Gold versus silver-catalyzed intermolecular hydroaminations of alkenes and dienes

Article abstract of DOI:10.1002/adsc.201100478

Comparative studies about the hydroamination of unactivated alkenes and dienes catalyzed by either cationic gold(I) triphenyl phosphite complexes or silver salts were performed using sulfonamides, anilines and carbamates as nucleophiles. Gold-catalyzed reactions generally, need lower loadings than those carried out with silver salts. Simple alkenes react only with sulfonamides and weak aromatic amines such as p-nitroaniline, whereas for conjugated dienes carbamates can also be used. Carbon-carbon double bond isomerization is observed only with gold similarly to when triflic acid was used, affording mixtures of regioisomeric products in the same cases. Silver-catalyzed hydroaminations failed with terminal alkenes, except with styrenes. Conjugate dienes can be hydroaminated either at 85 °C in toluene or at room temperature in dichloromethane. Non-conjugated 1,4- and 1,5-dienes suffer double hydroamination leading to saturated N-tosylated heterocyclic amines The catalytic cycle for the silver(I)-catalyzed hydroamination process has been computationally analyzed, resembling gold(I)-catalyzed processes, although with some significant differences. Copyright

Full text of DOI:10.1002/adsc.201100478

FULL PAPERS
DOI: 10.1002/adsc.201100478
Gold versus Silver-Catalyzed Intermolecular Hydroaminations of
Alkenes and Dienes
Xavier Giner,a Carmen Nꢀjera,a,* Gꢀbor Kovꢀcs,b Agustꢁ Lledꢂs,b
and Gregori Ujaqueb,*
a
Dpto. Quꢁmica Orgꢀnica and Instituto de Sꢁntesis Orgꢀnica, Universidad de Alicante, Apdo 99, E-03080 Alicante, Spain
Fax : (+34)-96-590-3549; e-mail: cnajera@ua.es
Departament de Quꢁmica, Universitat Autꢃnoma de Barcelona, E-08193 Bellaterra, Spain
b
E-mail: gregori@klingon.uab.es
Received: June 17, 2011; Revised: August 25, 2011; Published online: December 13, 2011
Dedicated to Prof. Avelino Corma on the occasion of his 60th birthday
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adcs.201100478.
Abstract: Comparative studies about the hydroami- with terminal alkenes, except with styrenes. Conju-
nation of unactivated alkenes and dienes catalyzed gate dienes can be hydroaminated either at 858C in
by either cationic gold(I) triphenyl phosphite com- toluene or at room temperature in dichloromethane.
plexes or silver salts were performed using sulfon- Non-conjugated 1,4- and 1,5-dienes suffer double hy-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ings than those carried out with silver salts. Simple ver(I)-catalyzed hydroamination process has been
alkenes react only with sulfonamides and weak aro- computationally analyzed, resembling gold(I)-cata-
matic amines such as p-nitroaniline, whereas for con- lyzed processes, although with some significant dif-
jugated dienes carbamates can also be used. Carbon- ferences.
carbon double bond isomerization is observed only
with gold similarly to when triflic acid was used, af-
fording mixtures of regioisomeric products in the Keywords: alkenes; dienes; gold(I) complexes; silver
same cases. Silver-catalyzed hydroaminations failed salts; sulfonamides
Introduction
have been used for the intermolecular hydroamina-
tion of olefins and conjugated dienes. Iodine[8] and N-
The catalyzed hydroamination (HA) of alkenes, al- bromosuccinimide[9] have been recently employed for
lenes, dienes and alkynes is a fundamental transfor- the addition of sulfonamides[8,9] and carbamates[9] to
mation for the synthesis of acyclic and heterocyclic vinylarenes. The acid-catalyzed addition of nitrogen-
amines, enamines and imines.[1] Over the last two de- ated compounds to alkenes needs an adequate acid-
cades several Brønsted and Lewis acids have shown base compatibility for successful reactions; sulfona-
catalytic activity in atom-economical inter- and intra- mides, carboxamides, carbamates and anilines are the
molecular hydroaminations of unsaturated systems. In most common nucleophilic reagents. Similar consider-
spite of this great effort, several aspects should still be ations can be made when metal salts or complexes
improved, especially in intermolecular catalyzed HA are used as catalysts. Bi
processes, such as its suitability for different unacti- 1,3-dienes,[10] Cu
(OTf)2/dppe for styrenes, norbornene
vated alkenes, as well as the isomerization and dime- and cyclohexa-1,3-diene,[11] FeCl3 for styrenes,[12]
rization of these substrates and the catalyst efficiency. InBr3,[13] Zr(OTf)4,[14] and Pt(II) complexes activated
ACHTUGTNRNENUG(OTf)3/[CuACHTUNTGNERN(UGN CH3CN)4]PF6 for
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
[15]
Several Brønsted acids, such as triflic acid,[2] by AgBF4 for acyclic and cyclic alkenes have also
PhNH3BACHTUNGTRENNUNG
(C6F5)4,[3] proton-exchange montmorillonite,[4] been used in HA reactions. Other homogeneous cata-
silicotungstic acid,[5] phosphomolybdic acid supported lysts, such as alkali metal amides,[16] lanthanides,[17]
on silica gel[6] and SO3H-functionalized ionic liquids[7] and early (Ti, Zr) transition metals[18] work mainly
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Xavier Giner et al.
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with amines forming metal-amide and metal-imide in- dienes, along with a DFT-based study focused on the
termediates in the last case. Late transition metals elucidation of the reaction mechanism.
(Ru, Rh, Pd, Ni, Ir, Au) catalyzed the HA of alkenes
mainly with nitrogenated nucleophiles of low basicity,
such as anilines, carboxamides and sulfonamides by a Results and Discussion
[19]
À
C C activation mechanism.
Notable progress has been achieved in this decade Catalyst Screening
using gold-catalyzed processes.[20] Among them inter-
molecular HA reactions of unactivated alkenes and The hydroamination of norbornene (1a) with p-tolu-
1,3-dienes have been performed with electrophilic
ACHTUNGTRENeNUNG nesulfonamide (2a), in anhydrous toluene under
gold(I) complexes using sulfonamides and carbamates argon using MW heating, was chosen as a model reac-
as nucleophiles.[21,22] Recently, we have communicated tion for catalyst screening (Table 1). Gold(I) chloride
that (triphenyl phosphite)gold(I) chloride/AgOTf[23] is without and with triphenylphosphine as ligand com-
a more efficient catalyst than the same combination bined with silver triflate or tetrafluoroborate gave
with triphenylphosphine. Performing control experi- high yields >90% using 5 mol% loading (Table 1, en-
ments we found that AgOTf also catalyzed this inter- tries 1–4). The reaction time could be decreased from
molecular HA reaction.[24] In this full paper we com- 30 to 15 min when triphenylphosphine was used as
pare the scope and activities of Au(I) and Ag(I) as ligand. When the loadings of the last two complexes
catalysts[25] in the intermolecular HA of alkenes and were reduced to 0.1 mol%, compound 3aa was ob-
Table 1. Catalysts screening for the addition of TsNH2 to norbornene.[a]
Entry
Catalyst [mol%]
Temperature [8C]
Time [min]
Yield [%][b]
1
2
3
4
5
6
7
8
AuCl/AgOTf (5)
AuCl/AgBF4 (5)
A
ACHTUNGTRENNUNG
N
N
R
E
N
90
85
85
85
90
85
85
85
85
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
85
30
15
15
15
30
15
15
15
15
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
96
90
99 (92)
99
58
1
99
80
99
99
98 (73)
99
94 (90)
82
60
99
22
99
78
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26[c]
N
ACHTUNGTRENNUNG
G
N
G
E
T
N
G
75
10
4
5
99
99 (98)
75
N
U
[d]
N
–
[a]
Reactions were performed with TsNH2 (171 mg, 1 mmol), norbornene (376 mg, 4 mmol), catalyst (see column) in dry tol-
uene (2 mL) under argon in a microwave reactor (70 W, 10 psi) with air stream cooling.
