Facile synthesis of α,β-acetylenic ketones and 2,5-disubstituted furans: Consecutive activation of triple and double bond with ZnBr2 toward the synthesis of furan ring

Article abstract of DOI:10.1016/j.tet.2005.06.104

α,β-Acetylenic ketones were synthesized from the reaction of acid chlorides and acetylenic compounds in the presence of ZnBr2 and DIEA in acetonitrile. From the acetylenic ketones having nearby methylene unit, 2,5-disubstituted furan derivatives could be synthesized under the same reaction conditions.

Full text of DOI:10.1016/j.tet.2005.06.104

Tetrahedron 61 (2005) 8705–8710
Facile synthesis of a,b-acetylenic ketones and 2,5-disubstituted
furans: consecutive activation of triple and double bond with
ZnBr2 toward the synthesis of furan ring
*
Ka Young Lee, Mi Jung Lee and Jae Nyoung Kim
Department of Chemistry and Institute of Basic Science, Chonnam National University, Gwangju 500-757, South Korea
Received 1 June 2005; accepted 24 June 2005
Available online 18 July 2005
Abstract—a,b-Acetylenic ketones were synthesized from the reaction of acid chlorides and acetylenic compounds in the presence of ZnBr2
and DIEA in acetonitrile. From the acetylenic ketones having nearby methylene unit, 2,5-disubstituted furan derivatives could be synthesized
under the same reaction conditions.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
intermediates3 and numerous synthetic methods have been
reported.3,4 Among them the use of copper(I) salt in
combination of a tertiary amine is widely used.4 However,
the method used carcinogenic triethylamine as the solvent
and required long time (30 h) for the reaction.4a,b Very
recently, the combination of palladium catalyst and CuI has
been published.4d,e However, most of the reported methods
have some problems such as low yields, use of toxic or
expensive reagents, and long reaction time. Moreover, to the
best of our knowledge, the use of zinc triflate and amine
system of Carreira2 has not been reported for the synthesis
of a,b-acetylenic ketones. In searching for the usefulness of
our reaction conditions,1 we envisioned that the reaction of
aryl acetylene 1 and acid chloride 2 under the conditions
could afford valuable a,b-acetylenic ketones 3 (Scheme 2).
Recently, we reported the alkynylation of N-tosylimines1a
and quinolinium salts1b with aryl acetylenes promoted by
ZnBr2 and N,N-diisopropylethylamine (DIEA, Hunig base)
in acetonitrile. In the reactions, we obtained N-tosyl
propargylamines1a and 1-acyl-1,2-dihydroquinolines1b in
moderate to good yields by the addition of in situ generated
zinc acetylide (Scheme 1). On the other hand, Carreira and
co-workers have reported a mild procedure for the addition
of acetylenic compounds to nitrones,2a N-acyliminium
salts,2b and aldehydes2c involving the in situ generated
zinc acetylide in the presence of zinc triflate and tertiary
amine. The two procedures were similar conceptually,
however, the latter procedure used hygroscopic and
expensive zinc triflate instead of ZnBr2.
As expected the reaction of phenylacetylene (1a) and
benzoyl chloride (2a) in acetonitrile in the presence of
a,b-Acetylenic ketones are very important synthetic
Scheme 1.
Keywords: Acetylenic ketones; Phenylacetylene; Furans.
*
Corresponding author. Tel.: C82 62 530 3381; fax: C82 62 530 3389; e-mail: kimjn@chonnam.ac.kr
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.06.104

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K. Y. Lee et al. / Tetrahedron 61 (2005) 8705–8710
Scheme 2.
