Gold(i)-catalyzed intramolecular hydroamination and ring-opening of sulfonamide-substituted 2-(arylmethylene)cyclopropylcarbinols

Article abstract of DOI:10.1039/c2ob25512j

An interesting gold(i)-catalyzed intramolecular hydroamination and ring-opening of sulfonamide-substituted 2-(arylmethylene)cyclopropylcarbinols has been described in this context. A variety of 4-substituted isoxazolidine derivatives were obtained in good

Full text of DOI:10.1039/c2ob25512j

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PAPER
Gold(I)-catalyzed intramolecular hydroamination and ring-opening of
sulfonamide-substituted 2-(arylmethylene)cyclopropylcarbinols†
Di-Han Zhang, Kang Du and Min Shi*
Received 21st February 2012, Accepted 12th March 2012
DOI: 10.1039/c2ob25512j
An interesting gold(I)-catalyzed intramolecular hydroamination and ring-opening of sulfonamide-
substituted 2-(arylmethylene)cyclopropylcarbinols has been described in this context. Avariety of
4-substituted isoxazolidine derivatives were obtained in good to high yields through a highly
regioselective cleavage of a carbon–carbon single bond in the cyclopropane.
sulfonamide-substituted 2-(arylmethylene)cyclopropylcarbinols
1, which contain a coordinative double bond and a strained car-
Introduction
Homogeneous catalysis mediated by gold complexes has
received considerable attention in recent years,1 and the core of
these reactions rely on the interaction between gold catalysts and
π-bonds of alkenes, alkynes, and allenes. The most common
reaction pattern is the addition of nucleophiles to unsaturated
C–C bonds, initially activated by the gold complex acting as a
powerful soft catalyst, to efficiently construct new carbon–
carbon or carbon–heteroatom bonds.2–6 Methylenecyclopropanes
(MCPs) are generally used as building blocks in organic syn-
thesis for their accessibility as well as diverse reactivity driven
by the relief of ring strain. Over the past few decades, a series of
review articles have been published on the transformation of
these exo-methylene three-membered carbocycles.7 2-(Aryl-
methylene)cyclopropylcarbinols are another kind of MCP
bearing an additional hydroxymethyl group, and as demonstrated
by our group, can undergo a variety of transformations triggered
by the nucleophilic hydroxyl group under milder conditions.8
Several studies have focused on intramolecular nucleophilic
addition of MCPs bearing a nucleophilic group (Scheme 1). Our
group and Huang’s group reported the efficient stereoselective
synthesis of bicyclo[3.1.0]hexane from the reaction of 2-substi-
tuted MCPs with iodine (Mode A, Scheme 1).9 Lautens et al.
studied the MgI2-mediated ring expansions of secondary MCP
amides, which gave the isomeric five-membered unsaturated
lactams (Mode B, Scheme 1).10 Regioselective palladium-cata-
lyzed ring-opening cycloisomerization of MCP ketones has been
reported by Ma and co-workers (Mode C, Scheme 1).11 In view
bocycle and tether an additional nucleophilic sulfonamide group.
We envisioned that through an intramolecular hydroamination
along with a highly regioselective C–C bond cleavage (proximal
bond cleavage) of the cyclopropane in the presence of gold
complex, isoxazolidines 2 could be formed. Isoxazolidines,12
usually obtained by 1,3-dipolar cycloaddition of nitrones with
alkenes, are valuable intermediates for the synthesis of natural
products and possess very interesting biological properties.13
Results and discussion
Initial studies using sulfonamide-substituted 2-(arylmethylene)
cyclopropylcarbinol 1a [(E) configuration] as the substrate were
aimed at determining the reaction outcome and subsequently
optimizing the reaction conditions. The results are summarized
in Table 1. We found that an interesting 4-substituted
of this, we designed and synthesized
a novel type of
State Key Laboratory of Organometallic Chemistry, Shanghai Institute
of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling
Road, Shanghai 200032, P. R. China. E-mail: mshi@mail.sioc.ac.cn
†Electronic supplementary information (ESI) available: Experimental
procedures, characterization data of new compounds. CCDC reference
number 816966. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c2ob25512j
Scheme 1 Intramolecular nucleophilic addition of 2-substituted MCPs.
Nu = nucleophile, E = electrophile.