Determined by GC, based on TsNH2. In parenthesis isolated yield after flash chromatography.
Reaction was performed with conventional heating in air without light protection.
14 h.
[b]
[c]
[d]
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Gold versus Silver-Catalyzed Intermolecular Hydroaminations of Alkenes and Dienes
Table 2. Hydroamination of norbornene and 1,3-cyclohexadiene with different nucleophiles.[a]
Entry
Catalyst
[mol%]
RNH2
Solvent
Product No.
Yield [%][b]
1[c]
2[c]
3[c]
4
5
6
7
8
9
Au (0.05)
Ag (1)
Au (0.1)
Ag (5)
Au (5)
Au (5)
Ag (5)
Au (5)
Ag (5)
Au (0.1)
Ag (5)
Au (1)
Ag (1)
Ag (5)
Au (5)
Ag (5)
Au (5)
Ag (1)
Au (5)
Ag (5)
Au (5)
Ag (5)
TsNH2 (2a)
TsNH2 (2a)
4-MeO-C6H4SO2NH2 (2b)
4-MeO-C6H4SO2NH2 (2b)
4-NO2-C6H4SO2NH2 (2c)
MeSO2NH2 (2d)
PhMe
PhMe
PhMe
PhMe
PhMe
dioxane
dioxane
PhMe
PhMe
PhMe
PhMe
dioxane
dioxane
PhMe
CH2Cl2
dioxane
PhMe
PhMe
3aa
3aa
3ab
3ab
3ac
3ad
3ad
3ag
3ag
5aa
5aa
5ab
5ab
5ab
5ad
5ad
5ae
5ae
5af
94 (90)
98 (73)
99 (96[d])
32
0
(65)
57
88 (81)
0
66
86
77 (60)
0
MeSO2NH2 (2d)
p-NO2-C6H4NH2 (2g)
p-NO2-C6H4NH2 (2g)
TsNH2 (2a)
10[e]
11
12
13
14
15[f]
16
17
18
19[g]
20[g]
21
22
TsNH2 (2a)
4-MeO-C6H4SO2NH2 (2b)
4-MeO-C6H4SO2NH2 (2b)
4-MeO-C6H4SO2NH2 (2b)
MeSO2NH2 (2d)
MeSO2NH2 (2d)
saccharin (2e)
saccharin (2e)
CBzNH2 (2f)
CBzNH2 (2f)
p-NO2-C6H4NH2 (2g)
p-NO2-C6H4NH2 (2g)
60
(75)
(47)
0
45 (27)
98 (65)
99 (96)
56 (52)
25
ACHTUNGTRENNUNG
G
5af
5ag
5ag
PhMe
PhMe
[a]
Reactions were performed with amide (1 mmol), alkene or diene (4 mmol), catalyst (see column) in dry solvent (2 mL)
under Ar in a microwave reactor (70 W, 10 psi) at 908C for 30 min with air stream cooling.
Determined by GC, based on RNH2. In parenthesis isolated yield after flash chromatography.
1.2 equiv. of norbornene (1a) were used.
After recrystallization from hexane/EtOAc.
1.2 equiv. of cyclohexa-1,3-diene (4a) were used.
[b]
[c]
[d]
[e]
[f]
Reaction performed at room temperature during 24 h.
Under conventional thermal conditions at 508C during 23 h.
[g]
tained in only 58% and 1% yields, respectively, The same gold complex without a silver salt gave neg-
(Table 1, entries 5 and 6). When the more electron- ligible yields. Silver triflate gave 98% yield using the
withdrawing ligand trisACHTNURGTNEUNG[3,5-bis(trifluoromethyl)phe- same conditions as with [(PhO)3P]AuCl/AgOTf
nyl]phosphine[26] was used for the preparation of the (Table 1, compare entries 10 and 11). The loading of
LAuCl complex and AgOTf or AgBF4 as silver salts, the gold catalyst formed by [(PhO)3P]AuCl/AgOTf
99% and a lower 80% yield were obtained, respec- could be decreased to 0.1 and 0.05 mol% providing
tively (Table 1, entries 7 and 8). A less expensive 3aa in high yields. However, with only 0.01 mol%
strong p-acceptor phosphorus ligand such as triphenyl loading the yield dropped down to 60% (Table 1, en-
phosphite was used for gold(I) chloride[27] and tries 12, 13, and 15). These results indicate that tri-
AgOTf[26] as silver salt. In this case quantitative yields phenyl phosphite was a more efficient ligand than the
of 3aa with 5 mol% and even with 1 mol% loadings phosphines (Table 1, compare entry 5 with 12 and 13).
were obtained, although with the reaction time in- Silver triflate provided a lower (82%) yield compared
creasing from 15 to 30 min (Table 1, entries 9 and 10). to when the gold complex was used, both in
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Xavier Giner et al.
FULL PAPERS
0.05 mol% loading (Table 1, compare entries 13 and as solvent due to solubility problems. Again, the gold
14). complex showed better catalytic performance than
The use of 1 mol% of silver perchlorate either com- the silver salt, affording product 3ad in 65% yield
bined with [(PhO)3P]AuCl or alone, gave 99% and (Table 2, entries 6 and 7). A weak basic amine such as
22% of 3aa, respectively (Table 1, entries 16 and 17). p-nitroaniline (2g) could be used only for the gold-
The loadings of the phosphite ligand and AgClO4 catalyzed HA of 1a providing 3ag in 81% yield using
were decreased to 0.5, 0.1, 0.05 and 0.01 mol% giving a 5 mol% catalyst loading (Table 2, entries 8 and 9).
product 3aa in quantitative yield only in the first case In general, gold-catalyzed HA needed a lower cata-
(Table 1, entries 18–21). From these results it can be lyst loading than the silver counterparts but only in
concluded that AgOTf is a more efficient salt than the case of norbornene.
AgClO4 for this transformation. On the other hand,
Cyclohexa-1,3-diene (4a) was used as a representa-
AgBF4 failed with or without the gold(I) complex tive conjugate diene for the HA reaction with differ-
(Table 1, entries 22 and 23). However, AgSbF6 ent sulfonamides, carbamates and p-nitroaniline as
showed a good efficiency using 1 mol% loading nucleophiles working under microwave heating at
(Table 1, entries 24 and 25). Under conventional heat- 908C during 30 min (Table 2, entries 10–22). In the
ing the best reaction (Table 1, entry 13) needed 14 h case of p-toluenesulfonamide (2a), 0.1 mol% of Au
giving a lower 75% yield (Table 1, entry 26).
catalyst and 5 mol% of AgOTf were used affording
product 5aa in 66% and 86% yields, respectively
(Table 2, entries 10 and 11).