ZnBr2 and DIEA gave the desired compound 3a in high
yield (82%). The yield was satisfactory and the reaction
conditions were very convenient to carry out in a practical
sense. Encouraged by the results we examined the reactions
between 1a–d and 2a–e and the results are summarized in
Table 1. As shown, substituted benzoyl chlorides (entries 2
and 3) and pivaloyl chloride (entry 4) could be used as the
electrophilic components. The reaction with benzoic
Table 1. Synthesis of a,b-acetylenic ketonesa,b
Entry
1
Acetylenes
Acid chlorides
Products (%)
3a (82)3g
3b (85)4e
3c (82)3g
2a
1a
1a
2
3
4
5
2b
2c
1a
1a
2d
2a
3d (94)3g
1b
3e (84)4e
6
2a
2a
1c
1d
1a
3f (81)4e
7
8
3g (72)8a
2e
4(77)5
3h (16%)8b
a Conditions: acetylenic compound 1 (1 equiv), acid chloride 2 (1.2 equiv), ZnBr2 (1.2 equiv), DIEA (1.2 equiv), rt, 90 min, CH3CN.
b The reaction of 1a and 2a in the presence of Zn(OTf)2 (1.2 equiv) and DIEA (rt, 90 min) gave 3a in a similar yield (80%). The use of ZnCl2, Znl2, or catalytic
amounts of ZnBr2 did not give 3a in appreciable yield.

K. Y. Lee et al. / Tetrahedron 61 (2005) 8705–8710
8707
Scheme 3.
Table 2. Synthesis of 2,5-disubstituted furansa
Entry
1
Acetylenes
Acid chlorides
Time (h)
2
Products (%)
2a
2b
1e
1e
5a (64)
2
3
3
3
5b (70)
5c (33)
1e
2d
3i (59)
5d (67)
4
5
2a
2a
3
8
1f
1g
5e (66)
6b
2a
20
1h
5f (70)
a Conditions: acetylenic compound 1 (1 equiv), acid chloride 2 (1.2 equiv), ZnBr2 (1.2 equiv), DIEA (1.2 equiv), rt, times given in that table.
b Conditions: 2a (2 equiv), ZnBr2 (2 equiv). DIEA (2 equiv), rt, 20 h.

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K. Y. Lee et al. / Tetrahedron 61 (2005) 8705–8710
anhydride instead of benzoyl chloride failed. The acid
chloride bearing a-proton showed different reactivity under
the reaction conditions. As an example (entry 8), for the
reaction of propionyl chloride (2e) and phenylacetylene we
obtained the desired acetylenic ketone 3h in low yield
(16%) together with ketene dimer derivative 4 as the major
product (77%).5
Although, the convertibility of acetylenic ketone into furan
was known,7 our findings suggest many important scientific
issues: (1) furan could be synthesized in a one-pot from
benzoyl chlorides and phenyl propargyl ethers in short time
in high yield and (2) ZnBr2 could act well for the acetylene–
allene isomerization and concomitant activation of the
allene moiety toward cyclization. In other words, triple bond
of acetylenic compound was activated by ZnBr2 to generate
efficiently the corresponding zinc acetylide species.1a After
the formation of a,b-acetylenic ketones ZnBr2 played the
role of activation of triple bond once more to be isomerized
into the corresponding allenic ketone derivatives. Finally,
during the formation of furan skeleton ZnBr2 activates the
double bond of allene moiety to facilitate the formation of
furan ring. The results for the synthesis of furans are
illustrated in Table 2. For the reaction of 1e and 2d (entry 3)
the yield of 5c was low. Instead acetylenic ketone 3i was
isolated as the major product. During the cyclization stage
for furan the bulky tert-butyl group might affect. For the
reaction of 1h (entry 6), long reaction time was required in
order to obtain moderate yield of 5f.
Aryl acetylenes 1a–c gave the desired a,b-acetylenic
ketones in good to excellent yields. However, the situations
were different for the alkyl group-attached alkynes (vide
infra). In our previous synthesis of N-tosylpropargylamines,
alkyl group-substituted acetylenic compounds failed com-
pletely presumably due to the low acidity of the acetylenic
hydrogen and the low electrophilicity of N-tosylimine.1a
However, the reaction of benzoyl chloride and 1-decyne
(1d) gave the desired a,b-acetylenic ketone 3g in moderate
yield.
