3-O2NC6H4
2,4,6-Me3C6H2
2-naphthyl
Me(CH2)7
Me(CH2)15
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
4a
4b
4c
4d
4e
4f
4g
4h
4i
71
74
70
65
72
67
63
56
53
63
68
63
58
64
54
56
84
–
54
73
68
47
71
71
61
–
9
10
11
12
13
14
15[c]
16[c]
17
18[d]
19
20
21
22
23
24
25[e]
26[d]
27[d]
2j
2k
2l
4j
4k
4l
2m
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
4m
4n
4o
4p
6e
–
4q
4r
4s
4t
6-Br
1j
1k
1l
1m
1a’
5
7-OMe
7-OTs
7-Cl
8-OMe
–
4u
4v
4w
–
Ph
Ph
–
–
–
[a]
Reaction conditions: 1 (0.20 mmol), 2 (0.27 mmol), chloroform (0.30 mL), under air in a sealed tube at 908C (oil bath) for
5 h (For entries 7–9, 10 h; For entries 12 and 13, 8 h).
Isolated yield.
The reaction was run at 1108C (oil bath) for 8 h.
No reaction was observed.
2 (0.54 mmol) was used.
[b]
[c]
[d]
[e]
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electron-donating or electron-withdrawing groups odination under the standard conditions to furnish
were successfully introduced into the diaryl thioether aryl iodide 6a and alkene 7a, respectively, the conver-
products from the corresponding aromatic sulfonyl sion was only 3% in two hours. Moreover, sulfonyl
hydrazides. On the other hand, a variety of cyclic al- hydrazide 2a was able to reduce alkene 7a in the pres-
kenyl iodides exhibited varied levels of reactivity ence of 10 mol% iodine to furnish tetrahydronaphtha-
under the standard reaction conditions (Table 1, en- lene 8a. On the other hand, sulfonyl hydrazide 2a de-
tries 14–26). While the desired reaction worked well composed completely in two hours to furnish a 70:30
with a 1-substituted 4-iodo-1,2-dihydronaphthalene, mixture of thiosulfonate 9a and disulfide 10a. In the
a 2-substituted one directly underwent aerobic oxida- third hour, alkenyl iodide 1a and intermediate 9a
tive dehydrogenation to furnish an aryl iodide in were completely consumed to furnish thioether 4a as
a good yield, probably owing to the steric repulsion in the major product and aryl iodide 6a as a minor prod-
the sulfenylation step (Table 1, entries 14–17).[5] As uct (Table 2, entry 3). Meanwhile, alkene 7a was com-
expected, no reaction was observed with a 3-substitut- pletely converted to tetrahydronaphthalene 8a and
ed 4-iodo-1,2-dihydronaphthalene (Table 1, entry 18). a small amount of thiosulfonate 9a was converted to
The tandem sulfenylation/deiodination/aromatization disulfide 10a, which, clearly, did not serve as an inter-
was successfully extended to a number of 4-iodo-1,2- mediate for the formation of thioether 4a.
dihydronaphthalenes having various substituents on
Simply heating the mixture of alkenyl iodide 1a
the benzene ring (Table 1, entries 19–24). Notably, and thiosulfonate 9a in chloroform failed to furnish
bissulfenylation was observed with high regioselectivi- thioether 4a, which, however, was obtained in a mod-
ty when the C-8 position of a 4-iodo-1,2-dihydronaph- erate yield after addition of 10 mol% iodine (Table 3,
thalene was occupied by an electron-donating group, entries 1 and 2). These results substantially demon-
such as the methoxy group (Table 1, entry 25).[1v] In strate that iodine, the afore-mentioned by-product
sharp contrast, no reaction took place either with al- generated from the reaction of alkenyl iodides with
kenyl iodide 1a’, an isomer of alkenyl iodide 1a, or sulfonyl hydrazides, serves as a catalyst for the
with alkenyl bromide 5 under the standard conditions tandem process of sulfenylation/deiodination/aromati-
(Table 1, entries 26 and 27).
