Gold catalysis contra platinum catalysis in hydroarylation contra phenol synthesis

Article abstract of DOI:10.1016/j.tet.2007.02.108

Three silylated γ-alkynylfurans were prepared and subjected to both gold and platinum catalysts. The TMS- and the TBDMS-substituted furans reacted. With AuCl₃ and the binuclear [(Ph₃PAu)₂Cl][BF₄] catalyst a hydroarylation of the alkyne was observed. Na[AuCl₄] gave phenols as the product, but these were formed only after in situ desilylation of the starting material by the gold catalyst and thus the wrong isomer dominated. Only with PtCl₂(MeCN)₂ phenols with a silyl group were formed. The TBDPS-substituted furan failed to react. Two alkynylsilanes were synthesized, but they also failed to react.

Full text of DOI:10.1016/j.tet.2007.02.108

Tetrahedron 63 (2007) 5879–5885
Gold catalysis contra platinum catalysis in hydroarylation
contra phenol synthesis
*
A. Stephen K. Hashmi, Elzen Kurpejovic, Wolfgang Frey and Jan W. Bats
´
Institut fu€r Organische Chemie, Universita€t Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
Received 15 January 2007; revised 22 February 2007; accepted 23 February 2007
Available online 28 February 2007
Abstract—Three silylated g-alkynylfurans were prepared and subjected to both gold and platinum catalysts. The TMS- and the TBDMS-
substituted furans reacted. With AuCl3 and the binuclear [(Ph3PAu)2Cl][BF4] catalyst a hydroarylation of the alkyne was observed. Na[AuCl4]
gave phenols as the product, but these were formed only after in situ desilylation of the starting material by the gold catalyst and thus the wrong
isomer dominated. Only with PtCl2(MeCN)2 phenols with a silyl group were formed. The TBDPS-substituted furan failed to react. Two
alkynylsilanes were synthesized, but they also failed to react.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
X
Au cat.
R1
O
X
R1
Gold catalysts have recently attracted significant atten-
tion.1,2 Among the new achievements in homogeneous
gold-catalyzed reactions2 the gold-catalyzed phenol synthe-
sis3 is one of the few examples of a previously unknown
reaction made possible by gold catalysts. It added a new
pathway to the family of the enyne cycloisomerization reac-
tions. But in competition with the cycloisomerization to the
phenols 2, the g-alkynylfurans 1 can also undergo a hydro-
arylation4 reaction, leading to anellated furans 3 (Scheme
1).3j,k One additional synthetic challenge was the synthesis
of phenols of type 2 without substituent in ortho-position
to the hydroxyl group (R1¼H), because the corresponding
furans, not possessing a substituent in 5-position of the furan
ring, usually deliver a mixture of the positional isomers 2
and 4, with 4 being the major component.
OH
+
for R1 = H
1
2
Au cat.
X
X
HO
4
R1
O
3
Scheme 1. Possible isomers from the phenol synthesis and competing
hydroarylation (X¼O, NR2, CR22).
and then a chlorosilane was added (Scheme 2). Subse-
quently, another lithiation of the 2-silylfurans 6 with
n-BuLi and formylation with DMF5 delivered the 5-silylfur-
furals 7. Crucial for the metallation was a temperature not
below 0 ꢀC and a reaction time not under 3 h, other experi-
ments were unsuccessful in our hands.
One concept was to block that position with a silyl group
(R1¼SiR23) as an auxiliary substituent, which on the other
hand might also serve as point for further functionaliza-
tion. Here we report our observations in the course of this
investigation.
The first experiment was done with the TMS-protected
8a. With AuCl3 as catalyst not the typical phenol but the
anellated furan 9a with an exocyclic double bond, the prod-
uct of an intramolecular hydroarylation,4 was formed
(Scheme 3).
2. Results and discussion
The substrates were easily available from furan (5). In the
first step it was lithiated with n-BuLi at room temperature
After 35–40 min, in situ NMR spectroscopy showed 65%
conversion, then the polymerization started. Therefore, it
was worked up before a complete conversion was reached
(a second sample after 24 h did not show signals of 9a any
more). Due to the sensitivity of the material and a quite sim-
ilar Rf value of 8a and 9a, a complete separation of 9a from
Keywords: Alkynes; Furans; Gold; Homogeneous catalysis; Phenols;
Silanes.
* Corresponding author. Tel.: +49 711 685 64330; fax: +49 711 685 64321;
e-mail: hashmi@hashmi.de
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.02.108

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A. S. K. Hashmi et al. / Tetrahedron 63 (2007) 5879–5885
1. n-BuLi, THF, r.t.
along with desilylated 12 in 27% yield. Since the silyl group
2. R1R22SiCl
3. H2O
was used in the sense of an auxiliary group anyway, this adds
to 53% of the products with the hydroxy group at the desired
position of the arene. Again 9a was observed as side-product
(Scheme 5).
O
O
R1R22Si
5
6
1. n-BuLi, THF, r.t.
2. DMF
3. H2O
6-7:
a R1, R2 = Me
b R1 = tBu, R2 = Me
c R1 = tBu, R2 = Ph
5 mol%
PtCl2(MeCN)2
R1R22Si
O
O
8a
NTs
CH3CN, 70 °C
9a (14%)
7
Me3Si
O
a 29% from 5a
b 65% from 5b
c 62% from 5c
+
NH2
1.