Nucleophile Screening
Similar experiments were carried out with p-
methoxybenzenesulfonACTHNUTRGNEaNUG mide (2b) and methanesulfo-
When different amides such as sulfonamides and car- namide (2d) as nucleophiles in dioxane or dichloro-
bamates were allowed to react with norbornene (1a) methane affording products 5ab and 5ad, respectively,
in the presence of [(PhO)3P]AuCl/AgOTf or simple in moderate yields (Table 2, entries 12–16). The reac-
AgOTf as catalysts, only electron-rich sulfonamides tion of 4a with p-methoxybenzenesulfonamide (2b)
were appropriate nucleophiles for this HA (Table 2, catalyzed by AgOTf failed in dioxane and was carried
entries 1–7). The HA with p-toluenesulfonamide (2a) out in toluene (Table 2, entry 14). The HA with sac-
worked with both Au and Ag catalysts, but a higher charin (2e) only took place with 1 mol% of AgOTf
loading must be used in the latter case (Table 2, en- giving 5ae in a modest 27% yield (Table 2, entries 17
tries 1 and 2). However, the addition of p-methoxy- and 18). Benzyl carbamate (2f) could be added to cy-
benzenesulfonamide (2b) only took place efficiently clohexadiene (4a) using either Au or Ag as catalysts,
when using 0.1 mol% of the gold complex (Table 2, but under conventional heating at 508C for ca. 1 d in
entries 3 and 4), whereas in the case of p-nitroben- 1,2-dichloroethane as solvent, yielding 65% or 96% of
ACHTUNGTRENNUNGzenesulfonamide (2c), the Au-catalyzed HA failed product 5af, respectively (Table 2, entries 19 and 20).
(Table 2, entry 5). For the HA with methanesulfona- In the case of p-nitroaniline compound 5ag was ob-
mide (2d), the catalyst loading should be increased to tained in 52% yield using the gold catalyst, compared
5 mol% and dioxane instead of toluene must be used to a modest 25% yield when using Ag, in both cases
Table 3. Hydroamination of alkenes with TsNH2 catalyzed by either by [(PhO)3P]AuCl/AgOTf or AgOTf and by TfOH.[a]
Entry Alkene
No. Solvent Catalyst
(mol%)
Temperature
[8C]
Time
Product
No. Yield
[%][b]
N
1
2
3
4
5
6
7
8
1a
PhMe
PhMe
PhMe
PhMe
PhMe
CH2Cl2 Au (5)
CH2Cl2 Ag (5)
CH2Cl2 TfOH (1)
PhMe
PhMe
PhMe
neat
Au (0.05)
Ag (0.5)
Au (0.05)
Ag (1)
85
85
90
90
14 h
4 h
3aa (99)
96[c] (99)
30 min[d]
30 min[d]
30 min[d]
24 h
90[c] (94)
73 (98)
8
TfOH (0.1) 90
25
25
25
85
85
85
90
90
85
85
3
24 h
24 h
24 h
14 h
(99)
91[2c]
9
1b
Au (2)
Ag (2)
TfOH (1)
Au (5)
Ag (5)
Au (2)
Ag (2)
3ba 64 (84)
38 (50)
58[2c]
10
11
12
13
14
15
22 h
30 min[d]
30 min[d]
14 h
(35)
neat
neat
neat
71 (88)
84 (95)
(21)
14 h
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Gold versus Silver-Catalyzed Intermolecular Hydroaminations of Alkenes and Dienes
Table 3. (Continued)
Entry Alkene
No. Solvent Catalyst
(mol%)
Temperature
[8C]
Time
Product
No. Yield
[%][b]
N
16
17
1c
PhMe
PhMe
Au (1)
Ag (4)
85
85
24 h
14 h
3ca 75 (98)
(4)
18
19
1d
PhMe
PhMe
Au (1)
Ag (1)
90
90
30 min[d]
30 min[d]
3da 90 (98)
25 (53)
20
21
22
1e
1f
1g
neat
neat
neat
Au (5)
Ag (5)
TfOH (1)
85
85
85
14 h
14 h
14 h
3ea 70 (98)
79 (98)
(66)
23
24
25
neat
neat
neat
Au (5)
Ag (5)
TfOH (1)
85
85
85
14 h
14 h
14 h
3ea 60 (98)
(0)
(57)
26
27
28
29
30
PhMe
PhMe
PhMe
PhMe
PhMe
Au (5)
Ag (5)
TfOH (5)
Au (5)
Ag (5)
85
85
85
90
90
14 h
14 h
3ga (61)
(72)
14 h
70[2c]
30 min[d]
30 min[d]
66 (78)
58 (76)
68
31
1h
1i
PhMe
Au (5)
85
24 h
3ha
(80)[e]
32
33
PhMe
PhMe
Ag (5)
Au (5)
85
90
24 h
(0)
30 min[d]
(59)[f]
65
34
PhMe
Au (5)
85
24 h
3ia
(99)[g]
35
36
PhMe
PhMe
Ag (5)
Au (5)
85
90
24 h
0
30 min[d]
91
(95)[g]
(0)
37
38
PhMe
PhMe
Ag (5)
TfOH (5)
90
90
30 min[d]
30 min[d]
75
(97)[h]
39
40
1j
PhMe
PhMe
Au (5)
Ag (5)
85
85
14 h
14 h
3ja
73 (78)[i]
0
41
42
43
44
45
46
PhMe
PhMe
PhMe
PhMe
neat
Au (5)
Ag (5)
Au (5)
Ag (5)
Au (5)
Ag (5)
90
90
85
85
85
85
30 min[d]
30 min[d]
14 h
14 h
14 h
34
0
1k
3ka 26 (27)
1
91 (98)[j]
0
neat
14 h
[a]
Reactions were performed with TsNH2 (171 mg, 1 mmol), alkene (4 mmol), catalyst (see column) in dry solvent (2 mL) or
under solvent-free conditions under conventional or MW heating and argon atmosphere.
Isolated yield after flash chromatography. In parenthesis isolated crude yield determined by GC based on TsNH2.
Isolated yield after recrystallization.
Under microwave heating (70 W, 10 psi) with air stream cooling.
19% of N-tosyl-1-phenyl-1-propanamine was also obtained.
45% of N-tosyl-1-phenyl-1-propanamine was also obtained.
9% of N-tosyl-1-(p-methoxyphenyl)-1-propanamine was also obtained.
25% of N-tosyl-1-(p-methoxyphenyl)-1-propanamine was also obtained.
2.2% of N-tosyl-1-phenyl-2-butanamine and 0.4% of N-tosyl-1-phenyl-1-butanamine were also obtained.
33% of N-tosyl-3-octanamine and 22% of N-tosyl-4-octanamine were also obtained.
[b]
[c]
[d]
[e]
[f]
[g]
[h]
[i]
[j]
with a 5 mol% loading (Table 2, entries 21 and 22). In of cyclohexa-1,3-diene showed similar efficiency, gold
general, the conjugate diene 4a showed higher reac- only failing when saccharin was used as nucleophile.
tivity than norbornene with a wider scope concerning
nucleophiles. Gold- and silver-catalyzed HA reactions
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Xavier Giner et al.
