Gold catalysis: Mild conditions for the transformation of alkynyl epoxides to furans

Article abstract of DOI:10.1002/adsc.200303201

GoLd(III) chloride catalyzes the isomerization of alkynyl epoxides to furans under mild conditions. Additional functional groups like hydroxy groups or aryl bromides do not need to be protected.

Full text of DOI:10.1002/adsc.200303201

FULL PAPERS
Gold Catalysis: Mild Conditions for the Transformation of
Alkynyl Epoxides to Furans
A. Stephen K. Hashmi,* Pradipta Sinha
Institut f¸r Organische Chemie, Universit‰t Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
Fax: ( ‡ 49)-711-685-4321, e-mail: hashmi@hashmi.de
Received: November 5, 2003; Accepted: February 11, 2004
Abstract: Gold(III) chloride catalyzes the isomeriza- Keywords: alkynes; epoxides; furans; gold; homoge-
tion of alkynyl epoxides to furans under mild neous catalysis
conditions. Additionalfunctionalgroups ilke hydroxy
groups or arylbromides do not need to be protected.
Introduction
isomerization but rather by the reaction with an external
carbon nucleophile, is palladium-catalyzed and was
Furans are an important class of heterocyclic com- published by Tsuji et al. in 1987.[14]
pounds which are extensively used as synthetic building
These approaches to furan in principle allow a perfect
blocks[1] and appear as a subunit in many natural regiocontrolin the synthesis of 2-, 3-, 2,3-, 2,4-, 2,5-,
products and substances of relevance for industry.[2] 2,3,5- and even 2,3,4,5-substituted furans. But the
Thus the synthesis of furans has always been of reactions mentioned above also have some limitations.
importance.[3]
The disadvantages of the Hg-catalysis are obvious, the
À
Since alkynyloxiranes are nowadays easily accessible base-catalysis depends on a C H bond in the propar-
by either a Sonogashira coupling[4] of an alkyne and a gylic position and therefore allows the synthesis of
vinylhailde and a subsequent epoxidation [5] or nucleo- furans which possess a substituent in the 2-position, the
philic ring closure of propargylic alcohols with a leaving latter is also true for the SmI2. Furthermore, the catalysis
group in the homopropargylic position,[6] the isomer- by the strong bases will also be problematic when other
ization of alkynyloxiranes to furans looks quite attrac- eliminations are possible or epimerizations of chiral
tive, especially for highly substituted furans. Thus centers are possible. The molybdenum and ruthenium
severalgroups have arleady addressed this rearrange-
catalysts are limited to a terminal alkyne in the substrate
ment. In 1975 Queguiner et al.[7] and in 1981 Berbalk for the formation of the intermediate vinylidene species.
et al. described the Hg(II)/acid-catalyzed reaction.[8] We were looking for a catalyst that had the potential of
Queguiner et al. also reported an isomerization by the Hg catalyst without using this problematic metal,
NaOEt in ethanol.[7b] Ten years later Marshall et al. would not need terminal alkynes and would work under
discovered that this rearrangement can also be induced less acidic or, respectively, less basic conditions. In the
by stoichiometric amounts of base using either potas- context of the recent investigation of the addition of
sium hydride in THF/HMPA at room temperature or heteronucleophiles to alkynes,[15] we have now inves-
KOt-Bu/18-crown-6 in t-BuOH at 608C.[9] This reaction tigated AuCl3 as a catalyst for this transformation.
is initiated by an elimination to an cumulenyl alkoxide
and thus depended on the propargylic position. Similar
results with in situ formed alkynyloxiranes were ob- Results and Discussion
tained by Katrizky et al.[10] A related class of starting
materials, alkynyloxiranes with leaving groups in the The synthesis of the starting materials followed the
propargylic position, furnished furans upon treatment sequence mentioned above. Sonogashira coupling of 1
with stoichiometric amounts of SmI2 and catalytic and 2 afforded the 1,3-enynes 3. Epoxidation of the
amounts of Pd(0) or Pd(II) in the case of a sequential latter with mCPBA yielded the alkynyloxiranes 4
procedure developed by Aurrechoechea et al.[11] Finally, (Scheme 1).
in 1994 McDonald et al.[12] reported a molybdenum-
Compound 4 was then subjected to a catalytic amount
catalyzed and last year Liu et al.[13] reported a ruthe- of AuCl3 in acetonitrile at room temperature. The
nium-catalyzed isomerization of alkynyloxiranes with a conversions of 4a (entry 1) and 4b (entry 2) proceeded
terminalaklyne to the corresponding furan. Another
in high yields, the primary alcohol group did not cause
reaction that converts alkynyl epoxides to furans, not by any problems (Table 1).
432
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/adsc.200303201
Adv. Synth. Catal. 2004, 346, 432 438

Transformation of Alkynyl Epoxides to Furans
FULL PAPERS
Table 1. Yield of the gold-catalyzed isomerization of 4 to 5.
Entry
Starting material
Product (isolated yield)
1
2
3
4
5
6
7
4a
4b
4c
4d
4e
4f
5a (80%)
5b (84%)
5c (56%)
5d (53%)
5e (25%)
5f (25%)
5g (0%), 6 (69%)
4g
deprotection of the aldehyde taking place in the second
phase of the reaction when the furan was already formed
and the acetal is activated by the furyl (benzyl-like)
position. Usually it is synthetically challenging to
position a formylgroup in the 4-position of the furan
ring.