, MgSO4, DCM, 24 h, r.t.
NTs
NTs
2. NaBH4, MeOH, r.t., 2 h, then H2O
3. TsCl, NEt3, DCM, 48 h, r.t.
12 (27%)
OH
+
R1R22Si
O
NTs
Me3Si
13a (26%)
8
a 66%
b 65%
c 44%
OH
Scheme 5. Conversion of 8a with PtCl2(CH3CN)2 as catalyst.
Scheme 2. Preparation of the substrates 8a–c.
The structure of 13 could be confirmed by X-ray structure
analysis (Fig. 1).6 The aromatic ring is not perfectly planar.
The dihedral angle C2–C3–C4–C5 of 4.2 ꢀ results from the
stericrepulsionoftheOH–andthesilylgroup. Thustheatoms
Si1 and O1 deviate by 0.107 A (Si) and 0.070 A (O) from the
ideal plane of the aromatic core in opposite directions.
5 mol% AuCl3
NTs
8a
˚
˚
CD3CN
9a (60%)
O
Me3Si
Scheme 3. Reaction of the TMS-substituted furan 8a with AuCl3.
remaining substrate was not possible. Still the 1H NMR data
correlated well with the data of closely related substrates.3j
Na[AuCl4] also catalyzes the phenol synthesis, but is less ac-
tive and possesses a higher thermal stability. Indeed, with
Na[AuCl4] a different product distribution was observed;
the known3a phenols 11 and 12 were obtained in a ratio of
3:2, in addition significant amounts of the furan 10 were iso-
lated (Scheme 4).
Figure 1. Solid state structure of silylphenol 13a.
5 mol%
Na[AuCl4]
8a
O
NTs
NTs
NTs
CH3CN, 70 °C
10 (22%)
The last catalyst tested with 8a was the gold(I) complex
[(Ph3PAu)2Cl][BF4].3j The catalyst was very active, after
2 min the conversion was complete. The only product was
again the hydroarylation product 9a (Scheme 6). Pure 9a is
highly reactive, even in solution after two days at room tem-
perature an almost complete decomposition was observed.
+
+
HO
11
Σ 26%
ratio 60 : 40
5 mol%
12
OH
Scheme 4. Conversion of 8a with Na[AuCl4].
[(Ph3PAu)2Cl][BF4]
8a
NTs
9a (quantitative
in 2 minutes)
CH3CN, r.t.
Me3Si
O
The absence of silylated phenol indicated that the phenol
synthesis proceeded only after desilylation of the furan, the
ratio of 11:12 also corresponded to the value obtained from
the substrate not bearing a silyl group.3a
Scheme 6. Conversion of 8a with gold(I) catalyst [(Ph3PAu)2Cl][BF4].
Changing to 8b with the more stable tert-butyldimethylsilyl
group on the furan ring delivered a similar result with AuCl3.
Compound 9b with the exocyclic double bond (characteris-
tic 13C NMR signal of a vinylic methylene group at
112 ppm) was formed. Again, after about 60% conversion
a polymerization of the product became relevant (Scheme 7).
After testing a number of gold catalysts without much suc-
cess, with PtCl2(CH3CN)2 as catalyst for the phenol synthe-
sis,2b,c indeed the desired 13a was obtained (26% yield),

A. S. K. Hashmi et al. / Tetrahedron 63 (2007) 5879–5885
5881
Compound 15a could be characterized by a crystal structure
analysis (Fig. 2).6 Compounds 15a and 15b prove to be un-
reactive under the various conditions described above. Only
with 5 mol % Na[AuCl4] a partial desilylation and a subse-
quent formation of 11 and 12 from 15a in the same ratio
as shown in Scheme 4 was observed, 15b led to the known
phenol 16 (Scheme 10).
5 mol% AuCl3
CD3CN, r.t.
8b
NTs
tBuMe2Si
O
9b (60% after 35 minutes)
Scheme 7. Reaction of 8b with AuCl3 as the catalyst.
The reaction of 8b with PtCl2(CH3CN)2 also paralleled the
observations made with 8a and this catalyst. An almost iden-
tical yield of 12 and 13b (51% together) was obtained. In
addition 9b was formed (Scheme 8).
NTs
16
OH
Scheme 10. Compound 16 is formed from 15b by desilylation/isomeriza-
tion.
5 mol%
PtCl2(CH3CN)2
9b (14%)
8b
acetone, 70 °C
+
3. Conclusion
12 (25%)
+
Gold(I) catalysts efficiently serves as a hydroarylation cata-
lyst for the silylated g-alkynylfurans, while the platinum(II)
catalyst shows a high selectivity towards the phenolic prod-
ucts. Gold(III) catalysts shows a significant potential to serve
as a desilylation catalyst, which ultimately leads to a mixture
of hydroarylation and desilylated phenolic products.
NTs
tBuMe2Si
13b (26%)
OH
Scheme 8. Reaction of 8b with PtCl2(CH3CN)2 as the catalyst.
Compound 8c failed to undergo catalysis with either gold or
platinum catalysts. Since the large tert-butyldiphenylsilyl
group is too far from the reaction centre to shield it sterically,
the relative electron withdrawing nature of this group dimin-
ishes the nucleophilic reactivity of the furan ring and the
catalyst decomposes as the reaction is too slow.