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Au- vs. Ag-Catalyzed Hydroamination of Alkenes
ing isobornyl cation. In order to explain the racemiza-
tion process, this isobornyl cation should suffer a met-
The scope of the gold versus silver-catalyzed HA of allotropy if the metal is in an endo-position. Final
different cyclic and acyclic alkenes was studied with attack of the p-toluenesulfonamide to the less hin-
p-toluenesulfonamide (2a) under conventional or mi- dered exo-position followed by protonolysis provided
crowave heating (Table 3). Several experiments were racemic 3ea and regeneration of the catalyst
also carried out to make comparisons with TfOH-cat- (Scheme 1). In the case of 1f, after the coordination
alyzed hydroaminations either previously described or to the cationic gold complex, subsequent rearrange-
performed by us under the same conditions. In the ment would result in the formation of two isobornyl
case of norbornene (1a) the HA took place in >94% cations by prototropy which, after subsequent nucleo-
yield either in the presence of the gold complex philic exo-attack by the p-toluenesulfonamide and
(0.05 mol%) or silver salt (0.5–1 mol%), both at 858C protonolysis, would give rise to racemic 3ea. In gener-
under conventional heating and under microwave ir- al, cyclic alkenes can be hydroaminated by both gold
radiation at 908C (Table 3, entries 1–4). However, and silver catalysts, except for exocyclic alkenes such
TfOH gave only 8% of 3aa under MW heating as b-pinene, which did not react when AgOTf was
(Table 3, entry 5). Hydroaminations at room tempera- used as catalyst.
ture took place only using 5 mol% of AgOTf or
Styrene (1g) gave product 3ga in moderate yields
1 mol% of TfOH,[2c] affording 3aa in quantitative either under conventional or MW heating with both
yields, whereas Au failed under these reaction condi- gold and silver catalysts and TfOH[2b] in toluene
tions (Table 3, compare entries 6–8).
(Table 3, entries 26–30). However, the homologous al-
For the HA of cyclohexene (1b) in toluene, 2 mol% lylbenzene (1h) reacted with p-toluenesulfonamide
of gold or silver catalysts were used under heating at only under gold catalysis (Table 3, entries 31–33).
858C achieving 64% or 38% yield, respectively, of
Compound 3ha was mainly obtained together with
product 3ba (Table 3, entries 9 and 10), whereas a its regioisomer N-tosyl-1-phenyl-1-propanamine in a
58% yield was obtained when using 1 mol% of TfOH 4/1 ratio when heating to 858C, (Table 3, entry 31).
as catalyst (Table 3, entry 11).[2c] Under solvent-free Similarly, p-methoxyallylbenzene (1i) gave product
conditions, silver was a better catalyst than gold 3ia and its regioisomer N-tosyl-1-(p-methoxyphenyl)-
under MW heating, whereas gold was better than 1-propanamine in a ca. 10/1 and 4/1 ratio, respectively,
silver under conventional heating (Table 3, entries 12– only under gold or TfOH catalysis (Table 3, en-
15). The highest yield (84%) for compound 3ba was tries 34, 36, and 38). However, AgOTf was inefficient
obtained by conventional heating under solvent-free under both conditions (Table 3, entries 35 and 37). 4-
conditions using the gold complex (2 mol%) as cata- Phenylbut-1-ene (1j) was efficiently hydroaminated in
lyst (Table 3, entry 14).
Cyclooctene (1c) showed a lower reactivity than cy- provide compound 3ja together with small amounts
clohexene and could be hydroaminated with p-tolu- of N-tosyl-1-phenylbut-2-amine and -1-amine
enesulfonamide using 1 mol% of the gold catalyst (Table 3, entry 39). Nevertheless, when MW heating
toluene at 858C using 5 mol% of the gold complex to
ACHTUNGTRENNUNG
(Table 3, entry 16). 1,4-Dihydro-1,4-methanonaphtha- was used, very poor results were obtained (Table 3,
lene (1d)[29] was also hydroaminated at 858C under entry 41), again the silver-catalyzed reactions failed
MW heating to afford product 3da in higher 90% (Table 3, entries 40 and 42). For other terminal acyclic
yield using 1 mol% of gold, whereas only a 25% yield alkenes, such as oct-1-ene (1k), the HA took place in
was obtained in the case of the silver salt (Table 3, en- high yield only under solvent-free conditions using
tries 18 and 19).
the gold complex as catalyst (Table 3, entries 43–46).
(+)-a-Pinene (1e) and (À)-b-pinene (1f) afforded In this case, product 3ka was obtained together with
the same racemic N-tosylisobornylamine (3ea)[30] regioisomeric sulfonamides at the 3- and 4-positions
using the cationic gold complex (5 mol%) as catalyst, of the aliphatic skeleton, in 2/1.5/1 ratio.
but only under solvent-free conditions and heating at
It can be concluded that in the case of monosubsti-
858C (Table 3, entries 20 and 23). However, AgOTf tuted olefins only styrenes were reactive in both Au
was an efficient catalyst only in the case of 1e, the and Ag catalysis, whereas AgOTf gave very poor cat-
HA failing in the case of 1f (Table 3, entries 21 and alytic activity with the alkyl-substituted ones. This dif-
24). Under the same neat conditions and in the pres- ferent behaviour between Au and Ag is probably due
ence of 1 mol% of TfOH, 3ea was obtained in 66% to the fact that terminal alkenes are less prone to
and 57% yield, respectively, although accompanied by suffer HA due to competitive C=C isomerization in
secondary products derived from 1e and 1f (Table 3, acid-catalyzed reactions.
entries 22 and 25). It can be proposed that 1e after
When 0.5 mL of 4-phenyl-but-1-ene (1j) was al-
the coordination to Au or Ag at the endo-face gave lowed to react with the gold complex (0.05 mmol) or
rise to a tertiary carbocation that suffeed a typical with AgOTf (0.05 mmol) overnight at 858C, only the
1,2-Wagner–Meerwein shift to afford the correspond- former produced isomerization of the C=C double
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Gold versus Silver-Catalyzed Intermolecular Hydroaminations of Alkenes and Dienes
Scheme 1. Postulated mechanisms for the formation of compound 3ea.
bond giving a 3/1 mixture of 4-phenylbut-1-ene and 4- tries 1, 2 and 4). However, when AgOTf was used as
phenylbut-2-ene. In addition to the inability of catalyst under the latter conditions 5 mol% was nec-
AgOTf to isomerize alkenes, we have observed much essary to provide 5aa in good yield (Table 2, entry 5).
cleaner reactions with Ag than with Au, because only In the case of using TfOH, 5aa was obtained in 63%
gold afforded alkene dimerization by-products. The yield using 1 mol% loading at 508C (Table 4,
reason why only Au promotes the double bond migra- entry 3).[2c] Working under room temperature condi-
tion is still unclear and further investigation is tions, the use of 1 mol% of gold complex in dichloro-
needed. It can be proposed that, after coordination of methane as solvent afforded 5aa in 90% yield
cationic Au or Ag with the C=C double bond, gold (Table 4, entries 6 and 7). As mentioned above, cyclo-
forms better covalent sigma bonds with the C atom cta-1,3-diene (4b) gave moderate yields of product
than silver[31] generating the corresponding vicinal car- 5ba only under heating at 858C and in toluene as sol-
benium cation. Alternatively, TfOH can be employed vent (Table 4, entries 8–12). Acyclic dienes, such as
as catalyst giving similar results to those with the Au penta-1,3-diene (4c) and 3-methylpenta-1,3-diene
complex but affording more secondary by-products.