For the mechanism of the reaction we assume that like
in many other cases[16] the gold activates the carbon-
carbon triple bond for the addition of a nucleophile by
co-ordination as shown in 7. In this case the epoxide-
oxygen would attack at the distal position of the alkyne,
the gold will form a s-bond to the other carbon atom of
the alkyne and the resulting species 8 only has to loose a
proton to form the aromatic furan 9 and finally the
product 5 after proto-demetallation (Scheme 2).
If the mechanism depicted in Scheme 2 is correct, one
proton must migrate to the 3- or 4-position of the furan
ring during the reaction. Thus the maximum number of
substituents on the furan ring tolerated by this reaction
would be three. Further studies are needed to clarify this
point.
Scheme 1. Sequence to the alkynyl epoxides 4 and their gold-
catalyzed isomerization to 5.
With the arylsubstituent in 4c and 4d, the yield
dropped to 56% (entry 3) and 53% (entry 4). The same
is true for 4e and 4f (25%, entries 5 and 6), which
suggests that the low yield is connected to the (CH2)OH
substituent in all the substrates 4c f (for example, an
elimination followed by a polymerization of the vinyl-
furan).
Quite nice is the reaction of the diethylacetal 4g,
where the isomerization to the furan is connected with a
deprotection of the furylic acetal to the furylaldehyde 6
in 67% yield overboth steps (entry 7). The NMR spectra
Scheme 2. Mechanistic proposal for the gold-catalyzed iso-
taken during the reaction provide evidence for the merization of 4 to 5.
Adv. Synth. Catal. 2004, 346, 432 438
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¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
433

A. Stephen K. Hashmi, Pradipta Sinha
FULL PAPERS
Conclusion
pound 5a was obtained as a yellow viscous liquid; yield: 24.1 mg
(80%). IR (film): n ˆ 3375, 2946, 2887, 2363, 1141, 1072,
1037 cmÀ1; 1H NMR (CDCl3, 500 MHz): d ˆ 7.06 (s, 1H), 5.88
(s, 1H), 3.68 (t, J ˆ 7.45 Hz, 2H), 2.68 (m, 2H), 1.98 (s, 3H), 1.88
(m, 2H), 1.48 (br s, 1H, OH); 13C NMR (CDCl3, 125 MHz): d ˆ
155.89 (s), 137.85 (d), 120.84 (s), 108.26 (d), 62.46 (t), 31.33 (t),
In conclusion, with gold(III) chloride the isomerization
is possible under mild conditions and tolerates a number
of functionalgroups.
‡
24.73 (t), 10.12 (q); MS (EI, 70 eV): m/z (%) ˆ 140 (62) [M ],
122 (37), 109 (12), 95 (100); HRMS (70 eV): calcd. for C8H12O2
‡
(M ): 140.0837; found: 140.0841; anal. calcd. for C8H12O2: C
68.55, H 8.63; found: C 67.54, H 8.62.
Experimental Section
6-Methylhept-6-en-4-yn-1-ol (3a)
7-Methyloct-7-en-5-yn-1-ol (3b)
To
a stirred solution of 2-bromopropene (1a; 1.81 g,
The compound 3b was obtained from 5-hexyn-1-ol( 2b; 393 mg,
4.00 mmol) and triethylamine (911 mg, 9.00 mmol) in THF
(4 mL), CuI (45.7 mg, 240 mmol), (PPh3)2PdCl2 (84.2 mg,
120 mmol) and 1a (1.45 g, 12.0 mmol) in THF (4 mL) as
described for 3a. Column chromatography (silica gel, 10%
EtOAC-hexane) afforded 3b as a yellow viscous liquid; yield:
459 mg (83%). IR (film): n ˆ 3320, 3070, 2920, 2840, 2190,
1610 cmÀ1; 1H NMR (CDCl3, 500 MHz): d ˆ 5.19 (d, J ˆ
1.65 Hz, 1H), 5.13 (d, J ˆ 1.65 Hz, 1H), 3.68 (t, J ˆ 6.2 Hz,
2H), 2.34 (t, J ˆ 6.8 Hz, 2H), 1.86 (s, 3H), 1.69 (m, 2H), 1.63 (m,
2H), 1.48 (s, 1H, OH); 13C NMR (CDCl3, 125 MHz): d ˆ 127.53
(s), 120.83 (d), 89.23 (s), 82.54 (s), 62.78 (t), 32.19 (t), 25.31 (t),
15.0 mmol) and triethylamine (1.52 g, 15.0 mmol) in THF
(5 mL), CuI (76.1 mg, 400 mmol) and (PPh3)2PdCl2 (140 mg,
200 mmol) were added. A solution of 4-pentyn-1-ol (2a;
84.1 mg, 10.0 mmol) in THF (5 mL) was added dropwise at
room temperature. The reaction mixture was allowed to stir at
room temperature for 17 h. The solvent was evaporated and
the column chromatography of the crude product (silica gel,
10% EtOAC-hexane) afforded 3a as a yellow viscous oil; yield:
1.13 g (91%). IR (film): n ˆ 3350, 3080, 2930, 2860, 2200,
1610 cmÀ1; 1H NMR (CDCl3, 500 MHz): d ˆ 5.19 (d, J ˆ
1.7 Hz, 1H), 5.14 (d, J ˆ 1.7 Hz, 1H), 3.76 (t, J ˆ 6.1 Hz, 2H),
2.43 (t, J ˆ 6.1 Hz, 2H), 1.86 (s, 3H), 1.79 (m, 2H), 1.58 (s, 1H,
OH); 13C NMR (CDCl3, 125 MHz): d ˆ 127.39 (s), 121.02 (d),
88.76 (s), 82.76 (s), 62.14 (t), 31.66 (t), 24.09 (q), 16.18 (t); MS
‡
24.15 (q), 19.36 (t); MS (EI, 70 eV): m/z (%) ˆ 138 (26) [M ],
123 (19), 109 (29), 91 (57), 79 (100); anal. calcd. for C9H14O: C
78.21, H 10.21; found: C 78.61, H 10.11.
