Rhodium(II)-Catalyzed and Thermally Induced Intramolecular Migration of N-Sulfonyl-1,2,3-triazoles: New Approaches to 1,2-Dihydroisoquinolines and 1-Indanones

Article abstract of DOI:10.1002/chem.201504914

New rhodium(II)-catalyzed or thermally induced intramolecular alkoxy group migration of N-sulfonyl-1,2,3-triazoles has been developed, affording divergent synthesis of 1,2-dihydroisoquinoline and 1-indanone derivatives according to different conditions. N-Sulfonyl keteneimine is the key intermediate for the synthesis of dihydroisoquinoline, whereas the aza-vinyl carbene intermediate results in the formation of 1-indanone.

Full text of DOI:10.1002/chem.201504914

DOI: 10.1002/chem.201504914
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&
Synthetic Methods
Rhodium(II)-Catalyzed and Thermally Induced Intramolecular
Migration of N-Sulfonyl-1,2,3-triazoles: New Approaches to
1,2-Dihydroisoquinolines and 1-Indanones
Run Sun,[a] Yu Jiang,[a] Xiang-Ying Tang,*[b] and Min Shi*[a, b]
Abstract: New rhodium(II)-catalyzed or thermally induced in-
tramolecular alkoxy group migration of N-sulfonyl-1,2,3-tri-
azoles has been developed, affording divergent synthesis of
1,2-dihydroisoquinoline and 1-indanone derivatives accord-
ing to different conditions. N-Sulfonyl keteneimine is the key
intermediate for the synthesis of dihydroisoquinoline, where-
as the aza-vinyl carbene intermediate results in the forma-
tion of 1-indanone.
Introduction
In recent years, N-sulfonyl-1,2,3-triazoles, which can easily be
prepared from copper(I)-catalyzed azide–alkyne cycloadditions,
have emerged as stable and readily available precursors of a-
imino metal carbenes.[10] Thus far, it has been known that they
can undergo a variety of synthetically useful transformations
through typical carbene reaction manners[11] such as cyclopro-
panation,[12] CÀH, OÀH, or NÀH insertion,[13] transannulation,[14]
and other types of rhodium carbene-based reactions.[15] Fur-
thermore, ether could also be used as nucleophiles to a-imino
metal carbene. For example, Yang’s group discovered that tria-
zoles bearing allylic ether groups would perform an intramo-
lecular [2,3]-sigmatropic rearrangement after nucleophilic
attack of oxygen atom, in which the distal CÀO bond cleavage
occurred (Scheme 1).[15j,k,m] Surprisingly, during our ongoing in-
vestigation on the ring opening of N-sulfonyl triazoles, we
found that substrates 1 underwent an alkoxy group migration,
in which the proximal CÀO bond was cleaved.[15k] Herein, we
wish to report an unprecedented condition-controlled reaction
of N-sulfonyl-1,2,3-triazoles, in which substituted 1,2-dihydroi-
soquinoline and 1-indanone derivatives could be furnished
through alkoxy group migration (Scheme 1).
The 1,2-dihydroisoquinoline core[1] and 1-indanone core[2] rep-
resent privileged structures encountered in many natural prod-
ucts, as well as molecules exhibiting promising bioactivities.
The indane ring system also has distinguished utility in dyes,
organic light-emitting devices, and photoremovable protecting
groups.[3] Hence, a variety of synthetic methods have been de-
veloped towards their synthesis. The 1,2-dihydroisoquinoline
structure can be usually synthesized through two different ap-
proaches: functionalization of the parent isoquinoline and de
novo synthesis of the 1,2-dihydroisoquinoline. Reissert-type re-
actions and selective reduction are mostly used in the first ap-
proach.[4] Variations of 6-endo-dig cyclization of preformed or in
situ-generated ortho-alkynylaryl aldimines and other strategies
including the Larock dihydroisoquinoline synthesis have been
developed for the second approach.[5,6] On the other hand, in-
tramolecular Friedel–Crafts reaction[7] and Nazarov cyclization[8]
are frequently used for the synthesis of indanones. Moreover,
several other methods including RhI-catalyzed isomerization
have also been developed.[9] Due to their significant synthetic
utility and application in pharmaceuticals, the development of
new synthetic methods for the synthesis of 1,2-dihydroisoqui-
noline and 1-indanone derivatives is still highly desired.