(4d), were successfully hydroaminated under the
three sets of reaction conditions (Table 4, entries 13–
28). In addition, diene 4c was used as a Z/E: 1/1.8 dia-
stereomeric mixture and afforded product 5ca mainly
as the E-diastereomer (Table 4, entries 13–18), espe-
Au- vs. Ag-Catalyzed Hydroaminations of Dienes
Hydroamination of dienes was also performed with p- cially under room temperature conditions (Table 4,
toluenesulfonamide as nucleophile (Table 4). Conju- entries 17 and 18). Working under room temperature
gated 1,3-dienes showed a higher reactivity than al- conditions, TfOH provided 5ca in similar yield
kenes using both catalysts either under heating or at (Table 4, entry 19). Moreover, similar results were ob-
room temperature, except for cycloocta-1,3-diene (4b) served in the case of 3-methylpenta-1,3-diene (4d)
(Table 4, entries 1–28). Cyclohexa-1,3-diene (4a) was that is available commercially as a Z/E: 1/2.5 diaste-
hydroaminated in toluene under conventional and reomeric mixture (Table 4, entries 20–28). Further-
MW heating using low catalyst loadings (Table 2, en- more, the corresponding hydroamination with p-tol-
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Xavier Giner et al.
Table 4. Hydroamination of dienes with TsNH2 catalyzed by either by [(PhO)3P]AuCl/AgOTf or AgOTf and by TfOH.[a]
FULL PAPERS
Entry Diene
No. Solvent Cat.alyst
(mol%)
Temperature
[8C]
Time
Product
No. Yield
[%][b]
Z/E
Ratio[c]
1
2
3
4
5
6
7
8
4a PhMe Au (0.1)
PhMe Ag (0.1)
PhMe TfOH (1)
PhMe Au (0.1)
PhMe Ag (5)
CH2Cl2 Au (1)
CH2Cl2 Ag (1)
4b PhMe Au (1)
PhMe Ag (1)
85
85
50
90
90
25
25
85
85
85
85
85
85
85
90
90
25
25
25
85
85
14 h
14 h
25 h
5aa (68)
76 (87)
63[2c]
20 min[d]
30 min[d]
24 h
(66)
(86)
90 (99)
49 (58)
5ba 51 (64)
52 (66)
58[2c]
(14)
(9)
5ca (85)
73 (88)
85 (97)
(52)
65 (99)
(66)
55 (77)
5da 77 (98)
73 (88)
24 h
14 h
14 h
22 h
14 h
14 h
14 h
14 h
9
10
11
12
13
14
15
16
17
18
19
20
21
PhMe TfOH (1)
neat
neat
Au (1)
Ag (1)
4c[e] PhMe Au (0.1)
PhMe Ag (0.1)
PhMe Au (0.1)
PhMe Ag (0.1)
CH2Cl2 Au (1)
1/5
1/4.3
1/7
1/11
1/16
1/26
1/8
30 min[d]
30 min[d]
24 h
24 h
24 h
14 h
14 h
CH2Cl2 Ag (1)
CH2Cl2 TfOH (1)
4d[f] PhMe Au (0.1)
PhMe Ag (0.1)
1/6
1/8
22
23
24
25
26
27
28
29
30
PhMe TfOH (0.1)
PhMe Au (0.1)
PhMe Ag (0.1)
PhMe TfOH (0.1)
CH2Cl2 Au (1)
85
90
90
90
25
25
25
85
85
24 h
(21)
85 (97)
(90)
(51)
86 (99)
(66)
1/49
1/6
30 min[d]
30 min[d]
30 min[d]
24 h
1/11
1/21
1/49
1/49
1/49
CH2Cl2 Ag (1)
CH2Cl2 TfOH (1)
24 h
24 h
14 h
14 h
59 (93)
6a 83 (79)[g]
(27)[h]
4e neat
Au (5)
Ag (5)
neat
31
32
33
34
35
36
37
38
39
40
41
42
4f PhMe Au (5)
85
85
85
85
90
90
90
85
85
85
85
85
14 h
14 h
14 h
14 h
6a (47)
44 (56)[i]
(3)
(23)
7a 70 (96)
0
neat
neat
neat
neat
neat
neat
neat
neat
Au (5)
Ag(5)
TfOH (5)
Au (2)
Ag (2)
TfOH (1)
Au (2)
TfOH (1)
Au (5)
4j
30 min[d]
30 min[d]
30 min[d]
14 h
(94)
(98)
(98)
14 h
14 h
14 h
14 h
4k neat
neat
8a 44 (61)
54 (85)
(70)
Ag (5)
neat
TfOH (1)
[a]
Reactions were performed with TsNH2 (171 mg, 1 mmol), diene (4 mmol), catalyst (see column) in dry solvent (2 mL) or
under solvent-free conditions under conventional or MW heating and argon atmosphere.
[b]
[c]
[d]
[e]
[f]
Isolated yield after flash chromatography. In parenthesis isolated crude yield determined by GC based on TsNH2.
1
Determined by H NMR over the crude product.
Under microwave heating (70 W, 10 psi) with air stream cooling.
Z/E: 1/1.8.
Z/E: 1/2.5.
cis/trans: 1/2.75.
cis/trans: 1.5/1.
cis/trans: 1/2.2.
[g]
[h]
[i]
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Gold versus Silver-Catalyzed Intermolecular Hydroaminations of Alkenes and Dienes
uenesulfonamide afforded product 5da mainly or ex-
clusively as the E diastereomer, Au and Ag giving
similar results under the three sets of reaction condi-
tions. However, TfOH afforded lower yields than the
Au- or Ag-catalyzed processes (Table 4, entries 22, 25,
and 28).
In the case of the non-conjugated hexa-1,4-diene
(4e), the reaction must be heated under solvent-free
conditions affording a 1/2.75 mixture of cis/trans-2,5-
dimethylpyrrolidine (6a) in good yield when the gold
complex was used as catalyst (Table 4, entries 29 and
30). The same product 6a was obtained starting from
hexa-1,5-diene (4f) but in lower yield, the reaction
taking place only under gold catalysis at 858C either
in toluene or under solvent-free conditions (Table 4,
entries 31 and 32). However, silver failed in this case
and TfOH gave a low yield of product 6a (Table 4,
entries 33 and 34).
Figure 1. X-ray structure of compound 7d.
5-Vinylnorborn-2-ene (4j) gave tricyclic heterocycle
7a only under gold catalysis and neat conditions
either by conventional or MW heating (Table 4, en-
tries 35 and 38), the reaction failing when using
AgOTf as catalyst (Table 4, entry 36). The same prod-
uct 7a was obtained in the presence of 1 mol% of
triflic acid either under MW or conventional thermal
conditions in 94% and 98% crude yields, respectively
(Table 4, entries 37 and 39). The structure of this hy-
droamination product was determined by X-ray dif-
fraction analysis of the methanesulfonamide deriva-
tive 7d,[32] which was obtained in 70% yield by heating
at 858C, under the same reaction conditions
(Figure 1).
Compounds 7 could be formed by successive iso-
merization of 4j through cationic intermediates A–C
(Scheme 2). After the attack of the sulfonamide on
intermediate C, the first hydroamination product D
could be formed, which suffers anti-Markonikov in-
tramolecular hydroamination to provide product 7.
Scheme 2. Postulated mechanism for the formation of com-
pound 7.
Finally, when 5-methylenebicycloACTHNUTRGNEUNG[2.2.1]hept-2-ene
(4k) was allowed to react with p-toluenesulfonamide
(1a), the tricyclic product 8a was obtained in moder-
ate yield under solvent-free conditions or convention-
al heating at 858C either under gold or silver catalysis
in 44% and 54% yields, respectively (Table 4, en-
tries 40 and 41). In addition, compound 8a was ob-
tained in 70% crude yield by using 1 mol% of TfOH
at 858C during 14 h (Table 4, entry 42). For the struc-
ture assessment of tricyclic compound 8a, the corre-
sponding crystalline methanesulfonamide derivative
8d was prepared in 74% yield using 5 mol% AgOTf
as catalyst under heating at 858C for 14 h, and was
submitted to X-ray diffraction analysis (Figure 2).[33]
This type of structure 8 has been previously de-
scribed in the Ritter reaction of 5-methylenebicyclo-
Figure 2. X-ray structure of compound 8d.