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Table 1 Optimization of reaction conditions for gold(I)-catalyzed
intermolecular hydroamination and ring-opening
Table 2 Substrate scope of the gold(I)-catalyzed intermolecular
hydroamination and ring-opening of sulfonamide-substituted 2-
methylenecyclopropylcarbinols 1
Yield (%)b
2a
Yield (%)b
2
Entrya
Catalyst (x mol%)
Entrya
1
R1
R2
R3
1
2
3
4
5
6
7
8
[(Ph3P)AuCl]/AgOTf (5)
[(Ph3P)AuCl]/AgOTf (10)
[(Me3P)AuCl]/AgOTf (10)
[(tBu3P)AuCl]/AgOTf (10)
[(lPr)AuCl]/AgOTf (10)
[(tBuXPhos)Au(NCMe)]SbF6 (10)
AgOTf (10)
[(Ph3P)AuCl] (10)
HOTf (2)
[(Ph3P)AuCl]/AgOTf (10)
59
95
78
20
32
24
81
NRc
18
93
1c
2
3
4
5
6
7
8
9
1b
1c
1d
1e
1f
1g
1h
1i
C6H5
H
H
H
H
H
H
H
H
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Bs
Ns
Bs
Ns
Ts
2c, 79
2b, 86
2d, 83
2e, 78
2f, 67
2g, 50
2h, 69
2i, 64
2j, 67
2i, 79
2j, 84
Complex
4-ClC6H4
4-FC6H4
4-MeC6H4
4-MeOC6H4
3,4-Cl2C6H3
2,4-Cl2C6H3
4-BrC6H4
4-BrC6H4
H
9
1j
1k
1l
H
10d
10
11
12
4-BrC6H4
4-BrC6H4
H
a [1a] = 0.05 M. b Isolated yield. c NR = no reaction. d 2,4,6-Tri-tert-
butylpyrimidine (10 mol%) was added.
H
1m
C6H5CH2CH2
a All reactions were carried out using 1 (0.2 mmol) in the presence of
[(Ph3P)AuCl]/AgOTf (10 mol%) in DCE (2.0 mL) at 80 °C for 24 h.
b Isolated yield. c In the presence of [(Ph3P)AuCl]/AgSbF6 (10 mol%).
Ts
= 4-toluenesulfonyl; Ns = 4-nitrobenzenesulfonyl; Bs = 4-
isoxazolidine derivative 2a [(E) configuration] was formed in
59% yield using [(Ph3P)AuCl]/AgOTf (5 mol%) as the catalyst
in 1,2-dichloroethane (DCE) at 80 °C (Table 1, entry 1). The
structure of compound 2a was confirmed by NMR spectroscopic
data and X-ray diffraction (see ESI†). Adding [(Ph3P)AuCl]/
AgOTf (10 mol%) afforded 2a in 95% yield (Table 1, entry 2).
Using [(Me3P)AuCl], [(tBu3P)AuCl] or [(IPr)AuCl] as a gold
complex gave 2a in 78%, 20% and 32% yields, respectively
(Table 1, entries 3–5). In the presence of [(tBuXPhos)Au-
(NCMe)]SbF6, 2a could be also obtained in 24% yield (Table 1,
entry 6). Control experiments indicated that using AgOTf alone
as the catalyst gave 2a in 81% yield and using [(Ph3P)AuCl]
alone as the catalyst did not promote the reaction (Table 1,
entries 7 and 8). Moreover, in the presence of HOTf (2 mol%),
2a could be formed in 18% yield as well (Table 1, entry 9). The
addition of 2,4,6-tri-tert-butylpyrimidine (10 mol%, a proton
scavenger) into the reaction system to exclude trace of HOTf
gave 2a in 93% yield (Table 1, entry 10). Therefore, the optimal
reaction conditions have been identified to carry out the reaction
in DCE at 80 °C using [(Ph3P)AuCl]/AgOTf as the catalyst. Car-
rying out the reactions in other solvents, silver salts and different
amounts of HOTf did not improve the reaction outcomes (see
Table S1 in ESI†).
We next examined the substrate generality of this reaction
under optimized conditions and the results are shown in Table 2.
As can be seen from Table 2, for substrates 1b–1h (R3 = Ts) the
reactions proceeded smoothly to furnish the desired products
2b–2h in good yields, regardless of whether they have electron-
rich, electron-poor, or electron-neutral aromatic rings at their
alkene moieties (Table 2, entries 1–7). Changing the sulfonamide
substitution R3 to Bs and Ns produced the corresponding isoxa-
zolidine derivative 2i and 2j in 64% and 67% yields, respectively
(Table 2, entries 8 and 9). Further examination of substrate
(Z)-1k and (Z)-1l revealed that the expected five-membered
heterocycles 2i and 2j were formed in 79% and 84% yields,
respectively (Table 2, entries 10 and 11). Only in the case of
bromobenzenesulfonyl.