Results and Discussion
Using 1a as a model substrate, we commenced our investiga-
tion by treating it with [Rh2(esp)2] (esp=a,a,a’,a’-tetramethyl-
1,3-benzenedipropionic acid) in toluene at different tempera-
tures in a sealed tube; the corresponding 1,2-dihydroisoquino-
line derivative 3a was best obtained in 33% yield at 808C
(Table 1, entries 1–3). Screening of rhodium(II) catalysts demon-
strated that [Rh2(esp)2] was the best catalyst for the synthesis
of 3a, whereas upon prolonged reaction time other catalysts
such as [Rh2(OAc)4] also led to 2a, a regioisomer of 3a (Table 1,
entries 4–6, see the Supporting Information for more details).
We realized afterwards that the reaction of 1a to produce 2a
was a thermally induced rearrangement, so that the formation
of 2a may be the result of low activity of the responding cata-
lyst.[16,17] Next, the solvent effect was tested; it was found that
[a] R. Sun, Y. Jiang, Prof. Dr. M. Shi
Key Laboratory for Advanced Materials and Institute of Fine Chemicals,
East China University of Science and Technology
Meilong Road No. 130, Shanghai
200237 (China)
[b] Prof. Dr. X.-Y. Tang, Prof. Dr. M. Shi
State Key Laboratory of Organometallic Chemistry
Shanghai Institute of Organic Chemistry
Chinese Academy of Sciences
345 Lingling Road, Shanghai
200032 (China)
E-mail: siocxiangying@mail.sioc.ac.cn
mshi@mail.sioc.ac.cn
Supporting information for this article can be found under http://
dx.doi.org/10.1002/chem.201504914.
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Scheme 1. Reactions of a-imino rhodium carbenes and ether.
Table 1. Optimization of the reaction conditions.
Entry[a]
Catalyst
Solvent
T
[oC]
Yield
[%]
d.r. of
4a[b]
2a
3a
4a
1
2
3
4
5
6
7
8
[Rh2(esp)2]
[Rh2(esp)2]
[Rh2(esp)2]
[Rh2(Piv)4]
[Rh2(OAc)4]
[Rh2(oct)4]
–
–
–
–
–
[Rh2(esp)2]
[Rh2(esp)2]
[Rh2(esp)2]
[Rh2(esp)2]
[Rh2(esp)2]
[Rh2(esp)2]
toluene
toluene
toluene
toluene
toluene
toluene
toluene
DCE
110
80
60
80
80
80
80
80
80
80
80
80
80
80
80
80
80
trace
trace
trace
trace
20
trace
9
68
70
trace
83
36
68
28
33
30
31
7
30
–
–
trace
trace
trace
trace
trace
trace
–
–
–
–
–
trace
trace
trace
22
50
57
–
–
–
–
–
–
–
–
–
–
–
–
–
–
14:1
11:1
19:1
9
MeCN
–
–
–
10
11
12
13
14
15[c]
16[d]
17[e]
cyclohexane
ClCH2CN
DCE
trace
trace
20
33
23
15
MeCN
cyclohexane
toluene
toluene
toluene
trace
trace
trace
trace
[a] Reaction conditions: compound 1a (0.2 mmol) and catalyst (0.004 mmol) were combined and heated in specified solvent (1 mL) at specified tempera-
1
ture for 4–48 h in a sealed tube. [b] Diastereomeric ratio (d.r.) determined by H NMR analysis of the crude residue. [c] 3 mL of solvent was used. [d] Com-
pound 1a was added by injection pump to a solution of the catalyst (1.0 mL) in a Schlenk tube in 6 h. [e] Reaction was carried out under open air. esp=
a,a,a’,a’-tetramethyl-1,3-benzenedipropionic acid, Piv=pivalate, oct=octanoate, DCE=1,2-dichloroethane.