Moreover, very interesting results were observed when we
used aryl propargyl ethers 1e–g or N-propargylphthalimide
(1h) in the same reaction. 5-Phenyl-2-phenoxyfuran (5a)
was obtained in 64% yield in a one-pot reaction from the
reaction of 1e and 2a.6,7 This compound was generated
definitively from the corresponding a,b-acetylenic ketone
intermediate with ZnBr2 assistance. The plausible reaction
mechanism is suggested in Scheme 3 (vide infra). The
ZnBr2-catalyzed and base-assisted propargyl-allenyl iso-
merization occurred to allene derivative (II), which
immediately undergoes sequential transformation into
furans as reported in a similar system.6a,d,7 At this stage,
we could not rule out the possibility of involvement of
moisture in the reaction. Synthesis of furan derivatives from
acetylenic ketones or allenic ketones has been accomplished
with the aid of CuI/Et3N or AuCl3.7 In our reaction, ZnBr2
played the same role of CuI or AuCl3 without any problems.
The formation of furan derivatives occurs definitively from
the corresponding a,b-acetylenic ketones (vide supra).
When we carried out the reaction of 1d and 2a at rt we
obtained only 3g. The reaction of 3g under the same
conditions at elevated temperature afforded 5g in 61% yield.
The reaction of 1d and 2a at elevated temperature gave 5g
directly (Scheme 4) in 60% yield. We obtained same results
from the reaction of 1i and 2a. From the experiments, we
could conclude that the furan compounds 5a–h were formed
via the intermediacy a,b-acetylenic ketone compounds.
In conclusion, we found that zinc acetylide species can react
with acyl chlorides to give a,b-acetylenic ketone derivatives
in high yields in short time. The zinc acetylides can be
Scheme 4.

K. Y. Lee et al. / Tetrahedron 61 (2005) 8705–8710
8709
generated efficiently from the corresponding acetylenic
compounds with the aid of ZnBr2 and DIEA in acetonitrile.
For the acetylenic ketones bearing nearby methylene unit,
concomitant isomerization to allene and ZnBr2-assisted
cyclization occurred to afford 2,5-disubstituted furan
derivatives.
C19H19NO3S: C, 66.84; H, 5.61; N, 4.10. Found: C, 66.95;
H, 5.59, N, 4.00.
2.3. Typical procedure for the synthesis of 5a
To a stirred solution of benzoyl chloride (2a, 169 mg,
1.2 mmol) in CH3CN (3 mL) was added phenyl propargyl
ether (1e, 132 mg, 1.0 mmol), ZnBr2 (270 mg, 1.2 mmol),
and N,N-diisopropylethylamine (DIEA, 155 mg, 1.2 mmol).
The reaction mixture was stirred for 2 h at rt. After the usual
aqueous workup and column chromatographic purification
process (hexanes/ether, 10:1) we obtained 5a, 152 mg
(64%). The spectroscopic data of the prepared furans 5a–h
are as follows.
2. Experimental
2.1. General procedure
1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were
recorded in CDCl3. The signal positions are reported in ppm
relative to TMS (d scale) used as an internal standard. The
separations were carried out by flash column chromato-
graphy over silica gel (230–400 mesh ASTM). Organic
extracts were dried over anhydrous MgSO4 and the solvents
were evaporated on a rotary evaporator under water
aspirator pressure. IR spectra are reported in cmK1. Mass
spectra were obtained from the Korea Basic Science
Institute (Gwangju branch). Melting points are uncorrected.
The combustion analyzes were carried out at Korea
Research Institute of Chemical Technology, Taejon,
Korea. The starting materials 1a–d were obtained from
commercial sources. Compounds 1e–h were prepared from
phenol, 2-naphthol, 1,4-dihydroxybenzene, and phthalimide
with propargyl bromide in the presence of K2CO3 in DMF.
Identification of starting materials 1e–h was carried out with
2.3.1. Compound 5a. White solid (64%), mp 66–67 8C; IR
(KBr) 1547, 1485, 1242 cmK1 1H NMR (300 MHz,
;
CDCl3) d 5.63 (d, JZ3.3 Hz, 1H), 6.57 (d, JZ3.3 Hz,
1H), 7.08–7.22 (m, 4H), 7.29–7.35 (m, 4H), 7.56–7.58 (m,
2H); 13C NMR (75 MHz, CDCl3) d 91.26, 106.09, 116.93,
122.97, 123.90, 126.89, 128.62, 129.69, 130.49, 146.28,
156.04, 156.85; ESIMS m/z 237 (MCCH). Anal. Calcd for
C16H12O2: C, 81.34; H, 5.12. Found: C, 81.28; H, 5.17.
