Rhodium-Catalyzed Denitrogenative [3+2] Cycloaddition: Access to Functionalized Hydroindolones and the Framework of Montanine-Type Amaryllidaceae Alkaloids

Article abstract of DOI:10.1002/chem.201702893

Rhodium-catalyzed denitrogenative [3+2] cycloaddition of 1-sulfonyl-1,2,3-triazoles with cyclic silyl dienol ethers has been developed for the synthesis of functionalized hydroindolones or their corresponding silyl ethers. The present method has been employed to construct synthetically valuable bicyclo[3.3.1]alkenone derivatives and pyrrolidine-ring-containing bicyclic indole compounds. As a further synthetic application, a stereoselective synthesis of 5,11-methanomorphanthridin-3-one, which shares a key skeleton with montanine-type Amaryllidaceae alkaloids has been achieved by using this chemistry.

Full text of DOI:10.1002/chem.201702893

A Journal of
Accepted Article
Title: Rhodium-Catalyzed Denitrogenative [3+2] Cycloaddition:
Access to Functionalized Hydroindolones and the Framework of
Montanine-Type Amaryllidaceae Alkaloids
Authors: Hongjian Yang, Shengtai Hou, Cheng Tao, Zhao Liu, Chao
Wang, Bin Cheng, Yun Li, and Hongbin Zhai
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To be cited as: Chem. Eur. J. 10.1002/chem.201702893
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Rhodium-Catalyzed Denitrogenative [3+2] Cycloaddition: Access
to Functionalized Hydroindolones and the Framework of
Montanine-Type Amaryllidaceae Alkaloids
Hongjian Yang,[a] Shengtai Hou,[a] Cheng Tao,[a] Zhao Liu,[a] Chao Wang,[a] Bin Cheng,[a] Yun Li*[a] and
Hongbin Zhai*[a,b,c]
Dedication ((optional))
Abstract: Rhodium-catalyzed denitrogenative [3+2] cycloaddition of
1-sulfonyl-1,2,3-triazoles with cyclic silyl dienol ethers to synthesize
functionalized hydroindolones or their corresponding silyl ethers has
been developed. The present method has been employed to
construct synthetically valuable bicyclo[3.3.1]alkenone derivatives
and pyrrolidine ring consisting bicyclic indole compounds. As a
further synthetic application, a stereoselective synthesis of 5,11-
methanomorphanthridin-3-one which shares the key skeleton with
Figure 1. Representative important natural products containing hydroindolone
scalfolds.
montanine-type Amaryllidaceae alkaloids has been achieved by
using this chemistry.
the preparation of synthetically valuable hydroindole derivatives
from steadily available 1-sulfonyl-1,2,3-triazoles and cyclic silyl
dienol ethers. Furthermore, the synthesis of 5,11-
Introduction
methanomorphanthridin-3-one which posseses a key skeleton of
montanine-type Amaryllidaceae alkaloids has also been
achieved by using the present synthetic protocol.
Hydroindoles and their derivatives are one of the most important
structural motifs prevalent in numerous biologically active
compounds and natural products such as mesembrine,[1]
herquiline,[2] and montanine-type Amaryllidaceae alkaloids[3]
(Figure 1). In this regard, development of a general and efficient
synthetic method to access this class of compounds from readily
available starting materials would greatly facilitate the total
synthesis of a large number of relevant natural products. To date,
several strategies have been employed to construct this
important scaffold, most commonly involving the hydrogenation
of indoles,[4] intermolecular reductive amination,[5] intramolecular
Michael addition,[6] etc.[7] However, most of these methods more
or less suffer from limitations, such as unsatisfactory
regioselectivity, poor accessibility of simple starting materials,
requirement of multiple-step operations, harsh conditions, and
so on. Herein, we report an efficient stereoselective method for
[a]
H. Yang, S. Hou, C. Tao, Z. Liu, C. Wang, B. Cheng, Y. Li, Prof. Dr.
H. Zhai
The State Key Laboratory of Applied Organic Chemistry, College of
Chemistry and Chemical Engineering, Lanzhou University
730000 (China)
Scheme 1. Rh-catalyzed transformations of triazoles with enol ethers (eq a),
2-(siloxy)furans (eq b) and terminal dienes (eq c).