ACHTUNGTRENNUNG[2.2.1]hept-2-ene (4k) with acetonitrile giving the cor- cies to the methylene moiety affording intermediate
responding acetamide.[34] Its formation can be ex- A which, after intramolecular cyclization, leads to in-
plained by binding of the cationic gold or silver spe- termediate B. After the final addition of the sulfon-
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Xavier Giner et al.
FULL PAPERS
anism revealed that when a tautomerization process
takes place on the added nucleophile the energy bar-
rier for the overall proton transfer process is much
lower. The tautomerization takes place on the nucleo-
phile (a carbamate in the studied case) once it is
added to the double bond. The energy barrier for the
tautomerization process alone was found to be quite
high. Nevertheless, the presence of triflate anion was
shown to dramatically decrease the energy barrier for
this step. Subsequent proton transfer from the tauto-
mer to the C atom generates the final product. Substi-
tution of the product by a new reactant alkene closes
the catalytic cycle. The hydroamination reaction cata-
lyzed by TfOH has been also computationally ana-
lyzed.[22b] The reaction mechanism was shown to be
rather similar with the H+ activating the double bond,
but with the nucleophilic attack and the proton trans-
fer taking place concertedly. Such a study on a model
olefin also showed that the energy barrier for the
TfOH-catalyzed reaction was somewhat higher than
that for the Au(I)-catalyzed process.
Scheme 3. Postulated mechanism for the formation of com-
pound 8.
Experimental attempts to isolated the cationic
[(PhO)3P]AuOTf complex failed. However, from
31P NMR spectra could be stablished that the signal
from the covalent complex [(PhO)3P]AuCl at d=
109.93 ppm was moved to 95.11 when AgOTf was
added. The formation of [(PhO)3P]Au
(m/z=548) was better detected by ESI-MS in reaction
+A
CHTUNGRTEN(NUNG CH3CN)
AHCTUNGTRENNUNG
of [(PhO)3P]AuCl with AgOTf in acetonitrile.[23] The
weak interaction between [(PhO)3P]Au+ and the tri-
flate anion would facilitate the coordination of the
C=C double bond to the metal center. The coordina-
tion of the vinyl (CH=CH2) group of diene 4d to
[(PhO)3P]Au+ was observed by 13C NMR.[23] This co-
ordination took place mainly with the E-diastereomer
Scheme 4. Catalytic cycle for the Au(I)-catalyzed hydroami-
nation.
ACHTUNGTRENNUNGamide and proton transfer regenerating the catalyst, because the corresponding signal from the diene ap-
product 8 is formed (Scheme 3).
pears at lower fields.[23]
The reaction mechanism for the Ag(I)-catalyzed
hydroamination of dienes has been analyzed by
means of DFT calculations. The computational analy-
sis was initially performed taking the AgOTf mole-
Au vs. Ag Hydroamination Reaction Mechanism
Theoretical analysis is a valuable tool for understand- cule as the active catalyst, 3-methylpenta-1,3-diene as
ing reaction mechanisms as shown, for instance, in a model substrate and methanesulfonamide as a nu-
other Au-catalyzed reactions.[35] The reaction mecha- cleophile. The initial step analyzed corresponds to a
nism for the PR3Au(I)-catalyzed hydroamination has 3-methylpenta-1,3-diene coordination to the AgOTf
been computationally studied by some of us.[22] The catalyst giving rise to a linear species. The next step
main reaction steps for this process in the case of eth- should involve the nucleophilic addition of the sulfo-
ylene (see Scheme 4) can be summarized as follows: namide to the coordinated diene. Nevertheless, the
(i) substitution of the counterion by the alkene at the product of this nucleophilic attack could not be locat-
coordination sphere of the gold center, giving rise to ed on the potential energy surface. All geometry opti-
À
the catalytically active species; (ii) nucleophilic attack mizations starting from a structure with the N C
of the amide on the coordinated alkene forming an bond already formed, spontaneously lead to the rup-
Au-alkyl species; (iii) proton transfer from the nucleo- ture of this bond and the regeneration of the separat-
phile to the newly formed alkyl ligand. The last one is ed reactants. These results suggest that a neutral
the most striking step within the overall catalytic AgOTf molecule is not a catalytic species, since nucle-
cycle. The direct proton transfer was found to be en- ophilic addition does not take place. Besides AgOTf,
ACTHNUTRGNEUNG
ergetically prohibitive. A deeper analysis of the mech- other cationic species as Ag+, [Ag(diene)]+ and
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Gold versus Silver-Catalyzed Intermolecular Hydroaminations of Alkenes and Dienes
Figure 3. Reaction energy profile for the Ag(I)-catalyzed hydroamination of dienes (energies in kcalmolÀ1).
[Ag
could, in principle, be active catalysts for the process. 8.2 kcalmolÀ1. The last step involves the proton trans-
The complex [Ag
(diene)2]+ is by far the most stable fer from the base to the C atom coordinated to metal
ACHTUNGTRENNUNG
(diene)2]+ can also be present in solution and mide. The relative energy barrier for this step is
AHCTUNGTRENNUNG
species among the cationic Ag(I) species present in center. The relative energy barrier for the last step is
solution; Ag-diene bond dissociation energy in 14.2 kcalmolÀ1, therefore becoming the rate-determin-
[AgACHTUNGTRENNUNG
(diene)2]+ is 21.1 kcalmolÀ1. In addition, diene ing step for this reaction. The overall energy barrier
concentration in the reaction media is high enough to for the reaction is 26.3 kcalmolÀ1. The formation of
displace the equilibrium position to the formation of the final product coordinated to metal center is exo-
[AgACHTUNGTRENNUNG
(diene)2]+ species. According to this, the latter thermic by 29.5 kcalmolÀ1. Calculations suggest that
species was selected for the theoretical analysis of the in solution the reaction takes place in three steps: nu-
reaction mechanism, even though the mechanism cleophilic addition and two proton transfer steps
should be quite similar for all cationic species.
using the nucleophile as a proton shuttle. The transi-
The presence of counterions or Lewis bases in the tion states are depicted in the Figure 4, respectively.
reaction media can play a significant role in proton
For the case of Au(I)-catalyzed HA process it was
transfer processes.[36] In order to evaluate the effects found that the nucleophile (carbamate) performs a
of the base on the proton transfer process, an addi- tautomerization during the reaction. The analogous
tional base molecule (sulfonamide) was explicitly in- mechanism was evaluated for the case of sulfonamide
corporated into the calculations. The reaction energy acting as the nucleophile and an Ag(I) species as the
profile for this process is shown in Figure 3.