2.3.2. Compound 5b. White solid (70%), mp 46–47 8C; IR
(KBr) 1554, 1489, 1250 cmK1 1H NMR (300 MHz,
;
CDCl3) d 2.19 (s, 3H), 5.50 (d, JZ3.3 Hz, 1H), 6.38 (d,
JZ3.3 Hz, 1H), 6.94–7.02 (m, 5H), 7.14–7.22 (m, 2H),
7.33–7.36 (m, 2H); 13C NMR (75 MHz, CDCl3) d 21.14,
91.23, 105.24, 116.82, 122.96, 123.78, 127.82, 129.28,
129.65, 136.66, 146.55, 155.64, 156.94. Anal. Calcd for
C17H14O2: C, 81.58; H, 5.64. Found: C, 81.50; H, 5.59.
1
their H and/or 13C NMR spectra simply.
2.2. Typical procedure for the synthesis of 3a
2.3.3. Compound 5c. Oil (33%); IR (KBr) 2966, 1566,
1
1489, 1250 cmK1; H NMR (300 MHz, CDCl3) d 1.26 (s,
To a stirred solution of benzoyl chloride (2a, 169 mg,
1.2 mmol) in CH3CN (3 mL) was added phenylacetylene
(1a, 102 mg, 1.0 mmol), ZnBr2 (270 mg, 1.2 mmol), and
N,N-diisopropylethylamine (DIEA, 155 mg, 1.2 mmol).
The reaction mixture was stirred for 90 min at rt. After the
usual aqueous workup and column chromatographic puri-
fication process (hexanes/ether, 10:1) we obtained 3a,
169 mg (82%). Identification of prepared compounds 3a–h
9H), 5.44 (d, JZ3.3 Hz, 1H), 5.89 (d, JZ3.3 Hz, 1H), 6.98–
7.11 (m, 3H), 7.28–7.35 (m, 2H); 13C NMR (75 MHz,
CDCl3) d 28.83, 32.50, 89.32, 102.58, 116.46, 123.37,
129.57, 154.27, 156.62, 157.38. Anal. Calcd for C14H16O2:
C, 77.75; H, 7.46. Found: C, 77.45; H, 7.38.
2.3.4. Compound 5d. White solid (67%), mp 109–110 8C;
IR (KBr) 1547, 1250 cmK1; 1H NMR (300 MHz, CDCl3) d
5.72 (d, JZ3.3 Hz, 1H), 6.64 (d, JZ3.3 Hz, 1H), 7.19–7.24
(m, 1H), 7.31–7.49 (m, 6H), 7.58–7.62 (m, 2H), 7.72–7.85
(m, 3H); 13C NMR (75 MHz, CDCl3) d 91.49, 106.16,
112.42, 118.02, 123.02, 125.02, 126.73, 126.95, 127.29,
127.75, 128.66, 129.92, 130.48, 130.50, 134.02, 146.42,
154.60, 156.06. Anal. Calcd for C20H14O2: C, 83.90; H,
4.93. Found: C, 83.95; H, 4.92.
1
and 4 was carried out with their melting points, H and/or
13C NMR spectra simply in comparison with the reported
data (3a,3g 3b,4e 3c,3g 3d,3g 3e,4e 3f,4e 3g,8a 3h,8b and 45).
Spectroscopic data of compounds 3i and 3j are as follows.
2.2.1. Compound 3i. Oil (59%); IR (KBr) 2970, 2214,
1
1674, 1493 cmK1; H NMR (300 MHz, CDCl3) d 1.13 (s,
9H), 4.87 (s, 2H), 6.95–7.04 (m, 3H), 7.28–7.34 (m, 2H);
13C NMR (75 MHz, CDCl3) d 25.70, 44.69, 55.68, 83.97,
87.77, 115.05, 121.94, 129.53, 157.22, 193.36; ESIMS m/z
217 (MCCH). Anal. Calcd for C14H16O2: C, 77.75; H, 7.46.
Found: C, 77.92; H, 7.59.