E-mail: zhaihb@pkusz.edu.cn
liyun@lzu.edu.cn
[b]
[c]
Prof. Dr. H. Zhai
Recently, the rhodium-catalyzed cycloaddition reactions using
iminocarbene intermediates derived from 1-sulfonyl-1,2,3-
triazoles have been extensively explored in recent years.[8]
Laboratory of Chemical Genomics, School of Chemical Biology and
Biotechnology, Shenzhen Graduate School of Peking University
518055 (China)
Prof. Dr. H. Zhai
Collaborative Innovation Center of Chemical Science and
Engineering (Tianjin)
Based on the dipole feature of the in situ generated
α-
iminocarbene, an array of [3+2] cycloaddition reactions have
been developed by employing unsaturated compounds including
alkynes,[9] alkenes,[10] allenes,[11] isocyanides,[12] nitriles,[13]
aldehydes,[14] furans,[15] indoles[16] as the reaction counterparts to
300071 (China)
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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deliver the nitrogen-containing heterocycles.[17] More recently,
Tang, Lee, Anbarasan, Li, and Murakami groups have reported
that enol ethers (Scheme 1a) and 2-(siloxy)furans (Scheme 1b)
could react with 1-sulfonyl-1,2,3-triazoles in the presence of
rhodium catalysis to give pyrrole, lactam and dihydropyridine
derivatives.[15,18] Tang and co-workers have also described an
efficient synthesis of 2,5-dihydroazepines via formal aza-[3+2]
cycloadditions of triazoles with 1,3-dienes (Scheme 1c).[10g] Two
individual examples for preparation of dihydropyrrols by using
acyclic silyl dienol ethers as reaction counterparts have also
been described in their report. However, the reactivity and
diastereoselectivity of more steric hindered cyclic silyl dienol
ethers in the denitrogenative formal aza-[3+2] cycloadditions
have not been explored so far.
Considering the relative instability of silyl enol ether 3a, 3a was
converted into the more stable hydroindolone 4a in 55% overall
yield by simply adding trifluoroacetic acid to the reaction mixture
in the same pot. Catalyst screening (Table 1, entries 2-7)
revealed that Rh2(oct)4 was the optimal one to give 4a in 69%
isolated yield. The substrate ratio was then found to be
important for this reaction (Table 1, entries 2, 8, 10, see the
supporting information for details). The optimal yield of 4a was
obtained in 70% (Table 1, entry 8) with molar ratio 1a / 2a = 1:2
o
in the presence of 2 mol% of Rh2(oct)4 in DCE at 100 C. The
higher catalyst loading didn’t show any improvement to the yield
(entry 11). Noteworthily, the conversion could not be observed
o
under a temperature lower than 80 C (Table 1, entry 9). Other
condition optimizations including solvents and concentration
variation failed to give better results (Table 1, entries 12-14).[21]
A control experiment in the absence of rhodium catalyst (Table,
entry 15) gave none of desired product 3a or 4a while with
triazole 1a fully recovered.
Table 1. Optimization of the reaction conditions.
Scheme 2. Proposed mechanism for the rhodium-catalyzed [3+2]
cycloaddition
.
T
Yield
(%)[b]
Entry[a]
1a:2a
Rh2(L)n
Solvent
Inspired by these encouraging findings and combined with our
previous experience on denitrogenative intramolecular [3+2]
dipolar cycloaddition reactions,[16f] we speculate that, upon
treatment with suitable rhodium catalysts, the cyclic silyl dienol
ether 2a might function as a versatile nucleophile to trap the α-
iminocarbene intermediate A that in situ generated from 1-
sulfonyl-1,2,3-triazole 1a and lead to the cyclopropyl imine B
(Scheme 2). This resulting intermediate would be
rearranged[10h,15d] to form zwitterionic intermediate C which might
undergo an intramolecular aza-Michael addition to afford the silyl
enol ether 3a. Subsequential hydrolysis of 3a might deliver the
synthetically valuable bicyclic hydroindolone 4a.