2a could be afforded exclusively in 83% yield in ClCH2CN,
whereas toluene remained to be the best solvent for the for-
mation of 3a. This suggests that a polar solvent favors the for-
mation of 2a over 3a (Table 1, entries 7–14). To improve the
yield of 3a, we next tried to conduct the reaction in diluted
toluene and found that 1-indanone derivative 4a was obtained
with good diastereoselectivity, and its configuration has been
unambiguously determined by the X-ray crystal structure
(Table 1, entry 15).[18] By adding 1a into the solution of
[Rh2(esp)2] with an injection pump over 6 h, compounds 3a
and 4a were afforded in 23 and 50% yields, respectively
(Table 1, entry 22). Considering that ambient water may be in-
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volved in the reaction, the reaction was then carried out under
open air. To our delight, compound 4a was obtained in 57%
yield with good diastereoselectivity (19:1) (Table 1, entry 17).
With optimal reaction conditions in hand, we first surveyed
the substrate scope of the thermally induced rearrangement of
1 (Table 2). Other N-protecting groups such as 4-bromobenze-
nesulfonyl (Bs) and methylsulfonyl (Ms) were well compatible
and the corresponding products 2b and 2c were obtained in
71 and 54% yields, respectively. For substrate 1d with ethoxy
instead of methoxy, the reaction gave the desired product 2d
in moderate yield, perhaps due to increased steric hindrance.
Substrates with electron-donating groups (R3 or R4) led to rela-
tively higher yields (2 f–2g, 2k–2m) than those with electron-
withdrawing ones (2h–2j, 2n), suggesting that a cationic inter-
mediate may be formed during the reaction process. In addi-
tion, R4 could be extended to vinyl or naphthyl groups and the
reactions delivered the corresponding products 2o and 2p in
45 and 75% yields. The reaction was sluggish upon changing
R4 to a furyl ring, and the corresponding product 3q was ob-
tained only in 14% yield.
and 2). Substrates with a larger steric hindrance on the oxygen
atom suffered lower efficiency and diastereoselectivity (Table 3,
entries 3 and 4). It should be noted that BnOH was detected in
the system when 1e was used as the substrate.[19] The elec-
tronic effect (R3 and R4) was also investigated. Generally, elec-
tron-rich substrates resulted in better reaction outcomes than
those electron-deficient substrates (Table 3, entries 5–14). In
particular, substrate 1j bearing a fluorine atom on R3 was less
reactive under the standard conditions, and only a trace of the
1
corresponding product was detected by H NMR spectroscopy
when the reaction was carried out at even higher temperature
(Table 3, entry 10). Substrates with a naphthalene ring, furyl
ring, or vinyl group were also tolerated in the reaction (Table 3,
entries 15 and 16). For substrate 1t, which bears methyl group
as R4, the corresponding products 3t could be furnished as the
only product under more meticulous conditions, whereas the
standard conditions resulted in complex mixtures (Table 3, en-
tries 18). Interestingly, using thiophene-based triazole 1r as
substrate, the corresponding product 4r could be obtained ex-
clusively in 39% yield along with good diastereoselectivity
(Table 3, entry 19). All these cyclized products 3 and 4 could
easily be separated by silica gel flash-column chromatography
or preparative thin layer chromatography (PTLC).