2.3.5. Compound 5e. White solid (66%), mp 129–130 8C;
IR (KBr) 1493, 1176 cmK1; 1H NMR (300 MHz, CDCl3) d
5.63 (d, JZ3.3 Hz, 2H), 6.60 (d, JZ3.3 Hz, 2H), 7.10 (s,
4H), 7.20–7.25 (m, 2H), 7.33–7.38 (m, 4H), 7.57–7.60 (m,
4H); 13C NMR (75 MHz, CDCl3) d 89.81, 105.10, 117.37,
121.97, 125.95, 127.65, 129.43, 145.26, 151.87, 155.35;
ESIMS m/z 395 (MCCH). Anal. Calcd for C26H18O4: C,
79.17; H, 4.60. Found: C, 79.34; H, 4.72.
2.2.2. Compound 3j. Oil (54%); IR (KBr) 2229, 1647,
1
1346, 1265, 1161 cmK1; H NMR (300 MHz, CDCl3) d
1.25 (t, JZ7.2 Hz, 3H), 2.21 (s, 3H), 3.38 (q, JZ7.2 Hz,
2H), 4.44 (s, 2H), 7.18–7.22 (m, 2H), 7.37–7.46 (m, 2H),
7.57–7.64 (m, 1H), 7.73–7.84 (m, 4H); 13C NMR (75 MHz,
CDCl3) d 13.21, 21.29, 36.05, 41.79, 83.06, 86.99, 127.54,
128.49, 129.31, 129.69, 134.25, 135.41, 135.94, 143.90,
176.77; ESIMS m/z 342 (MCCH). Anal. Calcd for
2.3.6. Compound 5f. White solid (70%), mp 161–162 8C;
IR (KBr) 1736, 1369 cmK1; 1H NMR (300 MHz, CDCl3) d
6.53 (d, JZ3.3 Hz, 1H), 6.77 (d, JZ3.3 Hz, 1H), 7.24–7.30

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K. Y. Lee et al. / Tetrahedron 61 (2005) 8705–8710
(b) Marko, I. F.; Southern, J. M. J. Org. Chem. 1990, 55, 3368.
(c) Vasilyev, A. V.; Walspurger, S.; Pale, P.; Sommer, J.
Tetrahedron Lett. 2004, 45, 3379. (d) Rossi, E.; Abbiati, G.;
Canevari, V.; Nava, D.; Arcadi, A. Tetrahedron 2004, 60,
11391. (e) Jeevanandam, A.; Narkunan, K.; Ling, Y.-C. J. Org.
Chem. 2001, 66, 6014. (f) Maeda, Y.; Kakiuchi, N.; Matsumura,
S.; Nishimura, T.; Kawamura, T.; Uemura, S. J. Org. Chem.
2002, 67, 6718. (g) Alonso, D. A.; Najera, C.; Pacheco, M. C.
J. Org. Chem. 2004, 69, 1615 and further references cited
therein.
(m, 1H), 7.34–7.40 (m, 2H), 7.64–7.68 (m, 2H), 7.80–7.83
(m, 2H), 7.95–7.98 (m, 2H); 13C NMR (75 MHz, CDCl3) d
106.28, 108.74, 123.89, 124.11, 127.80, 128.62, 130.06,
131.57, 134.76, 137.03, 152.92, 166.09; ESIMS m/z 290
(MCCH). Anal. Calcd for C18H11NO3: C, 74.73; H, 3.83;
N, 4.84. Found: C, 74.75; H, 3.95; N, 4.89.
2.3.7. Compound 5g. Oil (60%); IR (KBr) 2927, 1546,
1
1461 cmK1; H NMR (300 MHz, CDCl3) d 0.89 (t, JZ
6.9 Hz, 3H), 1.25–1.40 (m, 8H), 1.64–1.74 (m, 2H), 2.68 (t,
JZ7.5 Hz, 2H), 6.06 (d, JZ3.3 Hz, 1H), 6.55 (d, JZ
3.3 Hz, 1H), 7.18–7.26 (m, 1H), 7.33–7.38 (m, 2H), 7.62–
7.65 (m, 2H); 13C NMR (75 MHz, CDCl3) d 14.15, 22.70,
28.13, 28.22, 29.09, 29.21, 31.82, 105.64, 106.82, 123.31,
126.71, 128.60, 131.27, 152.07, 156.52. Anal. Calcd for
C17H22O: C, 84.25; H, 9.15. Found: C, 83.99; H, 9.21.