(oC)
1
2
1:3
1:3
Rh2(OAc)4
Rh2(oct)4
DCE
DCE
110
110
55
69
3
1:3
1:3
1:3
1:3
1:3
1:2
1:2
2:1
1:2
1:2
1:2
1:2
1:2
Rh2(TFA)4
Rh2(esp)2
Rh2(piv)4
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE[e]
CHCl3
PhMe
DCE
110
110
110
110
110
100
80
45
4
55
5
67
6
Rh2(S-TBSP)4
Rh2(S-NTTL)4
Rh2(oct)4
63
7
63
8
70
NR[c]
9
Rh2(oct)4
10
11
12
13
14
15
Rh2(oct)4
100
100
100
100
100
100
50
[d]
Rh2(oct)4
61
Rh2(oct)4
Rh2(oct)4
Rh2(oct)4
-
61
Results and Discussion
55
61
NR[c]
To test our hypothesis, we first investigated the reaction of 4-
phenyl-1-tosyl-1,2,3-triazole (1a)[19] with steadily available tert-
butyl(cyclohexa-1,3-dien-1-yloxy)dimethylsilane (2a).[6a,20] After
several initial trials, we found that treatment of 1a (1 equiv) with
2a (3 equiv) in the presence of Rh2(OAc)4 in DCE at 110 oC
successfully delivered the desired silyl enol ether product 3a in
65% yield as a single diastereoisomer (Table 1, entry 1).
[a] Reaction conditions: 1a (0.2 mmol), 2a (0.4 mmol), Rh2(L)4 (2 mol%), DCE
(2 mL), 100 oC, under Ar, 2 h; then, CF3CO2H (0.1 mL), rt, 5 min. [b] Isolated
yields of 4a. [c] No reaction. [d] 5 mol% Rh2(oct)4 was used. [e] The reaction
was carried out in 4 mL DCE.
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With the optimized reaction conditions in hand, the generality
of the aza-[3+2] cycloaddition reaction was investigated in terms
of both triazoles 1 and silyl dienol ethers 2. As illustrated in
Scheme 3, the scope of triazoles was firstly investigated. Under
standard conditions, the reaction provided the hydroindolones 4
in moderate to good overall yields (53-84%) with tolerance of
various functionalities (4a-4q). Typically, substrates with
electron-donating substituents such as methoxyl and methyl
gave relatively higher yields compared to those with electron-
withdrawing groups (4a-4n). Moreover, bicyclic aryl substrates,
either 1-naphthyl or 2-naphthyl, also afforded the desired
hydroindolones in moderate yields (4o and 4p). It was
disappointing that no cyclized product could be observed when
4-butyl-1-tosyl-1,2,3-triazole was used under standard
conditions (4r).
Scheme 4. Scope of cyclic silyl dienol ethers 2.
Theoretically, when treatment with chiral rhodium(II) catalyst,
enantioselective formation of hydroindolones might be
accessible.[10d,10i] To this end, several chiral catalysts were
evaluated in the reaction of 1a with 2a under standard conditions
(Scheme 5).[22] The preliminary results showed that Rh2(S-
NTTL)4 and Rh2(S-PTTL)4 catalysts afforded 4a with 48% and
45% ee respectively (Scheme 5, entries 2, 3). In contrast, the
Rh2(S-TBSP)4 catalyst, with a proline derived ligand, failed to
show any enatioselectivity in this reaction (Scheme 5, entry 1).
Entry[a]
Rh2[L]4
Yield (%)[b]
ee (%)[c]
1
2
3
Rh2(S-TBSP)4
Rh2(S-NTTL)4
Rh2(S-PTTL)4
63
63
64
0
48
45
Scheme 5. Asymmetric [3+2] cycloaddition. [a] Reaction conditions: 1a (0.2
mmol) and 2a (0.4 mmol) were heated in DCE (2 mL) at 100 oC in the
presense of chiral Rh2(L)4 (2 mol%) for 2 h, then treated with TFA (0.1 mL)
and stirred at rt for 5 min. [b] Isolated yields of 4a. [c] Determined by chiral
HPLC analysis.
Scheme 3. Scope of 1-sulfonyl-1,2,3-triazoles 1.
Next, the scope of the reaction with respect to the silyl dienol
ether components 2 was examined. As summarized in scheme 4,
most of the substrates proceeded well to deliver single
diastereoisomer in moderate yields (4s-4y). This excellent
diastereoselectivity undoubtedly insures the dependable
formation of hydroindolone moiety in the late-stage synthesis.
Furthermore, both terminal alkenes and alkynes were tolerated
in these transformations (4t, 4v-4y). The structure and relative
configuration of 4t were confirmed by a single-crystal X-ray
analysis.