Scheme 2 Isotopic labeling experiments.
aliphatic MCP alcohol 1m (R1 = C6H5CH2CH2), complex
product mixtures were formed under the standard conditions
(Table 2, entry 12). The product structures of 2b–2j were deter-
mined by NMR spectroscopic analysis, mass spectroscopy (MS),
and HRMS (see ESI†). 2-(Arylmethylene)cyclopropyltosylamide
3a (a simple tosyl amide without the oxygen atom) is inactive in
this gold-catalyzed hydroamination (see ESI†).
To elucidate the cyclization mechanism, deuterium labeling
experiment was performed as shown in Scheme 2. Carrying out
the reaction of 2-(arylmethylene)cyclopropylcarbinol 1a in D2O
(3 equiv.) led to the corresponding product [D]-2a in 55% yield
along with 32% deuterium incorporation at its olefinic carbon
atom.
A plausible mechanism for this reaction is outlined in
Scheme 3 on the basis of the above deuterium labeling experi-
ment.14 Cationic Au(I) complex A (or Lewis acid) first coordi-
nates to the alkene moiety of 1 [(E) or (Z) configuration] to give
intermediate B, which then produces a carbocationic intermedi-
ate C. There might be an equilibrium between the intermediate
C and intermediate C′, in which intermediate C is the preferred
active species based on the formation of (E)-isoxazolidine pro-
ducts. The intermediate C undergoes a common intramolecular
hydroamination along with the ring-opening of cyclopropane15
3764 | Org. Biomol. Chem., 2012, 10, 3763–3766
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dissolved in 1,2-dichloroethane (DCE) (2.0 mL) in an Schlenk
tube, and (Ph3P)AuCl/AgOTf (10 mol%) were added. Then, the
reaction mixture was stirred at 80 °C until the reaction com-
pleted. The solvent was removed under reduced pressure and the
residue was purified by a flash column chromatography (SiO2) to
give the corresponding products 2 in moderate to excellent
yields.
Compound 1a. A white solid. Mp: 113–115 °C. IR (CH2Cl2)
ν 3242, 2930, 1597, 1486, 1395, 1163, 1007, 817, 718 cm−1
.
1H NMR (CDCl3, 300 MHz, TMS) δ 1.30–1.35 (m, 1H, CH2),
1.66–1.68 (m, 1H, CH2), 1.83–1.92 (m, 1H, CH), 2.45 (s, 3H,
CH3), 3.86 (dd, J = 10.8 Hz, J = 7.8 Hz, 1H, CH2), 4.02 (dd, J =
10.8 Hz, J = 6.3 Hz, 1H, CH2), 6.72 (d, J = 1.2 Hz, 1H, CH),
7.14 (s, 1H, NH), 7.35 (d, J = 8.7 Hz, 4H, Ar), 7.44 (d, J = 8.7
Hz, 2H, Ar), 7.83 (d, J = 8.7 Hz, 2H, Ar). 13C NMR (CDCl3,
75 MHz, TMS) δ 9.9, 11.8, 21.7, 79.3, 118.7, 120.9, 125.8,
128.2, 128.6, 129.7, 131.5, 133.4, 136.3, 144.9. MS (ESI) m/z
408 (M+ + H). HRMS (ESI) Calcd for C18H19NO3SBr
(M+ + H): 408.0264, Found: 408.0261.
Scheme 3 A plausible reaction mechanism. L = ligand. LA = Lewis
acid.
Acknowledgements
to give the corresponding five-membered heterocyclic intermedi-
ate D. The hydrolysis of intermediate D produces 4-substituted
isoxazolidine derivative 2 and regenerates the Au(I) complex A
to complete the catalytic cycle.
We thank the Shanghai Municipal Committee of Science and
Technology (11JC1402600), National Basic Research Program
of China (973)-2010CB833302, and the National Natural
Science Foundation of China for financial support (21072206,
20472096, 20872162, 20672127, 20732008 and 21121062).
Conclusions
In summary, we have developed a novel gold(I)-catalyzed cycli-
zation reaction to construct five-membered N,O-heterocyclic pro-
Notes and references
ducts
from
sulfonamide-substituted
2-(arylmethylene)
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mechanistic investigation are under way in our laboratory.
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General remarks
1H and 13C NMR spectra were recorded at 400 (or 300) and 100
(or 75) MHz, respectively. Mass and HRMS spectra were
recorded by ESI or EI method. The employed solvents were dry
up by standard methods when necessary. Commercially obtained
reagents were used without further purification. All reactions
were monitored by TLC with silica gel coated plates. Flash
column chromatography was carried out using 300–400 mesh
silica gel at increased pressure.
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hydroamination and ring-opening of sulfonamide-substituted 2-
(arylmethylene)cyclopropylcarbinols under the standard
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