Next, we turned our effort to investigate the substrate scope
of the rhodium(II)-catalyzed rearrangement of N-sulfonyl tria-
zoles 1 (Table 3). Substrates with Bs and Ms N-protecting
groups were suitable in this reaction, giving the desired prod-
ucts in 46 and 63% total yields, respectively (Table 3, entries 1
To investigate the mechanisms of these reactions, several
deuterium labeling experiments were conducted.[19] By adding
D2O into the thermally induced reaction, the corre-
sponding deuterated product [D]-2a was obtained
Table 2. Reaction scope: Thermally induced rearrangement.[a]
(Scheme 2a). For the rhodium-catalyzed reaction, no
deuterium incorporation was observed in all the iso-
lated products due to the proton exchange in silica
gel chromatography during the purification, where-
as the deuterium-labeled product [D]-4a could be
1
detected by H NMR spectroscopy of the crude reac-
tion residue (Scheme 2b). For substrate [D]-1a, the
thermal-induced rearrangement reaction gave the
corresponding deuterated product [D]-2a, indicating
that a 1,2-H shift takes place in the reaction process
(Scheme 2c). In the rhodium-catalyzed reaction of
[D]-1a, the deuterated product [D]-3a was obtained
together with 4a (Scheme 2d).
Based on the above results and the previously re-
ported literature,[11–17] plausible mechanisms for
these reactions have been proposed using 1a as
a model substrate in Schemes 3 and 4, respectively.
As illustrated in Scheme 3, the thermally induced
transformation begins with rapid denitrogenation of
the N-sulfonyl triazole 1a, affording carbene inter-
mediate A, which then induces a 1,2-H shift to give
ketenimine intermediate A’. As shown in path a, the
methoxy group may attack the imino carbon to
form intermediate B. The following ring opening
and rearrangement give the corresponding zwitter-
ionic intermediate C and its resonanced intermedi-
ates C’ and C’’, in which the carbocation could be
stabilized by the adjacent aromatic rings. The subse-
[a] Reaction conditions: Under argon, 1 (0.2 mmol) was heated in ClCH2CN (2 mL) in
a sealed tube at 80oC for 12–24 h. Yields are isolated yields of purified products.
quent cyclization gives product 2a. Alternatively, ke-
tenimine A can also undergo a 1,5-OMe shift to give
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Table 3. Reaction scope: Rhodium(II)-catalyzed rearrangement.
Entry[a]
Substrate
R1
R2
R3
R4
Yield[b]
[%]
d.r. of
4a[c]
3
4
Total
1[d]
2
3
4
5
6
7[d]
8
1b
1c
1d
1e
1 f
1g
1s
1h
1i
1j
1k
1l
1m
1n
1p
Bs
Ms
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Me
Me
Et
–
–
–
–
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
12
19
26
10
16
9
34
44
45
28
57
49
44
19
27
–
43
47
32
38
50
46
63
61
38
73
58
53
38
41
–
65
56
51
44
61
8:1
11:1
8:1
10:1
19:1
>20:1
>20:1
7:1
7:1
–
12:1
18:1
15:1
8:1
Bn
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
4-Me
5-Me
5-OMe
4-Cl
5-Br
6-F
–
–
-
–
–
9
19
14
–
22
9
19
6
11
9
Ph
Ph
10[e]
11
12
13
14
15[d]
2-MePh
3,5-di-tBuPh
4-MeOPh
4-ClPh
2-naph
12:1
16
1q
Ts
Me
–
4
22
26
13:1
17[f]
18[d,f]
1o
1t
Ts
Ts
Me
Me
–
–
vinyl
Me
11
30
46
–
57
30
7:1
–
19
–
–
–
–
–
39
39
15:1
1r
[a] Reaction conditions: Under open air, 1 (0.2 mmol), [Rh2(esp)2] (0.004 mmol) was heated in toluene (2 mL) at 80oC for 12 h. [b] Yields are isolated yields
1
of purified products. [c] Diastereoselectivity determined by H NMR analysis of the crude residue. [d] Reaction was carried out at 60oC. [e] Reaction was car-
ried out at 100oC. [f] Reaction was carried out under argon.
dienimine D. A subsequent 6p-electrocyclic ring closure (6p-
ERC) affords product 2a (path b).
danone derivatives through intramolecular alkoxy group mi-
gration pathway under thermally induced or Rh(II)-catalyzed
conditions. These new findings subsequently enrich the
chemistry of a-imino rhodium carbenes with oxygen nucleo-
philes. The reactions also provide new synthetic methods for
the valuable 1,2-dihydroisoquinoline and 1-indanone ring sys-
tems.