4. Experimental
4.1. (5-Trimethylsilanyl)furan-2-carbaldehyde 7a
Furan (5.00 g, 73.4 mmol) in THF (50 ml) was stirred with
n-butyllithium (45.9 ml of a 1.6 M solution in hexane,
73.4 mmol) for 4 h at room temperature. Then trimethyl-
chlorosilane (10 ml, 11.6 g, 107 mmol) was added and stir-
ring was continued for 4 h at room temperature. After
hydrolysis it is extracted with diethyl ether (3ꢁ150 ml),
the combined extracts were dried over magnesium sulfate,
filtered and the solvent removed in vacuo. The residue was
taken up in THF (50 ml) and at room temperature n-butyl-
lithium (45.9 ml of a 1.6 M solution in hexane) was added.
After 4 h DMF (8.00 ml, 8.51 g, 116 mmol) was added.
After 1 h water (50 ml) was added. After extraction with di-
ethyl ether (3ꢁ150 ml) the extracts were dried over MgSO4,
filtered and the solvent was removed in vacuo. The residue
(3.58 g, 29%) was pure enough for the next steps. 1H NMR
(CDCl3, 300 MHz): d¼0.32 (s, 9H), 6.74 (d, J¼3.5 Hz, 1H),
7.21 (d, J¼3.5 Hz, 1H), 9.68 (s, 1H).
In order to further explore the behaviour of silyl groups in
these catalysis reactions, the alkynylsilanes 15a and 15b
were prepared as shown in Scheme 9.
1. n-BuLi, THF, -78 °C
O
NTs
O
NTs
R
R
2. TMSCl
3. H2O
Me3Si
14a (R = H)
14b (R = Me)
15a (R = H, 53%)
15b (R = Me, 79%)
Scheme 9. Preparation of the alkynylsilanes 15a and 15b.
4.2. 5-(tert-Butyldimethylsilanyl)-furan-
2-carbaldehyde 7b
Furan (2.50 g, 36.7 mmol) in THF (50 ml) was stirred with
n-butyllithium (23.0 ml of a 1.6 M solution in hexane,
36.7 mmol) for 4 h at room temperature. Then tert-butyldi-
methylchlorosilane (8.30 g, 55.1 mmol, 1.5 equiv) was
added and stirring was continued for 4 h at room temperature.
Water was added, after extractions with diethyl ether (3ꢁ
150 ml) the combined organic extracts were dried over mag-
nesium sulfate, filtered and the solvent removed in vacuo.
The residue was taken up in THF (50 ml) and n-butyllithium
(23.0 ml of a 1.6 M solution in hexane) was added. After 4 h
DMF (4.00 ml, 4.26 g, 58.3 mmol) was added and stirring
was continued for 1 h. Water (50 ml) was added, after
Figure 2. Solid state structure of 15a.

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A. S. K. Hashmi et al. / Tetrahedron 63 (2007) 5879–5885
extractions with diethyl ether (2ꢁ150 ml), the combined or-
ganic extracts were dried over MgSO4, filtered and the sol-
vent removed in vacuo. The brown residue (5.02 g, 65%)
was pure enough for the next steps. For analytical purposes
a small sample was purified by column chromatography to
deliver 7b as a yellow oil. Rf (petrol ether/ethyl acetate,
20:1)¼0.14. IR (film): ~n¼2936 cmꢂ1, 2857, 2812, 2359,
1734, 1683, 1559, 1463, 1369, 1258, 1215, 1109, 967, 928,
811, 774, 679. 1H NMR (CDCl3, 300 MHz): d¼0.26 (s, 6H),
0.91 (s, 9H), 6.75 (d, J¼3.5 Hz, 1H), 7.20 (d, J¼3.5 Hz, 1H),
9.67 (s, 1H). 13C NMR (CDCl3, 75.5 MHz): d¼ꢂ6.41 (q,
2C), 16.79 (s), 26.28 (q, 3C), 120.44 (d), 122.68 (d), 156.90
(s), 167.40 (s), 178.09 (d). MS (70 eV): m/z (%): 210 (8)
[M+], 182 (6), 153 (56), 125 (69), 75 (100). C11H18O2Si
(210.35): calcd C 62.81, H 8.63; found C 62.81, H 8.71.
triethylamine (902 mg, 8.91 mmol, 1.00 equiv) and tosyl
chloride (1.70 g, 8.91 mmol, 1.00 equiv) overnight. Water
(50 ml) was added, after extractions with DCM (3ꢁ100 ml),
the combined organic extracts were dried over MgSO4, fil-
tered and the solvent removed in vacuo. Column chromato-
graphy delivered 8a (2.12 g, 66%) as a yellow oil. Rf (petrol
ether/ethyl acetate, 20:1)¼0.13. IR (film): ~n¼3279 cmꢂ1
,
2945, 2230, 1679, 1590, 1481, 1420, 1340, 1320, 1293,
1240, 1172, 1151, 1078, 1045, 998, 925, 828, 792, 780, 637,
1
609. H NMR (CDCl3, 300 MHz): d¼0.20 (s, 9H), 2.07 (t,
J¼2.5 Hz, 1H), 2.42 (s, 3H), 4.01 (d, J¼2.5 Hz, 2H), 4.48
(s, 2H), 6.25 (d, J¼3.1 Hz, 1H), 6.50 (d, J¼3.1 Hz, 1H),
7.27 (d, J¼8.3 Hz, 2H), 7.73 (d, J¼8.3 Hz, 2H). 13C NMR
(CDCl3, 62.9 MHz): d¼ꢂ1.62 (q, 3C), 21.62 (q), 36.35 (t),
43.01 (t), 73.78 (d), 76.73 (s), 109.94 (d), 120.35 (d), 127.82
(d, 2C), 129.57 (d, 2C), 136.18 (s), 143.59 (s), 152.86 (s),
161.24 (s). MS (70 eV): m/z (%): 361 (11) [M+], 206
(100), 178 (42), 147 (14), 134 (29), 106 (8), 91 (35).