To demonstrate the utility of the denitrogenative aza-[3+2]
cycloaddition, Au(I)-catalyzed cyclizations of silyl enol ether 5
were then carried out (Scheme 6). After several attempts, we
found that Barriault’s conditions could give the optimal results.[23]
Typically, treatment of silyl enol ether 5a with 5 mol% of
o
Echavarren catalyst in toluene at 50 C for 17 hours gave the
predominant 6-endo-dig cyclization product 6a in excellent yield
and stereoselectivity. The structure of 6a was further confirmed
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by a single-crystal X-ray analysis. Analogously, cyclizations of
internal alkynes 5b and 5c also proceeded smoothly and
delivered the corresponding cyclized products 6b and 6c in
decent yields.
trans-stereoselectivity. It was worthy noted that the direct
reduction of 4q under classical conditions such as [NaBH3CN,
TFA] or [BF3•OEt2, Et3SiH] gave diastereoisomeric mixtures with
wrong configuration at C3 position. The relative configuration of
compound 10 was further confirmed by the X-ray
crystallographic analysis of its benzyl ether 11. Having
established all the requisite stereochemistries in the bicyclic
framework of 10, oxidation of the hydroxyl group and sequential
carbonyl group protection with glycol were then realized to
provide ketal 13 in good yield. Removal of tosyl group with
sodium naphthalide at -78 oC followed by Pictet-Spengler
cyclization with formalin afforded 5,11-methanomorphanthridin-
3-one 14 in 40% combined yield. The resulting compound 14
possessed a unique 5,11-methanomorphanthridine skeleton,
which was a basic ring system of montanine alkaloids.[24]
Scheme 6. Au(I)-catalyzed cyclizations of cyclic silyl enol ethers 5. Conditions:
Echavarren cataylst (5 mol%), PhMe (0.04 M), 50 oC, 17 h.
We then explored the synthetic feasibility of the Rh(II)-
catalyzed formal aza-[3+2] cycloaddition reaction (Scheme 7).
Compound 4a was initially selected as the substrate and treated
with phenylhydrazine hydrochloride in acetic acid to deliver the
corresponding bicyclic indole 7 with a complete regioselectivity
(Scheme 7, eq 1). Additionally, treatment of 4q with Pd/C under
a molecular hydrogen atmosphere led to cis-octahydroindolone
8 in excellent yield and stereoselectivity (Scheme 7, eq 2).
Scheme 8. Synthesis of 5,11-methanomorphanthridin-3-one 14. Conditions: a)
L-Selectride, THF, -78 oC, 1 h, 90%; b) NaBH3CN, TFA, DCM, rt, 1 h, 45%; c)
NaH, BnBr, TBAI, THF, 60 oC, 24 h, 50%; d) DMP, DCM, rt, 2 h, 78%; e)
glycol, TsOH, CH(OMe)3, PhH, reflux, 40 min, 90%; f) Na, naphthalene, DME,
-78 oC, 10 min; g) formalin, Et3N, MeOH, then HCl, 40% for 2 steps.
Scheme 7. Synthetic transfromations of the hydroindolones products.
Conditions: (1) PhNHNH2•HCl, AcOH, 90 oC, 3 h, 75%; (2) 10% Pd/C, H2 (2
atm), MeOH / EtOAc (v/v, 1:1), rt, 92%.
Conclusions
We have demonstrated a facile rhodium-catalyzed synthesis of
hydroindolones through denitrogenative formal [3+2] annulation
of 1-sulfonyl-1,2,3-triazoles with cyclic silyl dienol ethers. The
substrate scope is broad and a variety of functional groups can
be tolerated. Notably, the potential of this protocol has been
demonstrated by converting the representative products into the
bicyclo[3.3.1]alkenone framework and bicyclic indole compound
in high yields. Additionally, a stereoselective synthesis of 5,11-
methanomorphanthridine framework which extensively found in
montanine-type Amaryllidaceae alkaloids, has also been
achieved by using our developed methedology, that undoubtedly
To showcase the synthetic potential of the Rh(II)-catalyzed
formal aza-[3+2] cycloaddition reaction, a synthetic endeavor
toward 5,11-methanomorphanthridin-3-one, which shared the
key skeleton with montanine-type Amaryllidaceae alkaloids,[24]
had been successfully carried out. Firstly, as outlined in scheme
8, reduction of the cycloadduct 4q with L-Selectride in THF at -
78 C afforded alcohol 9 as a single product. The dihydropyrrol
moiety in compound 9 was then reduced with NaBH3CN to give
the trans-octahydroindolone 10 in moderate yield, with desired
o
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132.6, 131.8, 129.9, 128.7, 127.7, 127.2, 126.9, 125.7, 125.6, 121.1,
119.3, 117.4, 110.9, 109.1, 61.3, 43.5, 27.2, 23.3, 21.6. HRMS (ESI)
calcd for C27H25N2O2S [M+H]+: 441.1631, found 441.1640.
demonstrates its synthetic applicability in natural products total
syntheses.