4. For the synthesis of a,b-acetylenic ketones involving the use of
CuI, see: (a) Chowdhury, C.; Kundu, N. G. Tetrahedron Lett.
1996, 37, 7323. (b) Chowdhury, C.; Kundu, N. G. Tetrahedron
1999, 55, 7011. (c) Wang, J.-X.; Wei, B.; Hu, Y.; Liu, Z.; Fu, Y.
Synth. Commun. 2001, 31, 3527. (d) Cox, R. J.; Ritson, D. J.;
Dane, T. A.; Berge, J.; Charmant, J. P. H.; Kantacha, A. Chem.
Commun. 2005, 1037. (e) Chen, L.; Li, C.-J. Org. Lett. 2004, 6,
3151. (f) Guo, M.; Li, D.; Zhang, Z. J. Org. Chem. 2003, 68,
10172. (g) Tohda, Y.; Sonogashira, K.; Hagihara, N. Synthesis
1977, 777.
2.3.8. Compound 5h. White solid (56%), mp 140–150 8C
(dec); IR (KBr) 1681, 1354, 1169 cmK1 1H NMR
;
(300 MHz, CDCl3) d 1.56 (t, JZ7.2 Hz, 3H), 2.44 (s, 3H),
3.59 (q, JZ7.2 Hz, 2H), 6.30 (d, JZ3.3 Hz, 1H), 6.62 (d,
JZ3.3 Hz, 1H), 7.26–7.38 (m, 5H), 7.46–7.50 (m, 2H),
7.67–7.71 (m, 2H); 13C NMR (75 MHz, CDCl3) d 12.94,
20.54, 44.28, 105.02, 108.57, 122.56, 126.60, 126.76,
127.62, 128.50, 129.27, 134.96, 142.77, 143.42, 150.54;
ESIMS m/z 342 (MCCH). Anal. Calcd for C19H19NO3S: C,
66.84; H, 5.61; N, 4.10. Found: C, 66.81; H, 5.85; N, 4.33.
5. For the generation and dimerization of ketene species from
propionyl chloride, please see: Farnum, D. G.; Johnson, J. R.;
Hess, R. E.; Marshall, T. B.; Webster, B. J. Am. Chem. Soc.
1965, 87, 5191.
6. For the synthesis and biological importance of 2,5-disubstituted
furan derivatives, see: (a) Marshall, J. A.; Van Devender, E. A.
J. Org. Chem. 2001, 66, 8037. (b) Padwa, A.; Rashatasakhon,
P.; Rose, M. J. Org. Chem. 2003, 68, 5139. (c) Pohmakotr, M.;
Takampon, A.; Ratchataphusit, J. Tetrahedron 1996, 52, 7149.
(d) Takai, K.; Morita, R.; Sakamoto, S. Synlett 2001, 1614. (e)
Kolasa, T.; Stewart, A. O.; Brooks, C. D. W. Tetrahedron:
Asymmetry 1996, 7, 729. (f) Stoner, E. J.; Roden, B. A.;
Chemburkar, S. Tetrahedron Lett. 1997, 38, 4981. (g) Dickman,
D. A.; Ku, Y.-Y.; Morton, H. E.; Chemburkar, S. R.; Patel, H.
H.; Thomas, A.; Plata, D. J.; Sawick, D. P. Tetrahedron:
Assymmetry 1997, 8, 1791.
Acknowledgements
This work was supported by Korea Research Foundation
Grant (KRF-2002-015-CP0215). Spectroscopic data was
obtained from the Korea Basic Science Institute, Gwangju
branch.
7. For the synthesis of furan derivatives by cycloisomerization of
alkyne- and allene-containing compounds, see: (a) Patil, N. T.;
Wu, H.; Yamamoto, Y. J. Org. Chem. 2005, 70, 4531. (b)
Sniady, A.; Wheeler, K. A.; Dembinski, R. Org. Lett. 2005, 7,
1769. (c) Brown, R. C. D. Angew. Chem., Int. Ed. 2005, 44, 850.
(d) Hoffmann-Roder, A.; Krause, N. Org. Biomol. Chem. 2005,
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References and notes
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