C18H23NO3SSi (361.54): calcd C 59.80, H 6.41, N 3.87;
found C 59.65, H 6.30, N 3.90.
4.3. (5-tert-Butyldiphenylsilanyl)furan-2-
carbaldehyde 7c
Furan (600 mg, 8.81 mmol) in THF (20 ml) was stirred with
n-butyllithium (5.51 ml of a 1.6 M solution in hexane,
8.81 mmol) for 4 h at room temperature. Then tert-butyl-
diphenylchlorosilane (2.91 g, 10.6 mmol, 1.2 equiv) was
added and stirring was continued for another 4 h at room
temperature. Water was added and after extractions with di-
ethyl ether (3ꢁ100 ml) the combined organic extracts were
dried over magnesium sulfate, filtered and the solvent re-
moved in vacuo. The residue was taken up in THF (50 ml)
and n-butyllithium (5.51 ml of a 1.6 M solution in hexane)
was added at room temperature. After 4 h DMF (2.00 ml,
2.13 g, 29.1 mmol) was added and stirring was continued
for 1 h. Water was added and after extractions with diethyl
ether (3ꢁ150 ml), the combined organic extracts were dried
over MgSO4, filtered and the solvent removed in vacuo. The
brown residue was filtered over a short silica gel column and
eluted with ethyl acetate. After removal of the solvent this
provided 7c as a yellow solid, which could be used in the
next step without further purification. Mp 83–85 ꢀC. Rf (pet-
4.5. N-[5-(tert-Butyldimethylsilanyl)furan-2-ylmethyl]-
4-methyl-N-prop-2-ynylbenzenesulfonamide 8b
Compound 7b (1.00 g, 4.75 mmol) in DCM (30 ml) was stir-
red with propargyl amine (790 mg, 14.3 mmol, 3.00 equiv)
and MgSO4 (4.00 g) overnight at room temperature. After
filtration the solvent was removed in vacuo, methanol
(30 ml) was added and sodium borohydride (180 mg,
4.75 mmol, 1.00 equiv) was added at room temperature. Af-
ter 2 h water (50 ml) was added, after extractions with DCM
(3ꢁ100 ml), the combined organic extracts were dried over
MgSO4, filtered and the solvent removed in vacuo. The resi-
due was taken up in DCM (30 ml), triethylamine (481 mg,
4.75 mmol, 1.00 equiv) and tosyl chloride (906 mg,
4.75 mmol, 1.00 equiv) were added and stirred overnight.
Water (50 ml) was added, after extractions with DCM (3ꢁ
100 ml), the combined organic extracts were dried over
MgSO4, filtered and the solvent removed in vacuo. Column
chromatography on silica gel delivered 8b (1.12 g, 65%) as
a yellow oil, which solidified at ꢂ25 ꢀC in the freezer to
a caramel-like solid with a melting point of 49 ꢀC. Mp 49–
50 ꢀC. Rf (petrol ether/ethyl acetate, 10:1)¼0.30. IR (film):
~n¼3301 cmꢂ1, 2927, 2855, 1769, 1596, 1465, 1347, 1297,
1252, 1214, 1186, 1157, 1092, 1065, 1017, 943, 897, 803,
770, 731, 659, 617, 575. 1H NMR (CDCl3, 500 MHz):
d¼0.17 (s, 6H), 0.87 (s, 9H), 2.08 (t, J¼2.5 Hz, 1H), 2.41
(s, 3H), 4.01 (d, J¼2.5 Hz, 2H), 4.47 (s, 2H), 6.27 (d,
J¼3.2 Hz, 1H), 6.53 (d, J¼3.2 Hz, 1H), 7.27 (d, J¼8.4 Hz,
2H), 7.72 (d, J¼8.4 Hz, 2H). 13C NMR (CDCl3, 126 MHz):
d¼ꢂ6.24 (q, 2C), 16.83 (s), 21.68 (q), 26.41 (q, 3C), 36.36
(t), 42.99 (t), 73.92 (d), 76.75 (s), 109.91 (d), 121.68 (d),
128.87 (d, 2C), 129.64 (d, 2C), 136.18 (s), 143.67 (s),
153.07 (s), 159.77 (s). MS (70 eV): m/z (%): 403 (32)
[M+], 346 (100), 248 (91), 190 (39), 149 (90), 91 (50).
C21H29NO3SSi (403.62): calcd C 62.42, H 7.24, N 3.47;
found C 62.46, H 7.32, N 3.38.
rol ether/ethyl acetate, 25:1)¼0.13. IR (film): ~n¼3066 cmꢂ1
,
2932, 2857, 2361, 1672, 1153, 1462, 1386, 1265, 1182,
1103, 1012, 962, 924, 818, 752, 697. H NMR (CDCl3,
1
300 MHz): d¼1.19 (s, 9H), 6.71 (d, J¼3.5 Hz, 1H), 7.25
(d, J¼3.5 Hz, 1H), 7.34–7.48 (m, 6H), 7.59–7.65 (m, 4H),
9.78 (s, 1H). 13C NMR (CDCl3, 62.9 MHz): d¼18.86 (s),
27.76 (q, 3C), 126.22 (d), 127.85 (d), 128.04 (d, 4C),
130.04 (d, 2C), 132.25 (s, 2C), 136.25 (d, 4C), 157.53 (s),
164.71 (s), 178.38 (d). MS (70 eV): m/z (%): 334 (3) [M+],
277 (68), 239 (36), 199 (75), 183 (100). HRMS (70 eV):
C21H22O2Si: calcd 334.1389; found 334.1388.
4.4. 4-Methyl-N-prop-2-ynyl-N-(5-trimethylsilanyl-
furan-2-ylmethyl)benzenesulfonamide 8a
Compound 7a (1.50 g, 8.91 mmol) in DCM (30 ml) was stir-
red with propargyl amine (1.47 g, 26.7 mmol, 3.00 equiv)
and MgSO4 (4.00 g) overnight at room temperature. After
filtration the solvent was removed in vacuo, the residue taken
up in methanol (30 ml) and sodium borohydride (337 mg,
8.91 mmol, 1.00 equiv) was added at room temperature. Af-
ter 2 h water was added (50 ml), after extractions with
DCM (3ꢁ100 ml), the combined organic extracts were dried
over MgSO4, filtered and the solvent removed in vacuo. The
residue was taken up in DCM (30 ml) and stirred with
4.6. N-[5-(tert-Butyldiphenylsilanyl)-furan-2-ylmethyl]-
4-methyl-N-prop-2-ynyl-benzenesulfonamide 8c
Compound 7c (1.00 g, 2.99 mmol) in DCM (30 ml) was
stirred with propargyl amine (500 mg, 9.99 mmol) and

A. S. K. Hashmi et al. / Tetrahedron 63 (2007) 5879–5885
5883
MgSO4 (4.00 g) at room temperature overnight. After filtra-
tion the solvent was removed in vacuo, the residue taken up
in methanol (30 ml) and sodium borohydride (113 mg,
2.99 mmol, 1.00 equiv) was added and stirred at room tem-
perature for 2 h. Water (50 ml) was added, after extractions
with DCM (100 ml), the combined organic extracts were
dried over MgSO4, filtered and the solvent removed in va-
cuo. The residue was taken up in DCM (30 ml) and stirred
with triethylamine (303 mg, 2.99 mmol, 1.00 equiv) and
tosyl chloride (570 mg, 2.99 mmol, 1.00 equiv) overnight.
Water (50 ml) was added, after extractions with DCM (3ꢁ
100 ml), the combined organic extracts were dried over
MgSO4, filtered and the solvent removed in vacuo. Column
chromatography on silica gel delivered 8c (694 mg, 44%) as
a yellow oil. Rf (petrol ether/ethyl acetate, 10:1)¼0.20. IR
(film): ~n¼3273 cmꢂ1, 2933, 2857, 1767, 1593, 1466, 1427,
1345, 1257, 1155, 1096, 1065, 1011, 893, 809, 738, 698,
657, 612, 577. 1H NMR (CDCl3, 300 MHz): d¼1.11 (s, 9H),
2.08 (t, J¼2.4 Hz, 1H), 2.38 (s, 3H), 4.04 (d, J¼2.4 Hz, 2H),
4.54 (s, 2H), 6.33 (d, J¼3.2 Hz, 1H), 6.53 (d, J¼3.2 Hz, 1H),
7.22 (d, J¼8.2 Hz, 2H), 7.30–7.44 (m, 6H), 7.55–7.60
(m, 4H), 7.72 (d, J¼8.2 Hz, 2H). 13C NMR (CDCl3,
62.9 MHz): d¼18.70 (s), 21.64 (q), 27.83 (q, 3C), 36.38
(t), 43.02 (t), 74.11 (d), 76.67 (s), 110.05 (d), 125.57 (d),
127.79 (d, 4C), 127.82 (d, 2C), 129.63 (d, 2C), 129.66 (d,
2C), 133.51 (s, 2C), 136.11 (s), 136.24 (d, 4C), 143.71 (s),
154.16 (s), 156.97 (s). MS (FAB positive-ion, matrix: 3-
nitrobenzylalcohol): m/z (%): 528 (16) [M++H], 527 (5)
[M+], 470 (64), 319 (100), 259 (27), 222 (75), 199 (46),
135 (38), 91 (17). HRMS (FAB positive-ion, matrix: 3-nitro-
benzylalcohol): [M+Na]+: calcd 550.1848; found 550.1830.
C31H33NO3SSi (527.76): calcd C 70.55, H 6.30, N 2.65;
found C 71.63, H 6.77, N 2.65.
overnight at 70 ꢀC. The solvent was removed in vacuo and
the crude product was purified by column chromatography
on silica gel. Thus starting material 8a (69 mg, 14%), 12
(108 mg, 27%)3a and 13 (131 mg, 26%) were obtained.
Crystals for the X-ray single crystal structure analysis
1
were obtained from ether/DCM. Compound 12: H NMR
(CD3CN, 300 MHz): d¼2.40 (s, 3H), 4.51–4.53 (m, 2H),
4.57–4.59 (m, 2H), 6.66 (d, J¼8.0 Hz, 1H), 6.71 (d,
J¼7.6 Hz, 1H), 7.09 (dd, J¼8.0 Hz, 7.6 Hz, 1H), 7.21 (s,
1H), 7.39 (d, J¼8.2 Hz, 2H), 7.77 (d, J¼8.2 Hz, 2H). 2-
(Toluene-4-sulfonyl)-5-trimethylsilanyl-2,3-dihydro-1H-iso-
indol-4-ol 13a: mp 166–168 ꢀC. Rf (petrol ether/ethyl
acetate, 10:1)¼0.08. IR (CDCl3): ~n¼3451 cmꢂ1, 2955,
1586, 1423, 1315, 1247, 1214, 1158, 1099, 1015, 885,
1
836, 763, 724, 659. H NMR (CDCl3, 500 MHz): d¼0.28
(s, 9H), 2.40 (s, 3H), 4.61 (m, 2H), 4.63 (m, 2H), 5.12 (s,
1H), 6.75 (d, J¼7.5 Hz, 1H), 7.23 (d, J¼7.5 Hz, 1H), 7.31
(d, J¼8.3 Hz, 2H), 7.76 (d, J¼8.3 Hz, 2H). 13C NMR
(CDCl3, 126 MHz): d¼ꢂ0.40 (q, 3C), 21.85 (q), 51.67 (t),
54.51 (t), 115.12 (d), 122.21 (s), 124.94 (s), 127.92 (d,
2C), 130.23 (d, 2C), 133.90 (s), 135.58 (d), 139.93 (s),
144.17 (s), 155.80 (s). MS (70 eV): m/z (%): 361 (29)
[M+], 277 (6), 206 (100), 163 (28), 91 (91). C18H23NO3SSi
(361.54): calcd: C 59.80, H 6.41, N 3.87; found: C 59.68, H
6.39, N 3.79.
4.9. 2-tert-Butylmethylsilanyl-4-methylene-6-(toluene-
4-sulfonyl)-4,5,6,7-tetrahydrofuro[2,3-c]pyridine 9b
The reaction of 8b (50.2 mg, 124 mmol) in CD3CN (0.5 ml)
with a stock-solution of AuCl3 in CD3CN (18.8 mg of
a 10 wt % solution, 1.88 mg, 6.20 mmol, 5 mol % AuCl3)
1
at room temperature was monitored by H NMR spectros-
copy. After 80 min the ratio of starting material to product
is 62:38. The reaction is very clean, but a complete conver-
sion is not even reached after 24 h. Instead, 9b starts to
decompose, then the ratio is 58:42. A DEPT 135 spectrum
shows the characteristic olefinic methylene group at
4.7. 4-Methylene-6-(toluene-4-sulfonyl)-2-trimethyl-
silanyl-4,5,6,7-tetrahydrofuro[2,3-c]pyridine 9a
To 8a (100 mg, 277 mmol) and CD3CN (0.5 ml) in an NMR
tube a stock-solution of AuCl3 in CD3CN (42.0 mg contain-
ing 10 wt % AuCl3, 4.20 mg, 13.8 mmol, 5 mol % AuCl3)
was added at room temperature. The reaction was monitored
by 1H NMR spectroscopy. After 30 min 65% of the starting
material was consumed, the reaction was worked up because
the product started to polymerize (a second sample was not
worked up, after 24 h no more product 9a was detectable in
the NMR, only very broad, unspecific peaks were visible).
The solvent was removed in vacuo and the residue was puri-
fied by column chromatography on silica gel. Thus 9a
(59.6 mg, 60%) was obtained. Rf (petrol ether/ethyl acetate,
20:1)¼0.12. IR (film): ~n¼2958 cmꢂ1, 2362, 1654, 1349,
1
122 ppm. H NMR (CD3CN, 300 MHz): d¼0.20 (s, 6H),
0.91 (s, 9H), 2.34 (s, 3H), 4.06 (t, J¼1.4 Hz, 2H), 4.44 (s,
2H), 4.94–4.97 (m, 1H), 5.02–5.05 (m, 1H), 6.66 (s, 1H),
7.23 (d, J¼8.2 Hz, 2H), 7.61 (d, J¼8.2 Hz, 2H).