zation. In sharp contrast, similar reactions with disul-
To gain insights into the reaction mechanism, we fide 10a furnished an inseparable mixture of thioether
1
carried out a H NMR spectroscopic analysis of the 4a and its isomer 4a’ (Table 3, entries 3 and 4), which,
reaction mixture of alkenyl iodide 1a with sulfonyl hy- however, was not detected in the reaction of alkenyl
drazide 2a in deuterated chloroform and found that iodide 1a with sulfonyl hydrazide 2a. These results
both substrates were subjected to decomposition in further confirmed that disulfide 10a did not serve as
the first two hours (Table 2, entries 1 and 2). On one an intermediate for the formation of thioether 4a.
hand, 19% of alkenyl iodide 1a was converted to aryl
To determine the hydrogen source that formally
iodide 6a, alkene 7a, and tetrahydronaphthalene 8a, displaced the iodine atom, we carried out the follow-
whose structure was further confirmed by high resolu- ing deuterium-labelling experiments (Scheme 2).
tion mass spectrometric analysis.[6] Although alkenyl Treatment of thiosulfonate 9j with monodeuterated
iodide 1a underwent oxidative aromatization and dei- alkenyl iodide 1a-D1 in deuterated chloroform did
Table 2. 1H NMR spectroscopic analysis of the reaction mix-
ture.
Table 3. Transformations of intermediates.[a]
Entry
[S]
Catalyst
Yield [%][b]
4a:4a’[c]
1
2
3
4
9a
9a
10a
10a
none
I2 (10 mol%)
none
0
–
46
46
50
>99:1
39:61
60:40
I2 (10 mol%)
[a]
Reaction conditions: 1a (0.20 mmol), [S] (0.135 mmol),
catalyst (if any), chloroform (0.30 mL), under air in
a sealed tube at 908C (oil bath) for 5 h.
Isolated yield.
[b]
[c]
1
Determined by H NMR spectroscopic analysis.
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Scheme 2. Deuterium-labelling experiments.
Scheme 3. Proposed major reaction pathways.
not result in deuterium incorporation into thioether shift occurs to generate alkene 15,[11] from which elim-
4j. In contrast, a similar reaction with polydeuterated ination of HI gives thioether 4.
alkenyl iodide 1a-D9 furnished thioether 4j-D7 with
In summary, we have developed, for the first time,
45% deuterium incorporation at C-4. These results, an efficient by-product-catalyzed redox-neutral pro-
along with the fact that the percentage of deuterium cess through tandem sulfenylation/deiodination/aro-
increased slightly at C-2, suggest that a hydrogen/deu- matization of cyclic alkenyl iodides with sulfonyl hy-
terium shift occurred from C-2 to C-4. The level of drazides. A range of 4-iodo-1,2-dihydronaphthalenes
deuterium incorporation at C-4 in thioether 4j-D7 smoothly reacted with sulfonyl hydrazides in the ab-
was much lower than the percentage of deuterium at sence of any external catalysts and additives to give
C-2 in alkenyl iodide 1a-D9 simply due to hydrogen/ structurally diverse 2-naphthyl thioethers in good
deuterium exchange with the moisture in the air yields. Mechanistic studies showed that at an early
under the standard conditions. The hydrogen/deuteri- stage sulfonyl hydrazides decomposed completely to
um exchange was confirmed by the following experi- thiosulfonates and disulfides and at a late stage the
ment. Treatment of thioether 4j with one equivalent resulting thiosulfonates underwent tandem sulfenyla-
of HI and ten equivalents of deuterated water fur- tion/deiodination/aromatization with 4-iodo-1,2-dihy-
nished thioether 4j-D1 with deuterium incorporation dronaphthalenes involving a [1,5]-sigmatropic hydro-
exclusively at the a-position.
gen shift. Importantly, iodine was generated as a by-
Based on the above experimental results and previ- product from 4-iodo-1,2-dihydronaphthalenes upon
ous relevant studies, we propose the following major heating and served as a catalyst for the decomposition
reaction pathways as depicted in Scheme 3 for the of sulfonyl hydrazides and subsequent formation of 2-
tandem process of sulfenylation/deiodination/aromati- naphthyl thioethers.
zation. At an early stage, alkenyl iodide 1 decomposes
upon heating to generate small amounts of aryl iodide
6, alkene 7, iodine, and HI. Alkene 7 is reduced by
sulfonyl hydrazide 2 to give by-product 8.[7] While the
Experimental Section
decomposition of sulfonyl hydrazide 2 to sulfinic acid
12 can take place upon heating,[8,9] the iodine by-prod-
General Procedure for the Sulfenylation/
Deiodination/Aromatization of Cyclic Alkenyl
uct dramatically accelerates this process.[1a,e,p] Reduc-
tion of sulfinic acid 12 occurs either with sulfonyl hy-
drazide 2 or with HI, and a small portion of the re-
sulting thiosulfonate 9 is further reduced to give disul-
fide 10 as another by-product.[1p] Thiosulfonate 9 is
activated by iodine and undergoes regioselective elec-
trophilic addition to alkenyl iodide 1 to generate car-
bocation 13,[10] deprotonation of which gives dihydro-
naphthalene 14. Then a [1,5]-sigmatropic hydrogen 4.
Iodides with Sulfonyl Hydrazides
To a solution of sulfonyl hydrazide 2 (0.27 mmol) in chloro-
form (0.30 mL) was added alkenyl iodide 1 (0.20 mmol).
The mixture was heated at 908C (oil bath) under air in
a sealed tube for 5 h, cooled to room temperature, and puri-
fied by silica gel column chromatography, eluting with ethyl
acetate/petroleum ether (0:10 to 1:10 v/v), to give thioether
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of alkenyl iodide 1a with sulfonyl hydrazide 2a
(Table 2). This suggests that the conversion of sulfonyl
hydrazide 2 to sulfinic acid 12 is much faster than that
of sulfinic acid 12 to thiosulfonate 9. In addition, we
treated sulfinic acid 12a with alkenyl iodide 1a under
the standard conditions and obtained thioether 4a in
57% yield.
Acknowledgements
We are grateful for the financial support from the National
Natural Science Foundation of China (21472178, 21232007,
and 21502182), the National Key Basic Research Program of
China (2014CB931800), the Strategic Priority Research Pro-
gram of the Chinese Academy of Sciences (XDB20000000),
FRFCU (WK2060190048), and China Postdoctoral Science
Fundation (2015M571937).
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X.-P. Zeng, in: Multicatalyst System in Asymmetric Cat-
alysis, (Ed.: J. Zhou), John Wiley & Sons, New York,
2015, pp 633–670. For examples, see: b) T.-P. Loh, K.-T.
Tan, Q.-Y. Hu, Tetrahedron Lett. 2001, 42, 8705–8708;
c) K.-T. Tan, S.-S. Chng, H.-S. Cheng, T.-P. Loh, J. Am.
Chem. Soc. 2003, 125, 2958–2963; d) H.-H. Li, D.-J.
Dong, S.-K. Tian, Eur. J. Org. Chem. 2008, 3623–3626;
e) P. J. Alaimo, R. OꢀBrien III, A. W. Johnson, S. R.
Slauson, J. M. OꢀBrien, E. L. Tyson, A.-L. Marshall,
Adv. Synth. Catal. 0000, 000, 0 – 0
5
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
These are not the final page numbers!

COMMUNICATIONS
6 By-Product-Catalyzed Redox-Neutral Sulfenylation/
Deiodination/Aromatization of Cyclic Alkenyl Iodides with
Sulfonyl Hydrazides
Adv. Synth. Catal. 2016, 358, 1 – 6
Fu-Lai Yang, Yang Gui, Bang-Kui Yu, You-Xiang Jin,
Shi-Kai Tian*
Adv. Synth. Catal. 0000, 000, 0 – 0
6
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
These are not the final page numbers!