The rhodium(II)-catalyzed rearrangement mechanism is
shown in Scheme 4. The initial rhodium(II)-catalyzed denitroge-
nation of the N-sulfonyl triazole 1a gives the corresponding
rhodium(II) azavinyl carbene E, which undergoes nucleophilic
attack to afford a zwitterionic intermediate F. CÀO bond cleav-
age of F results in intermediate G, which is stabilized as a ben-
zylic cation. As shown in Table 3, the stability of the carbocat-
ion in intermediate G may greatly affect the formation of 4.
The final product 3a can be delivered after a ring-closing pro-
cess (path a). Alternatively, dearomatization of G is also possi-
ble and an imino intermediate H is obtained. The following
6p-ERC also gives rise to product 3a (path b). As for the forma-
tion of 4a, the activation of imino intermediate H by Rh(II) cat-
alyst as a Lewis acid generates intermediate I, from which in-
termediate J is formed through isomerization. Hydrolysis of J
furnishes the corresponding 1-indanone derivative 4a along
with the regeneration of the catalyst.
Experimental Section
General information and methods
Unless otherwise stated, all reactions and manipulations were per-
formed using standard Schlenk techniques. All solvents were puri-
fied by distillation using standard methods. Commercially available
reagents were used without further purification. Melting points
were determined on a digital melting point apparatus and temper-
atures were uncorrected. 1H and 13C NMR spectroscopic were re-
corded by using a Bruker AM-400 spectrometer in CDCl3 with tetra-
methylsilane (TMS) as an internal standard. 1H NMR and 13C NMR
chemical shift were referenced to d=0.00 (TMS) and 77.0 ppm
(CDCl3), respectively; coupling constants J are given in Hz. Infrared
spectroscopic were recorded on a PerkinElmer PE-983 spectrome-
ter with absorption in cmÀ1. Mass spectroscopic were recorded by
EI, ESI, MALDI and HRMS was measured on a HP-5989 instrument.
Conclusion
We have found that N-sulfonyl-1,2,3-triazoles bearing an alkoxy
group can furnish substituted 1,2-dihydroisoquinoline and 1-in-
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Scheme 2. Deuterium labeling experiments.
Scheme 3. Plausible mechanisms for thermally induced migration.
X-ray diffraction analysis was performed by using a Bruker Smart-
1000 or Bruker SMART APEXIIX-ray diffractometer. Flash column
chromatography was performed by using 300–400 mesh silica gel.
For thin-layer chromatography (TLC), silica gel plates (Huanghai
GF254) were used.
(monitored by TLC). The solvent was evaporated under reduced
pressure. The crude residue was purified by flash-column chroma-
tography on a silica gel eluting with petroleum ether and ethyl
acetate (v/v, 15:1 to 10:1) to afford the corresponding products 2.
General procedure for synthesis of 1,2-dihydroisoquinoline de-
rivative 3 and 1-indanone derivative 4: Compound 1 (0.2 mmol),
[Rh2(esp)2] (3 mg, 0.004 mmol), and toluene (2 mL) were added to
a Schlenk flask. The reaction mixture was stirred at 808C (or as indi-
cated) under air (or as indicated) until the reactant disappeared
General procedure for the synthesis of 1,2-dihydroisoquinoline
derivative 2: Compound 1 (0.2 mmol) and ClCH2CN (2 mL) were
added to a flame-dried sealed tube under argon. Then, the reac-
tion mixture was stirred at 808C until the reactant disappeared
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Acknowledgement
We are grateful for the financial support from the National
Basic Research Program of China (973)-2015CB856603, the Na-
tional Natural Science Foundation of China (20472096,
21372241, 21361140350, 20672127, 21421091, 21372250,
21121062, 21302203, 20732008 and 21572052).
Keywords: carbenes
rhodium · triazoles
·
heterocycles
·
rearrangement
·
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data for this paper. These data can be obtained free of charge from
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Received: December 7, 2015
Published online on March 2, 2016
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim