Efficient solvent-free synthesis of tertiary propargylic alcohols from arylacetylenes and ketones promoted by tert-BuOK

Article abstract of DOI:10.1007/s11164-012-0765-9

A mild and efficient method for the alkynylation of arylacetylenes with ketones promoted by tert-BuOK under solvent-free conditions was developed. The present green synthesis was applicable to many kinds of aromatic and aliphatic ketones providing good to excellent yields of tertiary propargylic alcohols. Graphical abstract: A mild and efficient method for the alkynylation of arylacetylenes with ketones promoted by tert-BuOK under solvent-free conditions was developed. The present green synthesis was applicable to many kinds of aromatic and aliphatic ketones providing good to excellent yields of tertiary propargylic alcohols.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s11164-012-0765-9

Res Chem Intermed (2013) 39:2391–2399
DOI 10.1007/s11164-012-0765-9
Efficient solvent-free synthesis of tertiary propargylic
alcohols from arylacetylenes and ketones promoted
by tert-BuOK
•
•
•
Shufeng Chen Fang Yuan Haiying Zhao
Baoguo Li
Received: 15 June 2012 / Accepted: 7 August 2012 / Published online: 25 August 2012
Ó Springer Science+Business Media B.V. 2012
Abstract A mild and efficient method for the alkynylation of arylacetylenes with
ketones promoted by tert-BuOK under solvent-free conditions was developed. The
present green synthesis was applicable to many kinds of aromatic and aliphatic ketones
providing good to excellent yields of tertiary propargylic alcohols.
Keywords Solvent-free Á Tertiary propargylic alcohols Á Alkynylation Á
Potassium tert-butoxide
Introduction
Sustainable development has become one of the fundamental demands in both
academic and industrial research [1–3]. Solvent-free organic reactions have been
receiving more attention for many years because of their clean and environment-
friendly protocols as well as convenient means of product purification [4–12]. It
becomes more and more urgent for organic chemists to develop benign syntheses
that save resources and energy and also minimize the waste. A generally desirable
process is the uncatalysed transformation of neat reactants under mild reaction
conditions due to their simplicity and cost efficiency.
On the other hand, the alkynylation reaction of carbonyl compounds that
generates propargylic alcohols is one of the most useful carbon–carbon bond-
forming reactions (for a review, see [13]). Moreover, the corresponding propargylic
alcohols are important intermediates and versatile building blocks for the synthesis
of fine chemicals, natural products and pharmaceuticals [14–18]. Over the past
decades, enormous efforts have been devoted to the development of highly efficient
propargylic alcohol synthesis. Among which the nucleophilic addition reactions of
S. Chen Á F. Yuan Á H. Zhao Á B. Li (&)
College of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot 010021, China
e-mail: baoguol@sohu.com
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S. Chen et al.
acetylide anions, which are generated in situ from stoichiometric or excess amounts
of organometallic bases, to carbonyl compounds are widely used in the synthesis of
these substances [19–29]. These organometallic reagents are air- and water-sensitive
and thus turn out to be disadvantageous. Another practical manner is catalytic
metal-free technology for the direct alkynylation of terminal alkynes to carbonyl
compounds [30–34]. Apart from these methods, solvent-free alkynylation reactions
have been proved to be suitable for the propargylic alcohol synthesis. For example,
Miyamoto and co-workers [35] reported an addition reaction of phenylacetylene to
aliphatic ketones promoted by stoichiometric tert-BuOK with moderate yields under
ball-milling condition. Unfortunately, this strategy is not efficient for alkynylating
aromatic ketones with terminal alkynes. In 2008, Wang and co-workers [36]
disclosed a solvent-free method for the preparation of tertiary propargylic alcohols
from aromatic ketones with terminal alkynes that rely on the use of 18-crown-6 and
ball-milling condition with solid KOH as the base. However, poisonous 18-crown-6
is crucial for this transformation.
During the preparation of this manuscript, Song and co-workers [37] reported a
transition-metal-free method for performing alkynylation reactions of various
ketones with terminal alkynes that rely on the use of catalytic amount of
tetrabutylammonium chloride as a promoter and solid KOH as a base in THF.
However, the efficiency of this technique is not satisfactory, because an excess of
alkynes (4 equivalent) and the long reaction time (several days) are necessary in
order to promote complete reactions. Considering the important applications of
propargylic alcohols, further development of more efficient and environment-
friendly methodologies for these compounds is highly desirable. Here, we wish to
report an efficient and mild method for the preparation of tertiary propargylic
alcohols based on the alkynylation reaction of arylacetylenes with ketones promoted
by tert-BuOK under solvent-free conditions (Scheme 1).
Results and discussion
Firstly, we employed phenylacetylene 1a and acetophenone 2a as the substrates to
investigate this solvent-free alkynylation reaction. The effectiveness of various
bases was carefully examined for this process. The results are summarized in
Table 1. tert-BuOK was found to be the most suitable base for this transformation
giving the corresponding tertiary propargylic alcohol 3a in 81 % yield at room
temperature in 0.5 h (Table 1, entry 1), whereas only a trace of 3a was detected
when KOH was used under the same reaction conditions (Table 1, entry 2). Other
O
OH
tert-BuOK
+
Ph
Me
neat, r.t.
3a
1a
2a
Scheme 1 Synthesis of tertiary propargylic alcohol under solvent-free conditions
123