4.10. Reaction of 8b with PtCl2(CH3CN)2
Compound 8b (95.0 mg, 235 mmol) in acetone-d6 and
PtCl2(CH3CN)2 (4.11 mg, 11.8 mmol, 5 mol %) were heated
to 60 ꢀC overnight. Then the solvent was removed in vacuo
and the residue was purified by column chromatography
on silica gel. Thus 9b (12 mg, 13%), 12 (17 mg, 25%) and
13b (25 mg, 26%) were obtained. 5-(tert-Butyldimethylsi-
lanyl)-2-(toluene-4-sulfonyl)-2,3-dihydro-1H-isoindol-4-ol
13b: Rf (petrol ether/ethyl acetate, 10:1)¼0.10. IR (film):
~n¼3266 cmꢂ1, 2929, 2856, 2362, 1713, 1600, 1468, 1291,
1256, 1156, 1092, 1007, 815, 666. 1H NMR (CDCl3,
500 MHz): d¼0.31 (s, 6H), 0.87 (s, 9H), 2.40 (s, 3H), 4.61
(s, 4H), 5.18 (br s, 1H), 6.75 (d, J¼7.5 Hz, 1H), 7.21 (d,
J¼7.5 Hz, 1H), 7.31 (d, J¼8.3 Hz, 2H), 7.77 (d, J¼8.3 Hz,
2H). 13C NMR (CDCl3, 75.5 MHz): d¼ꢂ4.50 (q, 2C),
17.70 (s), 21.63 (q), 26.70 (q, 3C), 51.60 (t), 54.30 (t),
114.60 (d), 121.57 (s), 122.49 (s), 127.74 (d, 2C), 129.97
(d, 2C), 133.79 (s), 136.71 (d), 139.78 (s), 143.84 (s),
155.88 (s). MS (70 eV): m/z (%): 403 (6) [M+], 346 (100),
1
1251, 1163, 1093, 1045, 924, 841, 758. H NMR (CDCl3,
300 MHz): d¼0.22 (s, 9H), 2.37 (s, 3H), 3.98 (t,
J¼1.3 Hz, 2H), 4.39 (s, 2H), 4.89 (mc, 1H), 5.00 (mc, 1H),
6.50 (s, 1H), 7.20 (d, J¼8.4 Hz, 2H), 7.62 (d, J¼8.4 Hz,
2H). 13C NMR (CDCl3, 75.5 MHz): d¼ꢂ1.58 (q, 3C), 21.58
(q), 44.35 (t), 49.76 (t), 106.85 (t), 115.53 (d), 118.39 (s),
127.69 (d, 2C), 129.50 (d, 2C), 132.84 (s), 134.05 (s), 151.14
(s), 160.87 (s), one C (s) not detected.
4.8. Reaction of 8a with PtCl2(CH3CN)2
Compound 8a (500 mg, 1.38 mmol) in acetone (5 ml) and
PtCl2(CH3CN)2 (24 mg, 69 mmol, 5 mol %) were stirred

5884
A. S. K. Hashmi et al. / Tetrahedron 63 (2007) 5879–5885
229 (16), 190 (32), 163 (50), 91 (49). HRMS (70 eV):
C21H29NO3S: calcd 403.1637; found: 403.1632.
C21H29NO3S (403.62):calcd: C 62.49, H 7.24, N 3.47; found:
C 60.32, H 7.23, N 2.94.
Acknowledgements
This work was supported by the Deutsche Forschungs-
gemeinschaft (Ha 1932/10-1), the Fonds der Chemischen
Industrie and Umicore AG & Co. KG.
4.11. N-Furan-2-ylmethyl-4-methyl-N-(3-trimethyl-
silanyl-prop-2-ynyl)-benzenesulfonamide 15a
To 14a3a (920 mg, 3.17 mmol) in THF (15 ml) at ꢂ78 ꢀC
n-butyllithium (2.00 ml of a 1.6 M solution in hexane,
3.20 mmol) was added. After stirring at that temperature
for 30 min, the reaction mixture was warmed to 0 ꢀC and
trimethylsilylchloride (1.2 ml, 1.03 g, 9.50 mmol) was
added. Water was added (10 ml), after extractions with
DCM (3ꢁ15 ml), the combined organic extracts were dried
over magnesium sulfate, filtered and the solvent was re-
moved in vacuo. Column chromatography delivered 15a
(610 mg, 53%) as a colourless solid. By evaporation of a so-
lution in petrol ether/DCM single crystals for a crystal struc-
ture analysis were obtained. Mp 83 ꢀC. Rf (petrol ether/ethyl
References and notes
1. For milestone examples from heterogeneous catalysis, see: (a)
Haruta, M.; Kobayashi, T.; Sano, H.; Yamada, N. Chem. Lett.
1987, 16, 405–408; (b) Hutchings, G. J. J. Catal. 1985, 96,
292–295; (c) Abad, A.; Concepcion, P.; Corma, A.; Garcia, H.
Angew. Chem. 2005, 117, 4134–4137; Angew. Chem., Int. Ed.
2005, 44, 4066–4069.
2. For reviews on homogeneous catalysis, see: (a) Dyker, G.
Angew. Chem. 2000, 112, 4407–4409; Angew Chem., Int. Ed.