‡
(EI, 70 eV): m/z (%): 124 (36)[M ], 105 (25), 91 (100), 79 (56),
65 (23), 53 (23), 41 (16); anal. calcd. for C8H12O: C 77.38, H 9.74;
found: C 77.26, H 9.73.
6-(2-Methyloxiranyl)hex-5-yn-1-ol (4b)
The compound 4b was obtained using 3b (276 mg, 2.00 mmol)
and Na2HPO4 (710 mg, 5.00 mmol) in DCM (8 mL) and
mCPBA (725 mg, 4.20 mmol) as described for 4a. Column
chromatography (silica gel, 15% EtOAC-hexane) furnished
pure compound 4b as a colorless viscous liquid; yield: 212 mg
(69%). IR (film): n ˆ 3360, 3040, 2920, 2850, 2210, 1260 cmÀ1;
1H NMR (CDCl3, 500 MHz): d ˆ 3.63 (t, J ˆ 6.1 Hz, 2H), 2.93
(d, J ˆ 5.6 Hz, 1H), 2.71 (d, J ˆ 5.6 Hz, 1H), 2.21 (t, J ˆ 6.9 Hz,
2H), 1.71 (br s, 1H, OH), 1.63 (m, 2H), 1.56 (m, 2H), 1.50 (s,
3H); 13C NMR (CDCl3, 125 MHz): d ˆ 82.99 (s), 80.11 (s),
61.56 (t), 55.88 (t), 47.85 (s), 32.03 (t), 24.96 (t), 23.60 (q), 16.70
5-(2-Methyloxiranyl)pent-4-yn-1-ol (4a)
To a stirred solution of 3a (124 mg, 1.00 mmol) and Na2HPO4
(350 mg, 2.47 mmol) in DCM (5 mL) was added mCPBA
(362 mg, 2.10 mmol) at 08C. The reaction mixture was stirred
at 08C for 3 h and then allowed to warm to room temperature,
whereupon it was diluted with ether and quenched with
aqueous saturated NaHCO3 solution. The organic layer was
washed with 10% NaOH, brine and finally dried over
anhydrous MgSO4. The solvent was evaporated and column
chromatography (silica gel, 15% EtOAC-hexane) afforded 4a
as a colorless viscous oil; yield: 82.0 mg (59%). IR (film): n ˆ
‡
(t); MS (EI, 70 eV): m/z (%) ˆ 154 (21) [M ], 123 (55), 109 (25),
1
3360, 3040, 2920, 2860, 2220, 1260 cmÀ1; H NMR (CDCl3,
95 (92), 91 (100), 81 (26), 67 (53), 57 (9); anal. calcd. for
C9H14O2: C 70.10, H 9.15; found: C 69.74, H 9.07.
500 MHz): d ˆ 3.66 (t, J ˆ 6.2 Hz, 2H), 2.92 (d, J ˆ 5.6 Hz, 1H),
2.69 (d, J ˆ 5.6 Hz, 1H), 2.27 (t, J ˆ 7.1 Hz, 2H), 2.21 (br s, 1H,
OH), 1.69 (m, 2H), 1.48 (s, 3H); 13C NMR (CDCl3, 125 MHz):
d ˆ 82.59 (s), 80.15 (s), 61.56 (t), 55.82 (t), 47.83 (s), 31.29 (t),
4-(4-Methylfuran-2-yl)butan-1-ol (5b)
‡
23.51 (q), 15.38 (t); MS (EI, 70 eV): m/z (%) ˆ 140 (3)[M ], 125
A solution of AuCl3 in MeCN (255 mg; 5% w/w, 12.8 mg,
42.0 mmolAuCl 3) was added to a solution of 4b (130 mg,
843 mmol) in MeCN (1 mL) at 258C. After 17 h (the reaction
was monitored by thin layer chromatography) the solvent was
evaporated and residue was purified by column chromatog-
raphy (silica gel, 10% EtOAC-hexane). The pure compound 5b
was obtained in as a colorless viscous liquid; yield: 109 mg
(84%). IR (film): n ˆ 3320, 2920, 2850, 1610, 1100, 1040 cmÀ1;
1H NMR (CDCl3, 500 MHz): d ˆ 7.05 (s, 1H), 5.86 (s, 1H), 3.66
(t, J ˆ 6.4 Hz, 2H), 2.60 (m, J ˆ 7.3 Hz, 2H), 1.97 (s, 3H), 1.69
(m, 2H), 1.61 (m, 2H), 1.36 (br s, 1H, OH); 13C NMR (CDCl3,
125 MHz): d ˆ 156.35 (s), 137.69 (d), 120.78 (s), 108.09 (d),
(3), 109 (27), 95 (11), 82 (100), 70 (3); anal. calcd. for C8H12O2: C
68.55, H 8.63; found: C 68.72, H 8.57.
3-(4-Methylfuran-2-yl)propan-1-ol (5a)
A solution of AuCl3 in MeCN (66.1 mg; 5% w/w; 3.30 mg,
10.8 mmolAuCl 3) was added to a solution of 4a (30.0 mg,
214 mmol) in MeCN (0.5 mL) at 258C. After 17 h (the reaction
was monitored by thin layer chromatography) the solvent was
evaporated and the residue was purified by column chroma-
tography (silica gel, 12% EtOAC-hexane). The pure com-
434
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2004, 346, 432 438

Transformation of Alkynyl Epoxides to Furans
FULL PAPERS
63.02 (t), 32.51 (t), 28.09 (t), 24.59 (t), 10.14 (q); MS (EI, 70 eV):
5-(4-Bromophenyl)-3-methylenepent-4-yn-1-ol (3d)
‡
m/z (%) ˆ 154 (54) [M ], 108 (49), 95 (100), 84 (15), 67 (15), 41
The compound 3d was obtained using 1b (680 mg, 4.50 mmol)
and triethylamine (683 mg, 6.75 mmol) in THF (3 mL), CuI
(34.3 mg, 180 mmol), (PPh3)2PdCl2 (63.2 mg, 90.0 mmol) and 1-
bromo-4-ethynylbenzene (2d; 905 mg, 5.00 mmol) in THF
(3 mL) as described for 3a. Column chromatography (silica gel,
10% EtOAC-hexane) afforded 3d as a yellow solid; yield:
418 mg (37%). IR (film): n ˆ 3360, 2840, 1600, 800, 580 cmÀ1;
1H NMR (CDCl3, 500 MHz): d ˆ 7.39 (d, J ˆ 8.4 Hz, 2H), 7.26
(d, J ˆ 8.4 Hz, 2H), 5.51 (d, J ˆ 1.2 Hz, 1H), 5.39 (d, J ˆ 1.2 Hz,
1H), 3.82 (t, J ˆ 6.2 Hz, 2H), 2.46 (t, J ˆ 6.2 Hz, 2H), 1.74 (br s,
1H, OH); 13C NMR (CDCl3, 125 MHz): d ˆ 133.32 (d, 2C),
131.92 (d, 2C), 128.09 (s), 124.56 (t), 122.94 (s), 122.16 (s), 90.29
(s), 89.07 (s), 61.12 (t), 40.69 (t); MS (EI, 70 eV): m/z (%) ˆ 252
(13); anal. calcd. for C9H14O2: C 70.10, H 9.15; found: C 69.57, H
9.18.
3-Methylene-5-phenylpent-4-yn-1-ol (3c)
The compound 3c was obtained from 3-bromo-3-buten-1-ol
(1b; 604 mg, 4.00 mmol) and triethylamine (607 mg,
6.00 mmol) in THF (3 mL), CuI (30.5 mg, 160 mmol),
(PPh3)2PdCl2 (56.2 mg, 80.0 mmol) and phenylacetylene (2c;
540 mg, 6.00 mmol) in THF (3 mL) in analogy to 3a. Column
chromatography (silica gel, 10% EtOAC-hexane) furnished
pure compound 3c as a yellow viscous liquid; yield: 490 mg
(71%). IR (film): n ˆ 3070, 3040, 2860, 2220, 1650, 1600 cmÀ1;
1H NMR (CDCl3, 500 MHz): d ˆ 7.43 (m, 2H), 7.32 (m, 3H),
5.55 (d, J ˆ 1.1 Hz, 1H), 5.41 (d, J ˆ 1.1 Hz, 1H), 3.88 (t, J ˆ
6.0 Hz, 2H), 2.52 (t, J ˆ 6.1 Hz, 2H), 1.62 (br s, 1H, OH);
13C NMR (CDCl3, 125 MHz): d ˆ 131.94 (d, 2C), 128.74 (d),
128.67 (d, 2C), 128.34 (s), 124.15 (t), 123.22 (s), 90.27 (s), 89.16
(s), 61.23 (t), 40.88 (t); MS (EI, 70 eV): m/z (%) ˆ 172 (100)
‡
(98)/250 (100) [M ], 206 (8), 171 (15), 153 (19), 128 (89), 95
(14), 77 (3); anal. calcd. for C12H11BrO: C 57.39, H 4.42, Br
31.82; found: C 58.07, H 4.17, Br 30.23.
‡
2-[2-(4-Bromophenylethynyl)oxiranyl]ethanol (4d)
[M ], 141 (70), 115 (46), 102 (17), 77 (17); anal. calcd. for
C12H12O: C 83.69, H 7.02; found: C 83.28, H 7.08.
The compound 4d was obtained using 3d (309 mg, 1.23 mmol)
and Na2HPO4 (436 mg, 3.07 mmol) in DCM (6 mL) and
mCPBA (425 mg, 2.46 mmol)as described for 4a. Column
chromatography (silica gel, 15% EtOAC-hexane) afforded 4d
as a yellow solid; yield: 53.6 mg (16%). IR (film): n ˆ 3370,
3060, 2912, 2852, 2190, 820 cmÀ1; 1H NMR (CDCl3, 500 MHz):
d ˆ 7.39 (d, J ˆ 8.4 Hz, 2H), 7.26 (m, J ˆ 8.4 Hz, 2H), 3.91 (m,
2H), 3.09 (d, J ˆ 5.4 Hz, 1H), 2.94 (d, J ˆ 5.4 Hz, 1H), 2.08 (m,
1H), 2.02 (m, 1H), 1.22 (br s, 1H, OH); 13C NMR (CDCl3,
125 MHz): d ˆ 133.62 (d, 2C), 131.95 (d, 2C), 123.53 (s), 121.09
(s), 88.48 (s), 82.85 (s), 59.75 (t), 54.75 (t), 49.90 (s), 38.96 (t);
2-(2-Phenylethynyloxiranyl)ethanol (4c)
The compound 4c was obtained using 3c (172 mg, 1.00 mmol)
and Na2HPO4 (350 mg, 2.46 mmol) in DCM (5 mL) and
mCPBA (362 mg, 2.10 mmol) as described for 4a. Column
chromatography (silica gel, 15% EtOAC-hexane) furnished 4c
as a colorless viscous liquid; yield: 58.4 mg (31%). IR (film):
n ˆ 3620 (OH), 3040, 2940, 2860, 2220, 1650, 1590 cmÀ1;
1H NMR (CDCl3, 500 MHz): d ˆ 7.39 (m, 2H), 7.28 (m, 3H),
3.92 (m, 2H), 3.10 (d, J ˆ 5.4 Hz, 1H), 2.93 (d, J ˆ 5.4 Hz, 1H),
2.15 (br s, 1H, OH), 2.11 (m, 1H), 2.01 (m, 1H); 13C NMR
(CDCl3, 125 MHz): d ˆ 132.18 (d), 129.14 (d, 2C), 128.69 (d,
2C), 122.05 (s), 87.17 (s), 83.96 (s), 59.79 (t), 54.81 (t), 49.99 (s),
‡
MS (EI, 70 eV): m/z (%) ˆ 268 (28)/266 (29) [M ], 238 (76), 236
(77), 207 (80), 205 (66), 182 (15), 157 (6), 129 (54), 126 (85), 73
‡
(100); HRMS (70 eV): calcd. for C12H1179BrO2 (M ): 265.9942;
‡
found: 265.9928/calcd. for C12H1181BrO2 (M ): 267.9922; found:
267.9908.
‡
39.05 (t); MS (EI, 70 eV): m/z (%) ˆ 188 (21) [M ], 172 (5), 145
(3), 127 (100), 102 (20), 77 (20); anal. calcd. for C12H12O2: C
76.57, H 6.43; found: C 76.02, H 6.32.
2-[5-(4-Bromophenyl)-furan-3-yl]ethanol (5d)
2-(5-Phenylfuran-3-yl)ethanol (5c)
A solution of AuCl3 in MeCN (54.1 mg; 5% w/w, 2.71 mg,
8.92 mmolAuCl 3) was added to a solution of 4d (32.1 mg,
120 mmol) in MeCN (0.5 mL) at 258C. After 27 h (the reaction
was monitored by thin layer chromatography) the solvent was
evaporated and residue was purified by column chromatog-
raphy (silica gel, 10% EtOAC-hexane). The pure compound 5d
was obtained as yellow solid; yield: 17.1 mg (53%). IR (film):
n ˆ 3411, 3061, 2924, 2854, 1584, 1265, 1067, 822 cmÀ1; 1H NMR
(CDCl3, 500 MHz): d ˆ 7.49 (m, 4H), 7.34 (s, 1H), 6.59 (s, 1H),
3.83 (t, J ˆ 6.3 Hz, 2H), 2.72 (t, J ˆ 6.3 Hz, 2H), 1.56 (brs, 1H,
OH); 13C NMR (CDCl3, 125 MHz): d ˆ 153.66 (s), 140.08 (d),
132.15 (d, 2C), 130.06 (s), 125.57 (d, 2C), 123.99 (s), 121.48 (s),
107.36 (d), 62.82 (t), 28.76 (t); MS (EI, 70 eV): m/z (%) ˆ 268
A solution of AuCl3 in MeCN (96.0 mg; 5% w/w, 4.80 mg,
15.8 mmolAuCl 3) was added to a solution of 4c (39.9 mg,
212 mmol) in MeCN (0.5 mL) at 258C. After 27 h (the reaction
was monitored by thin layer chromatography) the solvent was
evaporated and residue was purified by column chromatog-
raphy (silica gel, 8% EtOAC-hexane). Compound 5c was
obtained as a yellow viscous liquid; yield: 22.4 mg (56%). IR
1
(film): n ˆ 3383, 2925, 2885, 1617, 1580, 1123 cmÀ1; H NMR
(CDCl3, 500 MHz): d ˆ 7.52 (m, 2H), 7.26 (s, 1H), 7.24 (m, 2H),
7.14 (m, 1H), 6.48 (s, 1H), 3.72 (t, J ˆ 6.3 Hz, 2H), 2.61 (t, J ˆ
6.3 Hz, 1H), 1.57 (br s, 1H, OH); 13C NMR (CDCl3, 125 MHz):
d ˆ 154.76 (s), 139.76 (d), 131.14 (s), 129.01 (d, 2C), 127.74 (d),
124.07 (d, 2C), 123.73 (s), 106.73 (d), 62.85 (t), 28.83 (t); MS (EI,
‡
(99)/266 (28) [M ], 237 (24), 235 (24), 200 (13), 183 (33), 128
‡
‡
70 eV): m/z (%) ˆ 187 (49) [M ], 159 (9), 105 (100), 91 (5), 77
(83); HRMS (70 eV): calcd. for C12H1179BrO2 (M ): 265.9942;
‡
(32); anal. calcd. for C12H12O2: C 76.57, H 6.43; found: C 76.72,
H 6.07.
found: 265.9943/calcd. for C12H1181BrO2 (M ): 267.9922; found:
267.9922.
Adv. Synth. Catal. 2004, 346, 432 438
asc.wiley-vch.de
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
435

A. Stephen K. Hashmi, Pradipta Sinha
FULL PAPERS
22.17 (q), 20.89 (q), 16.49 (q), 14.89 (t); MS (EI, 70 eV): m/z
Pent-4-ynoic Acid 2-Isopropyl-5-methylcyclohexyl
Ester (2e)
‡
(%) ˆ 322 (3) [M ], 184 (4), 138 (5), 95 (5); anal. calcd. for
C19H30O4: C 70.77, H 9.38; found C 70.12, H 9.38.
To a solution of 4-pentynoic acid (491 mg, 5.00 mmol) in CCl4
(15 mL), l-menthol (859 mg, 5.50 mmol) and 4-toluenesulfon-
ic acid monohydrate (24.7 mg, 130 mmol) were added. The
reaction mixture was refluxed for 20 h. The reaction mixture
was cooled to room temperature and then diluted with ether.
The organic layer was washed with saturated NaHCO3, brine
and finally dried over anhydrous MgSO4. The solvent was
evaporated and column chromatography (silica gel, 1%
EtOAC-hexane) furnished 2e as a colorless viscous liquid;
yield: 1.01 g (85%). IR (film): n ˆ 3300, 2940, 2850, 2080, 1750,
1360 cmÀ1; 1H NMR (CDCl3, 500 MHz): d ˆ 4.70 (m, 1H), 2.52
(m, 4H), 1.99 (s, 1H), 1.96 (m, 1H), 1.87 (m, 1H), 1.69 (m, 2H),
1.58 (m, 1H), 1.49 (m, 1H), 1.47 (m, 1H), 0.98 (m, 2H), 0.89 (m,
6H), 0.76 (m, 3H); 13C NMR (CDCl3, 125 MHz): d ˆ 171.68 (s),
82.90 (s), 74.97 (d), 69.29 (d), 47.36 (d), 41.23 (t), 34.57 (t), 34.08
(t), 31.72 (d), 26.57 (d), 23.75 (t), 22.36 (q), 21.09 (q), 16.66 (q),
5-[2-(2-Hydroxyethyl)furan-2-yl]propionic Acid 2-
Isopropyl-5-methylcyclohexyl Ester (5e)
A solution of AuCl3 in MeCN (258 mg; 5% w/w, 12.9 mg,
42.5 mmolAuCl 3) was added to a solution of 4e (183 mg,
567 mmol) in MeCN (1 mL) at 258C. After 28 h (the reaction
was monitored by thin layer chromatography) the solvent was
evaporated and residue was purified by column chromatog-
raphy (silica gel, 18% EtOAC-hexane). Product 5e was
obtained as a yellow viscous liquid; yield: 46.3 mg (25%). IR
1
(film): n ˆ 3420, 2940, 2850, 1750, 1160, 1030 cmÀ1; H NMR
(CDCl3, 500 MHz): d ˆ 7.15 (s, 1H), 5.94 (s, 1H), 4.68 (m, 1H),
3.75 (t, J ˆ 6.35 Hz, 2H), 2.92 (t, J ˆ 7.6 Hz, 2H), 2.61 (m, 4H),
1.96 (m, 1H), 1.79 (m, 1H), 1.66 (m, 3H), 1.53 (br s, 1H), 1.46 (m,
1H), 1.35 (m, 1H), 1.24 (m, 1H), 1.03 (m, 1H), 0.87 (m, 6H), 0.73
(m, 3H); 13C NMR (CDCl3, 125 MHz): d ˆ 172.42 (s), 155.22
(s), 138.71 (d), 122.18 (s), 107.12 (d), 74.71 (d), 62.75 (t), 47.31
(d), 41.21 (t), 34.56 (t), 33.25 (t), 31.69 (d), 28.80 (t), 26.55 (d),
24.02 (t), 23.74 (t), 22.35 (q), 21.09 (q), 16.62 (q); MS (EI,
‡
14.87 (t); MS (CI): m/z (%) ˆ 237 (100) [M ], 221 (6), 138 (59),
95 (22), 81 (15); anal. calcd. for C15H24O2: C 76.23, H 10.24;
found: C 76.15, H 10.11.
‡
6-(2-Hydroxyethyl)hept-6-en-4-ynoic Acid 2-
Isopropyl-5-methylcyclohexyl Ester (3e)
70 eV): m/z (%) ˆ 322 (13) [M ], 184 (95), 138 (100), 95 (94);
analcalcd. for C 19H30O4: C 70.77, H 9.38; found: C 70.77, H 9.40.
The compound 3e was obtained using 1b (755 mg, 5.00 mmol)
and triethylamine (607 mg, 6.00 mmol) in THF (3 mL), CuI
(30.5 mg, 160 mmol), (PPh3)2PdCl2 (56.2 mg, 80.0 mmol) and 2e
(945 mg, 4.00 mmol) in THF (3 mL) as described for 3a.