Synthesis of cis-octahydroindolone compound 8: To a solution of
ketone 4q (28 mg, 0.07 mmol) in MeOH (2.5 mL) and ethyl acetate (2.5
mL) was added 10% palladium on carbon (3 mg). After being stirred
under 2 atm of hydrogen at rt for 3 h, the mixture was filtered through a
small plug of Celite and concentrated in vacuo. Purification by silica gel
chromatography afforded cis-octahydroindolone 8 (25 mg, 92%) as a
white solid, m.p. 196 – 198 oC; 1H NMR (400 MHz, CDCl3) δ 7.74 (d, J =
8.0 Hz, 2H), 7.35 (d, J = 8.0 Hz, 2H), 6.74 (d, J = 8.0 Hz, 1H), 6.62 (d, J =
1.6 Hz, 1H), 6.56 (d, J = 8.0 Hz, 1H), 5.94 (s, 2H), 4.00 (q, J = 6.4 Hz,
1H), 3.77 – 3.65 (m, 2H), 3.10 – 3.00 (m, 1H), 2.99 – 2.86 (m, 2H), 2.54 –
2.48 (m, 1H), 2.45 (s, 3H), 2.31 (dt, J = 17.6, 4.4 Hz, 1H), 2.16 – 2.01 (m,
1H), 1.67 – 1.58 (m, 1H), 1.57 – 1.46 (m, 1H). 13C NMR (100 MHz, CDCl3)
δ 210.0, 147.9, 146.6, 144.0, 133.9, 131.0, 129.9, 127.6, 120.6, 108.3,
108.1, 101.1, 59.2, 51.3, 45.4, 44.6, 42.6, 38.0, 21.6, 21.2. HRMS (ESI)
calcd for C22H24NO5S [M+H]+: 414.1370, found 414.1369.
Experimental Section
General methods and materials
Rhodium(II)-catalyzed cyclization reactions were carried out in a sealed
tube under argon. NMR spectra were recorded on Bruker 300 or 400
MHz spectrometers in CDCl3 or acetone d6. Chemical shifts were
reported as δ values relative to internal chloroform (δ 0.00 or 7.26 for 1H
NMR and 77.00 for 13C NMR) and acetone-d6 (δ 2.05 for 1H NMR and
206.26 for 13C NMR). High resolution mass spectra (HRMS) were
obtained on a 4G mass spectrometer by using electrospray ionization
(ESI) analyzed by quadrupole time-of-flight (QTof). All melting points
were measured with the samples after column chromatography (without
recrystallization). Column chromatography was performed on silica gel.
All reactions sensitive to air or moisture were carried out under argon in
dry and freshly distilled solvents, unless otherwise noted. Anhydrous THF,
toluene were distilled over sodium benzophenone ketyl under argon.
Anhydrous diisopropylamine was distilled over calcium hydride under
argon. Anhydrous DCE for the Rh(II)-catalyzed cyclization reactions was
used as commercially sourced chromatographically pure solvent and
dried over 4Å MS. All other solvents and reagents were used as obtained
from commercial sources without further purification. The analytical
HPLC was recorded on a HPLC machine equipped with Waters 1525
Binary HPLC Pump and Waters 2998 Photodiode Array Detector (Waters
HPLC machine). The chiral stationary phase was Daicel Chiralpak ID.
CCDC 1533606, 1533634, and 1555478 contain the supplementary
crystallographic data for this paper. These data are provided free of
charge by The Cambridge Crystallographic Data Centre.