2000, 39, 4237–4239; (b) Hashmi, A. S. K. Gold Bull. 2003,
36, 3–9; (c) Hashmi, A. S. K. Gold Bull. 2004, 37, 51–65; (d)
acetate/DCM, 18:1:1)¼0.18. IR (KBr): ~n¼3030 cmꢂ1
,
Krause, N.; Hoffmann-Roder, A. Org. Biomol. Chem. 2005, 3,
€
2930, 2900, 1491, 2145, 1590, 1339, 1320, 1236, 1155,
997, 983, 876, 832, 749, 730, 646. 1H NMR (CDCl3,
500 MHz): d¼0.00 (s, 9H), 2.41 (s, 3H), 4.02 (s, 2H), 4.40
(s, 2H), 6.27 (m, 2H), 7.27 (d, J¼8.2 Hz, 2H), 7.34 (d,
J¼0.9 Hz, 1H), 7.72 (d, J¼8.2 Hz, 2H). 13C NMR (CDCl3,
126 MHz): d¼ꢂ0.37 (q, 3C), 21.56 (q), 37.18 (t), 42.78
(t), 91.26 (s), 97.69 (s), 109.94 (d), 110.40 (d), 127.81 (d,
2C), 129.55 (d, 2C), 135.98 (s), 142.98 (d), 143.49 (s),
148.67 (s). MS (70 eV): m/z (%)¼361 (1) [M+], 346 (3),
322 (2), 288 (3), 250 (4), 206 (100), 177 (7), 155 (6), 133
(16), 111 (3), 91 (14), 81 (48), 73 (34), 53 (8).
C18H23NO3SSi (361.5): calcd C 59.80, H 6.41, N 3.87;
found C 59.91, H 6.38, N 3.84.
387–391; (e) Hashmi, A. S. K. Angew. Chem. 2005, 117,
7150–7154; Angew. Chem., Int. Ed. 2005, 44, 6990–6993; (f)
Zhang, L.; Sun, J.; Kozmin, S. A. Adv. Synth. Catal. 2006,
348, 2271–2296; (g) Hashmi, A. S. K.; Hutchings, G. Angew.
Chem. 2006, 118, 8064–8105; Angew. Chem., Int. Ed. 2006,
45, 7836–7896.
3. (a) Hashmi, A. S. K.; Frost, T. M.; Bats, J. W. J. Am. Chem. Soc.
ꢀ
2000, 122, 11553–11554; (b) Martın-Matute, B.; Cardenas,
D. J.; Echavarren, A. M. Angew. Chem. 2001, 113, 4890–
4893; Angew. Chem., Int. Ed. 2001, 40, 4754–4757; (c)
Hashmi, A. S. K.; Frost, T. M.; Bats, J. W. Org. Lett. 2001, 3,
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3769–3771; (d) Mendez, M.; Munoz, M. P.; Nevade, C.;
Cardenas, D. J.; Echavarren, A. M. J. Am. Chem. Soc. 2001,
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123, 10511–10520; (e) Hashmi, A. S. K.; Frost, T. M.; Bats,
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Ding, L.; Fischer, P.; Bats, J. W.; Frey, W. Chem.—Eur. J.
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4.12. 4-Methyl-N-(5-methylfuran-2-ylmethyl)-N-(3-tri-
methylsilanylprop-2-ynyl)benzenesulfonamide 15b
To 14b3a (1.00 g, 3.30 mmol) in THF (30 ml) at ꢂ78 ꢀC
n-butyllithium (2.06 ml of a 1.6 M solution in hexane,
3.30 mmol) was added. After stirring for 30 min an excess
of trimethylsilylchloride was added and the reaction mixture
slowly warmed to room temperature. Water (50 ml) was
added, after extraction with DCM (3ꢁ60 ml), the combined
organic extracts were dried over MgSO4, filtered and the
solvent removed in vacuo. Column chromatography deliv-
ered 15b (978 mg, 79%) as a colourless solid. Mp 81–
82 ꢀC. Rf (petrol ether/ethyl acetate/DCM; 10:1:1)¼0.42.
IR (KBr): ~n¼2930 cmꢂ1, 2895, 2865, 2143, 1914, 1668,
1589, 1542, 1431, 1340, 1322, 1238, 1152, 1100, 1078,
1046, 1003, 985, 956, 875, 930, 793, 762, 746, 717, 643.
1H NMR (CDCl3, 500 MHz): d¼0.01 (s, 9H), 2.22 (d,
J¼1.1 Hz, 3H), 2.42 (s, 3H), 4.02 (s, 2H), 4.35 (s, 2H),
5.86 (qd, J¼3.1 Hz, 1.1 Hz, 1H), 6.14 (d, J¼3.1 Hz, 1H),
7.28 (d, J¼8.2 Hz, 2H), 7.74 (d, J¼8.2 Hz, 2H). 13C NMR
(CDCl3, 125 MHz): ꢂ0.41 (q, 3C), 13.55 (q), 21.50
(q), 36.99 (t), 42.86 (t), 91.07 (s), 97.78 (s), 106.20 (d),
110.95 (d), 127.79 (d, 2C), 129.44 (d, 2C), 136.00 (s),
143.34 (s), 146.43 (s), 152.77 (s). MS (70 eV): m/z (%):
375 (10) [M+], 302 (4), 266 (6), 220 (100), 191 (30), 147
(13), 95 (48), 91 (10), 73 (21). C19H25NO3SSi (375.57):
calcd C 60.76, H 6.71, N 3.73; found C 60.57, H 6.61,
N 3.70.
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Tetrahedron 1985, 41, 3803–3812.

A. S. K. Hashmi et al. / Tetrahedron 63 (2007) 5879–5885
5885
6. Crystallographic data (excluding structure factors) for the
structures in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication nos. CCDC 633391, 633692. Copies of the
data can be obtained, free of charge, on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK,
(fax: +44 (0) 1223 336033 or e-mail: deposit@ccdc.cam.
ac.uk).