catalyst. As previously described, the initial step cor-
The initial step (once the diene binds to the metal responds to the nucleophilic addition. Then, the tau-
center) corresponds to the nucleophilic attack of the tomerization process might take place on the bonded
sulfonamide on the coordinated diene. The energy nucleophile. The direct tautomerization process is too
barrier for this process is 9.1 kcalmolÀ1 whereas the energy demanding to be a feasible step within the re-
formed intermediate lies 7.1 kcalmolÀ1 over the reac- action mechanism, having a global energy barrier of
tants. The reaction must involve a proton transfer 63.0 kcalmolÀ1. Alternatively, as in the case of the
from the sulfonamide to the C atom directly bonded gold system, the tautomerization process may be cata-
to the metal atom. The direct proton transfer is too lyzed by the presence of a base. Thus, a second mole-
energy demanding, with an energy barrier of 49.6 kcal cule of the base (sulfonamide) was explicitly included
molÀ1. A proton-transfer agent has to participate in in the theoretical calculations. In this case the tauto-
the reaction, and the sulfonamide represents by far merization takes place in one step in solution, the sul-
the best candidate in solution for this purpose.
fonamide acting as a proton shuttle. The overall
Hence, a proton transfer process including an addi- energy barrier in this case is 28.0 kcalmolÀ1. The
tional sulfonamide was investigated.[36] Calculations global energy barrier in this reaction mechanism is
show that the proton transfer takes place in two steps. somewhat higher in energy than the previous one,
In the first one the proton goes to the second sulfona- which suggests that the most favourable reaction
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FULL PAPERS
Figure 4. Geometries of the transitions states: TS1 nucleophilic addition, TS2 proton transfer to the base, and TS3 proton
transfer to C atom, respectively (distances in ꢅ).
mechanism involves a proton-transfer catalyzed by
the presence of the base without including tautomeri-
zation.[38] This behaviour is different from that found
for the Au(I) catalyst using a system with a carbamate
as a nucleophile.
The energy difference[22] between the tautomeric in-
termediates in the case of Au(I)-carbamate system
was 1.6 kcalmolÀ1, nearly isoenergetic, whereas for
the case of Ag(I)-sulfonamide the energy difference
between the tautomeric structures is 16.5 kcalmolÀ1.
The origin of these differences can be related on one
hand to the nature of the nucleophile. Thus, the
energy difference between the tautomers in their iso-
lated structures[22] is 12.7 kcalmolÀ1 for carbamate
and 12.2 kcalmolÀ1 for sulfonamide, respectively;
therefore, tautomerization of the isolated molecules
has similar energetic requirements. The nature of the
metal center is playing an important role for stabiliz-
ing the tautomeric intermediates and they go in oppo-
site directions: Au(I) is able to stabilize the less stable
tautomer by 14.3[22] kcalmolÀ1, whereas Ag(I) desta-
bilizes the less stable tautomer by 4.3 kcalmolÀ1.
Thus, the nature of the metal center is also affecting
the relative energies of the intermediates in both re-
action mechanisms.
According to the results obtained, the proposed
catalytic cycle for the Ag(I)-catalyzed hydroamination
is shown in Scheme 5. The catalytic cycle can be di-
vided into the following steps: formation of the Ag(I)
cationic species, N-nucleophilic addition and a step-
Scheme 5. Catalytic cycle for the Ag(I)-catalyzed hydroami-
nation.
wise proton transfer giving rise to the final product
and regenerating the catalyst. Alternatively, the
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Gold versus Silver-Catalyzed Intermolecular Hydroaminations of Alkenes and Dienes
thane)=8.93]. All energies given in the text correspond to
proton transfer may go through the tautomeric inter-
mediate, although this process is more energetically
demanding.
those including the effect of the bulk solvent, which were
obtained by adding the contribution of the Gibbs energy of
solvation to the gas phase total energies with the larger
basis set.
In the case of the transition states, normal coordinate
analysis has been used to calculate the imaginary frequen-
cies, and for each transition structure we calculated the in-
trinsic reaction coordinate (IRC) routes towards the corre-
sponding minima. If the IRC calculations failed to reach the
energy minima on the potential energy surface, we per-
formed geometry optimizations from the final phase of the
IRC path.
Conclusions
It has been found that [(PhO)3P]AuCl/AgOTf or just
AgOTf afforded good catalytic efficiency in the hy-
droamination of alkenes with sulfonamides and p-ni-
troaniline. The gold catalyst showed a wider scope
than the silver salt, which was unable to catalyze the
hydroamination of terminal alkenes. The hydroamina-
tion of conjugate dienes can be performed with
Hydroamination of Alkenes and Dienes; General
Procedure
sulfonACHTUNGTRENNUNGamides, p-nitroaniline, and carbamates as nucle-
ophiles, either in gold- or silver-catalyzed reactions. In
the case of non-conjugated 1,4- or 1,5-dienes the To a mixture of gold complex and or silver salt (see Table 1,
Table 2, Table 3, and Table 4) and nitrogenated nucleophile
(1 mmol) in dry solvent (2 mL, see Table 1, Table 2, Table 3,
and Table 4) was added the alkene or 1,3-diene (4 mmol)
with magnetic stirring in a sealed tube under argon atmos-
phere in the dark. For neat experiments (Table 3 and
Table 4) no solvent was added. After the corresponding re-
action time under the conditions indicated in Table 1,
Table 2, Table 3, and Table 4 (for microwave heating the
vessel was sealed with a pressure lock and the mixture was
heated at 908C in a CEM Discover MW reactor at 70 W,
inter- and intramolecular hydroaminations gave the
saturated heterocyclic compounds. Regarding the re-
action mechanism, gold- and silver-catalyzed hydroa-
mination processes have related reaction mechanisms
albeit including significant differences. The initial step
corresponds to the formation of a cationic species by
substituting the counterion with the diene, which is
followed by the nucleophilic addition step. Then, two
successive proton transfer steps assisted by a second
nuclephile molecule give rise to the final product and 10 psi with air stream cooling during 30 min), the reaction
mixture was cooled at room temperature and water (2 mL)
and brine (2 drops) were added. The organic layer was sepa-
rated and the aqueous phase was extracted with ethyl ace-
tate (2ꢆ10 mL). All organic phases were mixed, dried with
MgSO4 and evaporated. Pure products were obtained by re-
crystallization or by flash chromatography.
regenerate the catalytic species. In the case of the
gold-catalyzed reaction the last step was found to
follow a tautomerization process (using carbamate as
nucleophile) and the presence of TfOÀ was found to
be crucial for assisting such a process. Nevertheless,
for the case of the silver-catalyzed reaction using sul-
fonamide as a nucleophile, the tautomerization pro-
cess, even if it is energetically accessible, it is not re-
quired. The proton transfer using the nucleophile as a
4-Methyl-N-(1,7,7-trimethylbicycloACTHNUTRGNEU[GN 2.2.1]heptan-2-yl)ben-
zenesulfonamide (3ea): White solid; mp 2098C (CH2Cl2); Rf
0.47 (hexane/ethyl acetate: 4/1); IR (KBr): n=3276, 2956,
1323, 1158, 1095, 1024, 923, 814, 706, 681 cmÀ1 1H NMR
;
proton shuttle is found to be the most favourable pro- (300 MHz, CDCl3): d=0.77 (s, 3H), 0.78 (s, 3H), 0.86 (s,
3H), 0.96–1.05 (m, 2H), 1.45–1.70 (m, 5H), 2.43 (s, 3H),
3.11 (td, J=8.2, 5.71 Hz, 1H), 4.46 (d, J=8.7 Hz, 1H), 7.29
(d, J=8.1 Hz, 2H), 7.74 (d, J=8.3 Hz, 2H); 13C NMR
(75 MHz, CDCl3): d=12.1, 20.1, 20.3, 21.5, 26.8, 36.3, 40.0,
44.9, 47.0, 48.5, 61.2, 127.1, 129.6, 138.1, 143.1; MS (EI): m/z
(%)=307 (4) [M+], 155 (31), 153 (11), 152 (100), 136 (13),
135 (50), 133 (19), 121 (20), 109 (30), 108 (11), 107 (20), 106
(12), 95 (52), 93 (35), 92 (12), 91 (86), 79 (18), 77 (13), 69
(10), 67 (18), 65 (25); HR-MS: m/z=307.1644, calcd. for
C17H25NO2S [M]+: 307.1606.
cess.