Column chromatography (silica gel, 5% EtOAC-hexane)
furnished 3e as a colorless viscous liquid; yield: 1.32 mg
(86%). IR (film): n ˆ 3440, 3080, 2940, 2850, 2190, 1730 cmÀ1;
1H NMR (CDCl3, 500 MHz): d ˆ 5.35 (d, 1H), 5.26 (d, 1H),
4.70 (m, 1H), 3.77 (t, J ˆ 5.9 Hz, 2H), 2.62 (m, 2H), 2.53 (m,
2H), 2.37 (m, 2H), 1.97 (m, 1H), 1.86 (m, 1H), 1.66 (m, 2H), 1.62
(m, 2H), 1.48 (m, 1H), 1.37 (m, 1H), 1.04 (m, 2H), 0.89 (m, 6H),
0.76 (m, 3H); 13C NMR (CDCl3, 125 MHz): d ˆ 171.78 (s),
128.49 (s), 123.17 (t), 89.19 (d), 81.15 (s), 74.92 (d), 61.15 (t),
47.30 (d), 41.25 (t), 40.94 (t), 34.55 (t), 34.29 (t), 31.70 (d), 26.63
(d), 23.75 (t), 22.35 (q), 21.11 (q), 16.66 (q), 15.73 (t); MS (EI,
3-Methylenoct-4-yn-1-ol (3f)
The compound 3f was obtained using 1b (604 mg, 4.00 mmol)
and triethylamine (607 mg, 6.00 mmol) in THF (3 mL), CuI
(30.5 mg, 160 mmol), (PPh3)2PdCl2 (56.2 mg, 80.0 mmol) and 1-
pentyne (2f; 489 mg, 8.00 mmol) in THF (3 mL) as described
for 3a. Column chromatography (silica gel, 2% EtOAC-
hexane) afforded 3f as a yellow viscous liquid; yield: 226 mg
(41%). IR (film): n ˆ 3330, 3080, 2940, 2850, 2190, 1600 cmÀ1;
1H NMR (CDCl3, 500 MHz): d ˆ 5.34 (d, J ˆ 1.2 Hz, 1H), 5.24
(d, J ˆ 0.8 Hz, 1H), 3.79 (m, 2H), 2.39 (t, J ˆ 6.0 Hz, 2H), 2.28
(t, J ˆ 7.05 Hz, 2H), 1.66 (br s, 1H, OH), 1.54 (m, 2H), 0.99 (t,
J ˆ 7.45 Hz, 3H); 13C NMR (CDCl3, 125 MHz): d ˆ 128.79 (s),
122.58 (t), 91.38 (s), 80.64 (s), 62.25 (t), 41.13 (t), 22.45 (t), 21.56
‡
70 eV): m/z (%) ˆ 306 (2) [M ], 265 (28), 168 (41), 138 (100), 83
‡
(t), 13.83 (q); MS (EI, 70 eV): m/z (%) ˆ 138 (100) [M ], 109
(82); anal. calcd. for C19H30O3: C 74.47, H 9.87; found: C 74.33,
H 9.77.
(38), 95 (75), 81 (22); anal. calcd. for C9H14O: C 78.21, H 10.21;
found: C 77.85, H 10.43.
5-[2-(2-Hydroxyethyl)oxiranyl]-pent-4-ynoic Acid 2-
Isopropyl-5-methylcyclohexyl Ester (4e)
2-(2-Pent-1-ynyloxiranyl)ethanol (4f)
The compound 4e was obtained using 3e (306 mg, 1.00 mmol)
and Na2HPO4 (355 mg, 2.50 mmol) in DCM (5 mL) and
mCPBA (362 mg, 2.10 mmol) as described for 4a. Column
chromatography (silica gel, 12% EtOAC-hexane) furnished 4c
as a colorless viscous liquid; yield: 230 mg (71%). IR (film): n ˆ
3440, 3040, 2940, 2860, 2210, 1730, 1250 cmÀ1; 1H NMR
(CDCl3, 500 MHz): d ˆ 4.62 (m, 1H), 3.76 (m, 2H), 2.89 (d,
J ˆ 5.5 Hz, 1H), 2.76 (d, J ˆ 5.5 Hz, 1H), 2.51 (m, 1H, OH), 2.44
(m, 4H), 1.88 (m, 3H), 1.77 (m, 1H), 1.62 (m, 2H), 1.41 (m, 1H),
1.30 (m, 1H), 1.35 (m, 1H), 0.97 (m, 2H), 0.83 (m, 6H), 0.68 (m,
3H); 13C NMR (CDCl3, 125 MHz): d ˆ 171.39 (s), 82.79 (s),
79.04 (s), 74.82 (d), 59.45 (t), 54.39 (t), 49.47 (s), 47.09 (d), 41.04
(t), 39.09 (t), 34.35 (t), 33.73 (t), 31.52 (d), 26.47 (d), 23.58 (t),
The compound 4f was obtained using 3f (258 mg, 1.87 mmol)
and Na2HPO4 (664 mg, 4.68 mmol) in DCM (8 mL) and
mCPBA (678 mg, 3.93 mmol) as described for 4a. Column
chromatography (silica gel, 12% EtOAC-hexane) afforded 4f
as a yellow oil; yield: 170 mg (59%). IR (film): n ˆ 3400, 3040,
2940, 2860, 2205, 1250 cmÀ1; 1H NMR (CDCl3, 500 MHz): d ˆ
3.78 (m, 2H), 2.68 (d, J ˆ 5.4 Hz, 1H), 2.76 (d, J ˆ 5.4 Hz, 1H),
2.67 (br s, 1H, OH), 2.09 (t, J ˆ 7.05 Hz, 2H), 1.88 (m, 2H), 1.44
(m, 2H), 0.89 (t, J ˆ 7.3 Hz, 3H); 13C NMR (CDCl3, 125 MHz):
d ˆ 84.79 (s), 78.29 (s), 59.49 (t), 54.51 (t), 49.62 (s), 39.22 (t),
21.94 (t), 20.69 (t), 13.54 (q); MS (EI, 70 eV): m/z (%) ˆ 154 (2)
‡
[M ], 139 (4), 111 (14), 95 (65), 79 (199), 67 (36); anal. calcd. for
C9H14O2: C 70.10, H 9.15; found: C 70.40, H 9.05.