Synthesis of alcohol compound 9: To a solution of ketone 4q (80 mg,
0,19 mmol) in dry THF (10 mL) was added a solution of L-Selectride in
THF (0.34 mL, 1.0 mol/L) at -78 oC. The reaction mixture was stirred for 1
h at the same temperature. Upon completion (monitored by TLC), the
mixture was quenched with NH4Cl (aq.), diluted with ethyl acetate (10
mL), extracted with ethyl acetate (10 mL). The combined organic layers
were washed with brine, dried over anhydrous Na2SO4. The residue was
concentrated in vacuo and purified by flash chromatography on silica to
afford the alcohol 9 (72 mg, 90%) as a white solid, m.p. 205 – 207 oC; 1H
NMR (400 MHz, CDCl3) δ 7.66 (d, J = 8.4 Hz, 2H), 7.32 (d, J = 8.0 Hz,
2H), 6.80 – 6.65 (m, 4H), 5.95 (s, 2H), 4.10 – 3.97 (m, 1H), 3.49 – 3.37
(m, 1H), 2.88 (dd, J = 13.6, 8.0 Hz, 1H), 2.63 (dt, J = 15.2, 4.8 Hz, 1H),
2.42 (s, 3H), 2.36 (d, J = 4.4 Hz, 1H), 1.93 (dt, J = 15.2, 4.4 Hz, 1H), 1.74
– 1.57 (m, 4H). 13C NMR (100 MHz, CDCl3) δ 148.0, 146.8, 144.2, 132.1,
129.8, 129.3, 127.7, 127.0, 124.9, 118.8, 108.4, 105.5, 101.1, 65.0, 60.4,
42.2, 32.7, 29.8, 21.7, 21.6. HRMS (ESI) calcd for C22H24NO5S [M+H]+:
414.1370, found 414.1360.
General procedure of Rh(II)-catalyzed cyclization: Under an argon
atmosphere, DCE (2 mL) was added to a reaction flask charged with
Rh2(oct)4 (3.1 mg, 2 mol%), 1-sulfonyl-1,2,3-triazoles 1 (0.2 mmol). Then
silyl dienol ether 2 (0.4 mmol) was added. The reaction was stirred at 100
oC for 2 h. After cooling to room temperature, trifluoroacetic acid (0.1 mL)
was added and stirred for additional 5 min. The resultant mixture was
concentrated and then purified by flash chromatography to give the
corresponding product 4.
Synthesis of compound 10: To a solution of compound 9 (420 mg, 1.01
mmol) in dry DCM (30 mL) was added NaBH3CN (77 mg, 1.22 mmol)
and trifluoroacetic acid (2 mL, 27 mmol) at room temperature. The
reaction mixture was stirred for 1 h. Upon completion (monitored by TLC),
the mixture was quenched with NaHCO3 (aq.) carefully, diluted with DCM.
The aqueous phase was extracted with DCM. The combined organic
layers were washed with brine, dried over anhydrous Na2SO4. The
residue was concentrated in vacuo and purified by flash chromatography
on silica to afford the compound 10 (189 mg, 45%) as a colorless foam.
1H NMR (400 MHz, CDCl3) δ 7.76 (d, J = 8.0 Hz, 2H), 7.36 (d, J = 8.0 Hz,
2H), 6.69 (d, J = 7.8 Hz, 1H), 6.46 (d, J = 8.0 Hz, 1H), 6.34 (s, 1H), 5.92
(s, 2H), 3.97 (dt, J = 12.8, 6.4 Hz, 1H), 3.82 – 3.72 (m, 1H), 3.63 – 3.51
(m, 1H), 3.33 – 3.19 (m, 1H), 3.13 (t, J = 10.0 Hz, 1H), 2.46 (s, 3H), 2.41
– 2.32 (m, 1H), 1.79 – 1.65 (m, 2H), 1.55 – 1.21 (m, 4H). 13C NMR (100
MHz, CDCl3) δ 147.9, 146.6, 143.5, 135.0, 132.4, 129.8, 127.3, 121.2,
108.3, 107.1, 101.0, 68.4, 59.4, 54.2, 44.4, 43.4, 39.9, 29.3, 21.5, 20.7.
HRMS (ESI) calcd for C22H23NO5S [M+H]+: 414.1526, found 414.1530.
General procedure of Au(I)-catalyzed cyclization: An oven-dried
round bottom flask (washed in a base bath prior to use) equipped with a
magnetic stirring bar, was charged with silyl enol ether 5, toluene (0.04
M), and the complex acetonitrile[(2-biphenyl)di-tert-butylphosphine] gold(I)
hexafluoroantimonate (Echavarren catalyst, 5 mol%). The mixture was
stirred for 17 h at 50 oC. After cooling to room temperature, the solvent
was evaporated off under reduced pressure and the residue was purified
by flash column chromatography on silica gel to give the cyclization
product 6.