Experimental Section
Computational Methods
The model selected for calculation was AgOTf as catalyst,
CH3SO2NH2 as nucleophile and 3-methylpenta-1,3-diene as
the diene. The geometry optimizations have been carried by
DFT calculations with the program package Gaussian09[39]
and the B3LYP[40] combination of functionals. The SDD[41]
pseudo-potential was employed for the silver centre, and the
standard 6-31G(d) basis set was used for the other atoms.
Energies have been obtained by means of single point calcu-
lations at the M06 level using the same SDD pseudo-poten-
tial, including a series of f-functions for the metal center and
1-Tosyloctahydro-3a,6-methanoindole (7a): Yellow oil; Rf
0.40 (hexane/ethyl acetate: 4/1); IR (KBr): n=2956, 2868,
1342, 1305, 1163, 1095, 1042, 821, 658 cmÀ1
;
1H NMR
(400 MHz, CDCl3): d=1.08–1.11 (m, 2H), 1.40–1.53 (m,
2H), 1.58–1.62 (m, 3H), 1.73–1.80 (m, 1H), 1.83 (dd, J=9.3,
3.4 Hz, 1H), 1.98–2.11 (m, 1H), 2.30 (s, 1H), 2.43 (s, 3H),
2.97 (dd, J=9.3, 4.4, 1H), 3.42 (td, J=13.8, 2.4 Hz, 1H),
3.59 (td, J=14.1, 9.2 Hz, 1H), 7.32 (d, J=11.1 Hz, 2H), 7.70
(d, J=11.0 Hz, 2H); 13C NMR (100 MHz, CDCl3): d=21.5,
27.4, 28.3, 30.0, 38.1, 39.8, 41.4, 49.9, 56.4, 67.9, 127.5, 129.5,
134.5, 143.1; MS (EI): m/z (%)=291 (100) [M+], 290 (36),
263 (61), 250 (42), 249 (13), 237 (18), 236 (98), 155 (41), 136
the extended 6-311GACTHNUTRGNE(NUG d,p) basis set for the other atoms. The
effect of the bulk solvent (dichloromethane) was estimated
by the application of the polarizable continuum model
(PCM)[42] as implemented in Gaussian 09 [e(dichlorome-
Adv. Synth. Catal. 2011, 353, 3451 – 3466
ꢄ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
3463

Xavier Giner et al.
FULL PAPERS
(91), 109 (13), 108 (20), 95 (21), 92 (12), 91 (96), 81 (36), 80
(15), 79 (23), 67 (28); HR-MS m/z=291.1283, calcd. for
C16H21NO2S [M]+: 291.1293.
fonamide (5aa),[45] N-(cyclohex-2-enyl)-4-methoxybenzene-
sulfonamide (5ab),[10] 2-(cyclohex-2-en-1-yl)benzo[d]isothia-
zol-3(2H)-one 1,1-dioxide (5ae),[46] benzyl cyclohex-2-en-1-
ylcarbamate (5af),[47] N-(cyclohex-2-en-1-yl)-4-nitroaniline
(5ag),[48] N-(cyclohex-2-enyl)methanesulfonamide (5ad),[49]
(Z)-N-(cyclooct-2-en-1-yl)-4-methylbenzenesulfonamide
1-(Methylsulfonyl)octahydro-3a,6-methanoindole
(7d):
White solid; mp 1158C (hexane/CH2Cl2); Rf 0.14 (hexane/
ethyl acetate: 4/1); IR (KBr): n=2958, 2865, 1450, 1369,
1332, 1239, 1139, 1050, 972, 779, 762 cmÀ1
;
1H NMR
(5ba),[50]
(E)-4-methyl-N-(pent-3-en-2-yl)benzenesulfon-
(400 MHz, CDCl3): d=1.15 (d, J=12.6 Hz, 1H), 1.25–1.30
(m, 2H), 1.57–1.61 (m, 1H), 1.62–1.69 (m, 2H), 1.75–1.93
(m, 4H), 2.33 (s, 1H), 2.81 (s, 3H), 3.21–3.24 (m, 1H), 3.56–
3.61 (m, 2H); 13C NMR (100 MHz, CDCl3): d=28.2, 28.3,
30.0, 35.1, 38.0, 39.5, 41.7, 49.7, 56.7, 68.0; MS (EI): m/z
(%)=216 (4%) [M+], 215 (28), 186 (35), 174 (16), 173 (21),
160 (100), 136 (46), 135 (22), 108 (10), 95 (12), 82 (17), 81
(31), 80 (13), 79 (23), 67 (22): HR-MS m/z=215.0989, calcd.
for C10H17NO2S [M]+: 215. 0980.
amide (5ca),[51] (E)-4-methyl-N-(3-methylpent-3-en-2-yl)ben-
ACHTUNGTRENNUNG
zenesulfonamide (5da).[21b]
Acknowledgements
This research has been supported by the DGES of the Span-
ish MICINN (Consolider INGENIO 2010 CSD2007-00006,
CTQ2007-62771/BQU, CTQ2010-20387 and CTQ2008-
06866-CO2-01), from the Generalitat Valenciana (Project
PROMETEO/2009/039), and by the University of Alicante.
G. K. is grateful to the Spanish MICINN for a “Juan de la
Cierva” contract. We also thank Dr. T. Soler for X-ray crys-
tallographic analyses.
4-Methyl-N-(1-methyltricyclo[2.2.1.02,6]heptan-3-yl)ben-
zenesulfonamide (8a): Yellow oil; Rf 0.31 (hexane/ethyl ace-
tate: 4/1); IR (KBr): n=3279, 2946, 2867, 1428, 1331, 1089,
1
870, 814, 662 cmÀ1; H NMR (400 MHz, CDCl3): d=0.77 (d,
J=4.9 Hz, 1H), 0.92 (d, J=4.9 Hz, 1H), 1.10 (s, 3H), 1.14–
1.17 (m, 1H), 1.30 (d, J=11.1 Hz, 1H), 1.53 (d, J=10.8 Hz,
1H), 1.81 (d, J=9.3 Hz, 1H), 2.42 (s, 3H), 3.28 (dt, J=7.32,
1.64 Hz, 1H), 4.89 (d, J=7.12 Hz, 1H), 7.29 (d, J=8.0 Hz,
2H), 7.78 (d, J=8.2 Hz, 2H); 13C NMR (100 MHz, CDCl3):
d=15.4, 17.7, 20.3, 21.5, 21.8, 30.5, 36.6, 37.2, 59.2, 127.0,
129.6, 138.1, 143.1; MS (EI): m/z (%)=277 (4) [M+], 122
(78), 120 (11), 107 (13), 106 (66), 105 (100), 95 (10), 94 (10),
92 (11), 91 (67), 81 (11), 80 (22), 79(20), 77 (16), 65 (18);
HR-MS: m/z=277.1128, calcd. for C15H19NO2S [M]+:
277.1136.
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ꢄ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3465

Xavier Giner et al.
FULL PAPERS
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