436
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2004, 346, 432 438

Transformation of Alkynyl Epoxides to Furans
FULL PAPERS
evaporated and residue was purified by column chromatog-
raphy (silica gel, 30% EtOAC-hexane). Compound 6 was
obtained as a yellow viscous liquid; yield: 30.7 mg (69%). IR
(film): n ˆ 3400, 2920, 2860, 2710, 2240, 1680, 1120, 1040 cmÀ1;
1H NMR (CDCl3, 500 MHz): d ˆ 9.85 (s, 1H), 7.95 (s, 1H), 6.41
(s, 1H), 3.69 (t, J ˆ 6.3 Hz, 2H), 2.76 (t, J ˆ 7.6 Hz, 2H), 1.90 (m,
2H), 1.88 (br s, 1H, OH); 13C NMR (CDCl3, 500 MHz): d ˆ
184.99 (d), 159.09 (s), 150.91 (d), 129.81 (s), 102.48 (d), 61.93 (t),
2-(5-Propylfuran-3-yl)ethanol (5f)
A solution of AuCl3 in MeCN (472 mg; 5% w/w, 23.6 mg,
77.8 mmolAuCl 3) was added to a solution of 4f (160 mg,
1.04 mmol) in MeCN (1 mL) at 258C. After 9 h (the reaction
was monitored by thin layer chromatography) the solvent was
evaporated and residue was purified by column chromatog-
raphy (silica gel, 8% EtOAC-hexane). The pure compound 5f
was obtained as a yellow viscous liquid; yield: 40.3 mg (25%).
IR (film): n ˆ 3411, 2964, 2871, 1613, 1256, 1053 cmÀ1; 1H NMR
(CDCl3, 500 MHz): d ˆ 7.15 (s, 1H), 5.91 (s, 1H), 3.76 (t, J ˆ
6.35 Hz, 2H), 2.63 (t, J ˆ 6.4 Hz, 2H), 2.55 (t, J ˆ 7.6 Hz, 2H),
1.64 (m, 2H), 1.62 (br s, 1H, OH), 0.95 (t, 3H); 13C NMR
(CDCl3, 125 MHz): d ˆ 154.44 (s), 138.25 (d), 122.01 (s), 106.54
(d), 62.78 (t), 30.44 (t), 28.84 (t), 21.61 (t), 14.09 (q); MS (EI,
‡
30.73 (t), 24.48 (t); MS (EI, 70 eV): m/z (%) ˆ 154 (49) [M ],
136 (100), 109 (60), 79 (22); HRMS (70 eV): calcd. for C8H10O3
‡
(M ): 154.0630; found: 154.0630.
Acknowledgements
‡
70 eV): m/z (%) ˆ 154 (56) [M ], 136 (2), 125 (100), 111 (5), 95
P. S. thanks the DAAD for a scholarship (A/02/29759). We also
are indebted to the Fonds der Chemischen Industrie and the
Karl-Ziegler Stiftung.
(9), 67 (12).
6-Diethoxymethylhept-6-en-4-yn-1-ol (3g)
The compound 3g was obtained using 2-bromo-3,3-diethox-
ypropene (1c; 2.09 g, 10.0 mmol) and triethylamine (911 mg,
9.00 mmol) in THF (4 mL), CuI (45.7 mg, 240 mmol),
(PPh3)2PdCl2 (84.2 mg, 120 mmol) and 2a (505 mg,
6.00 mmol) in THF (4 mL) as described for 3a. Column
chromatography (silica gel, 10% EtOAC-hexane) furnished
3g as a yellow viscous liquid; yield: 695 mg (55%). IR (film):
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n ˆ 3400, 3090, 2960, 2860, 2250, 1610, 1110 cmÀ1; H NMR
(CDCl3, 500 MHz): d ˆ 5.79 (s, 1H), 5.71 (s, 1H), 5.02 (s, 1H),
3.96 (t, J ˆ 5.8 Hz, 2H), 3.84 (m, 2H), 3.71 (m, 2H), 2.65 (t, J ˆ
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122.79 (t), 101.53 (d), 91.24 (s), 78.99 (s), 62.14 (t), 61.89 (t,
2C), 31.44 (t), 16.54 (t), 15.43 (q, 2C); MS (EI, 70 eV): m/z
‡
(%) ˆ 212 (2) [M ], 167 (8), 103 (100), 75 (60), 47 (57); anal.
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5-[(2-Diethoxymethyloxiranyl)]pent-4-yn-1-ol (4g)
The compound 4g was obtained using 3 g (425 mg, 2.00 mmol)
and Na2HPO4 (710 mg, 5.00 mmol) in DCM (8 mL) and
mCPBA (725 mg, 4.20 mmol) as described for 4a. Column
chromatography (silica gel, 18% EtOAC-hexane) furnished 4g
as a yellow oil; yield: 139 mg (30%). IR (film): n ˆ 3420, 3050,
2960, 2860, 2220, 1100, 900 cmÀ1; 1H NMR (CDCl3, 500 MHz):
d ˆ 4.36 (s, 1H), 3.68 (m, 4H), 3.55 (m, 2H), 2.96 (d, J ˆ 5.8 Hz,
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(t), 61.57 (t), 51.62 (s), 51.18 (t), 31.11 (t), 15.73 (t), 15.37 (q),
‡
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(6), 103 (100), 75 (27), 47 (26); anal. calcd. for C12H20O4: C
63.14, H 8.83; found: C 63.11, H 8.65.
5-(3-Hydroxypropyl)furan-2-carbaldehyde (6)
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14.5 mmolAuCl 3) was added to a solution of 4g (66.2 mg,
290 mmol) in MeCN (0.5 mL) at 258C. After 1 h (the reaction
was monitored by thin layer chromatography) the solvent was
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¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
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