Synthesis of indole compound 7: To a stirred solution of ketone 4a (44
mg, 0.12 mmol) in acetic acid (0.5 mL) was added phenylhydrazine
hydrochloride (22 mg, 0.15 mmol). The mixture was heated at 90 oC
under argon and stirred for 3 h, at which point the reaction mixture was
concentrated under reduced pressure. Purification by silica gel
chromatography afforded indol compound 7 as a reddish brown liquid (39
mg, 75%). 1H NMR (400 MHz, CDCl3) δ 7.98 (s, 1H), 7.68 (d, J = 7.6 Hz,
2H), 7.42 – 7.19 (m, 9H), 7.11 (t, J = 7.2 Hz, 1H), 7.03 (t, J = 8.0 Hz, 1H),
6.73 (s, 1H), 4.25 – 4.03 (m, 1H), 3.69 – 3.48 (m, 2H), 3.30 (dd, J = 16.8,
6.8 Hz, 1H), 3.07 (dd, J = 15.2, 7.2 Hz, 1H), 2.58 (dd, J = 14.8, 8.0 Hz,
1H), 2.41 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 144.2, 135.6, 133.0,
Synthesis of compound 11: To a stirred mixture of NaH (29 mg, 60%)
in dry THF (3 mL) was added the compound 10 (100 mg, 0.24 mmol).
After stirring for 20 min at room temperature, BnBr (72 μL, 0.6 mmol) and
TBAI (196 mg, 0.53 mmol) was added. The reaction mixture was stirred
for 24 h at 60 oC. After cooling to room temperature, the mixture was
quenched with water, extracted with ethyl acetate. The combined organic
layers were washed with brine, dried over anhydrous Na2SO4. The
residue was concentrated in vacuo and purified by flash chromatography
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10.1002/chem.201702893
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on silica to afford the compound 11 (61 mg, 50%) as a white crystal, m.p.
124 – 126 oC; 1H NMR (300 MHz, CDCl3) δ 7.76 (d, J = 8.1 Hz, 2H), 7.46
– 7.19 (m, 8H), 6.69 (d, J = 7.8 Hz, 1H), 6.46 (d, J = 9.6 Hz, 1H), 6.34 (s,
1H), 5.92 (s, 2H), 4.56 (q, J = 12.0 Hz, 2H), 4.07 – 3.88 (m, 1H), 3.81 –
3.67 (m, 1H), 3.43 – 3.21 (m, 2H), 3.13 (t, J = 9.9 Hz, 1H), 2.63 – 2.51 (m,
1H), 2.46 (s, 3H), 1.87 – 1.79 (m, 1H), 1.79 – 1.64 (m, 1H), 1.63 – 1.29
(m, 4H). 13C NMR (100 MHz, CDCl3) δ 148.0, 146.7, 143.4, 138.6, 135.3,
132.4, 129.8, 128.4, 127.5, 127.3 121.2, 108.3, 107.1, 101.0, 75.2, 67.0,
59.6, 54.2, 44.6, 43.8, 36.8, 26.6, 21.5, 20.8. HRMS (ESI) calcd for
C29H31NO5S [M+H]+: 506.1996, found 506.2000.
for additional 5 min. After washing with 5% NaOH (aq.), the mixture was
extracted with DCM, dried over Na2SO4. The residue was concentrated in
vacuo and purified by flash chromatography on silica to afford the
compound 14 (10 mg, 40% for 2 steps) as a colorless oil. 1H NMR (400
MHz, CDCl3) δ 6.51 (s, 1H), 6.45 (s, 1H), 5.88 (s, 2H), 4.31 (d, J = 17.2
Hz, 1H), 3.73 (d, J = 17.2 Hz, 1H), 3.31 (dt, J = 11.8, 7.2 Hz, 1H), 3.19
(dd, J = 11.8, 2.8 Hz, 1H), 3.02 (d, J = 11.8 Hz, 1H), 2.80 – 2.67 (m, 2H),
2.51 – 2.33 (m, 3H), 2.09 – 1.91 (m, 2H), 1.91 – 1.71 (m, 1H). 13C NMR
(100 MHz, CDCl3) δ 212.4, 146.4, 145.8, 136.1, 125.1, 106.8, 106.5,
100.7, 62.7, 60.1, 51.9, 50.5, 45.7, 44.1, 37.9, 24.4. HRMS (ESI) calcd
for C16H17NO3 [M+H]+: 272.1281, found 272.1282.
Synthesis of trans-octahydroindolone compound 12: To a solution of
compound 10 (81 mg, 0.20 mmol) in dry DCM (10 mL) was added DMP
(124 mg, 0.29 mmol) at room temperature. The reaction mixture was
stirred for 2 h at the same temperature. Upon completion (monitored by
TLC), the mixture was quenched with NaHCO3 (aq.), diluted with DCM.
The aqueous phase was extracted with DCM. The combined organic
layers were washed with brine, dried over anhydrous Na2SO4. The
residue was concentrated in vacuo and purified by flash chromatography
on silica to afford the compound 12 (63 mg, 78%) as a colorless foam. 1H
NMR (400 MHz, CDCl3) δ 7.73 (d, J = 8.4 Hz, 2H), 7.36 (d, J = 8.0 Hz,
2H), 6.72 (d, J = 8.0 Hz, 1H), 6.56 (dd, J = 8.0, 1.6 Hz, 1H), 6.50 (d, J =
1.6 Hz, 1H), 5.94 (s, 2H), 3.98 (td, J = 9.6, 6.0 Hz, 1H), 3.81 (dd, J = 9.2,
7.2 Hz, 1H), 3.21 (td, J = 11.2, 7.2 Hz, 1H), 3.08 – 2.90 (m, 2H), 2.68 (dd,
J = 15.6, 10.2 Hz, 1H), 2.47 (s, 3H), 2.41 – 2.31 (m, 1H), 2.28 – 2.16 (m,
1H), 2.16 – 2.05 (m, 1H), 1.93 – 1.50 (m, 1H), 1.73 – 1.62 (m, 1H). 13C
NMR (100 MHz, CDCl3) δ 209.5, 148.1, 147.0, 144.0, 133.4, 131.4,
129.9, 127.7, 121.0, 108.5, 107.1, 101.2, 58.1, 55.3, 47.4, 45.2, 43.7,
36.4, 22.7, 21.6. HRMS (ESI) calcd for C22H23NO5S [M+H]+: 414.1370,
found 414.1375.
Acknowledgements ((optional))
We thank the National Natural Science Foundation of China
(21572089, 21672017 and 21290183), the Shenzhen Science
and
Technology
Innovation
Committee
(JCYJ20150529153646078 and JSGG20160229150510483),
the Program for Changjiang Scholars and Innovative Research
Team in University (PCSIRT: IRT_15R28), the FRFCU (lzujbky-
2016-52 and lzujbky-2016-ct02) and the “111” Program of MOE
for financial support.
Keywords: rhodium-catalyzed • hydroindolone • Au(I)-catalyzed
• 5,11-methanomorphanthridin-3-one
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Synthesis of ketal compound 13: To a solution of compound 12 (40 mg,
0.10 mmol) in dry benzene (5 mL) was added ethylene glycol (11 μL,
0.10 mmol), pTSA (3.3 mg, 0.02 mmol) and CH(OMe)3 (11 μL, 0.20
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6.30 (d, J = 1.2 Hz, 1H), 5.91 (d, J = 1.2 Hz, 2H), 4.19 – 4.03 (m, 1H),
4.03 – 3.95 (m, 2H), 3.95 – 3.85 (m, 2H), 3.77 (dd, J = 9.6, 8.0 Hz, 1H),
3.32 – 3.14 (m, 1H), 3.06 (t, J = 10.0 Hz, 1H), 2.46 (s, 3H), 2.26 (ddd, J =
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121.2, 108.28, 108.22, 107.0, 101.0, 64.4, 64.2, 59.4, 54.4, 44.5, 43.1,
39.0, 29.2, 21.5, 20.1. HRMS (ESI) calcd for C24H27NO6S [M+H]+:
458.1632, found 458.1633.
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naphthalene (672 mg, 5.3 mmol) in dry DME (4 mL) was added sodium
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Chemistry - A European Journal
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Entry for the Table of Contents (Please choose one layout)
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Rhodium-catalyzed denitrogenative
[3+2] cycloaddition of 1-sulfonyl-1,2,3-
triazoles with cyclic silyl dienol ethers
to synthesize functionalized
Hongjian Yang, Shengtai Hou, Cheng
Tao, Zhao Liu, Chao Wang, Bin Cheng,
Yun Li,* Hongbin Zhai*
Page No. – Page No.
hydroindolones or their corresponding
silyl ethers has been developed.
Furthermore, the diastereoselective
synthesis of the framework of
montanine-type Amaryllidaceae
alkaloids has also been explored by
using this chemistry.
Rhodium-Catalyzed [3+2]
Denitrogenative Cycloaddition:
Access to Functionalized
Hydroindolones and the Framework
of Montanine-Type Amaryllidaceae
Alkaloids
Layout 2:
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Author(s), Corresponding Author(s)*
Page No. – Page No.
Title
Text for Table of Contents
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