Efficient solvent-free synthesis of tertiary propargylic alcohols
2393
bases, such as K2CO3 and KOAc, could not afford the alkynylated product (Table 1,
entries 3 and 4). Moreover, no propargylic alcohol 3a product was observed when
the reaction was carried out with organic bases, such as Et3N and DBU (Table 1,
entries 5 and 6). For comparison, other strong bases were also screened, and none
could afford the alkynylation product 3a (Table 1, entries 7–9). Therefore, tert-
BuOK was identified as the most efficient base in this alkynylation reaction under
solvent-free conditions at ambient temperature.
With the optimized reaction conditions to hand, the scope of this alkynylation
reaction was investigated by using phenylacetylene and a variety of aromatic as well as
aliphatic ketones as the substrates (Table 2). Various substitutions on the aromatic ring
could betolerated, andthe reactiongavemoderate togoodisolatedyieldsoftheproducts
3a–j. Various substitutions on the phenyl ring could be tolerated, and the reaction gave
moderate to good yields of the products 3a–f (Table 2, entries 1–6). It was found that
substrates with phenyl ring bearing halogen group generally gave satisfactory yields
(Table 2, entries 2–4). On the other hand, the reaction with p-MeO substituted substrate
could only afford the corresponding propargylic alcohol product in moderate yield,
which revealed that the reaction was slightly affected by the electronic effect (entry 6).
Interestingly, it was found that the aromatic ketones with larger steric hindrance, such as
benzophenone and 9-fluorenone, were also suitable for this solvent-free reaction and
gave excellent product yields (Table 2, entries 7 and 8). Moreover, the result showed
that this approach was also applicable to the substrates bearing heteroaromatic ring
substituents to give the alkynylation products in moderate yields (Table 2, entries 9 and
10). Besides, when aliphatic ketones were applied to this transformation, the alkyl-
substituted tertiary propargylic alcohols were successfully obtained, albeit with slightly
low yields (Table 2, entries 11–13).
Table 1 Effect of the base on the alkynylation reaction of phenylacetylene (1a) with acetophenone (2a)
under solvent-free conditions
OH
O
base, neat
+
r.t.
3a
1a
2a
Entry
Base
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
9
tert-BuOK
KOH
0.5
2
81
Trace
K2CO3
KOAc
Et3N
2
0
0
0
0
0
0
0
2
2
DBU
1
MeONa
EtONa
NH2Na
3
3
3
Reactions were carried out with 0.75 mmol of 1a, 0.5 mmol of 2a, and 0.5 mmol of tert-BuOK
a
Yield of isolated product after chromatography
123

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S. Chen et al.
Next, we examined the scope of the terminal alkynes, as shown in Table 3. It was
found that substrates with a phenyl ring bearing halogen group generally gave high
yields of the addition products (Table 3, entries 1 and 2), while substrates with
electron-donating substituent on the phenyl ring, such as p-CH3 and p-CH3O, only
afforded moderate yields of corresponding propargylic alcohol products (Table 3,
entries 3 and 4). These results indicated that the reaction was significantly affected
by the electronic effect of the aromatic alkynes.
Finally, considering the general applications of this solvent-free alkynylation
reaction, we demonstrated the gram-scale progress, and three examples of large-
scale reactions with satisfactory yields of the products were shown in Scheme 2.
Table 2 tert-BuOK promoted alkynylation reactions of phenylacetylene (1a) with various ketones
O
OH
R2
tert-BuOK
+
R1
R2
neat, r.t.
R1
2a-m
1a
3a-m
Reaction time (h)
Entry
2, R1, R2
3, Yield (%)a
1
2
3
4
5
6
7
8
2a, Ph, CH3
0.5
0.5
0.5
0.5
0.5
0.5
2
3a, 81
3b, 83
3c, 87
3d, 69
3e, 85
3f, 61
3g, 75
3h, 82
2b, p-ClC6H4, CH3
2c, p-BrC6H4, CH3
2d, p-IC6H4, CH3
2e, p-CH3C6H4, CH3
2f, p-CH3OC6H4, CH3
2g, Ph, Ph
2h,
1.5
O
2h,
2i,
9
0.5
0.5
3i, 35
3j, 63
O
O
2i,
10
2j,
O
N
2j,
2k, CH3, CH3
11
12
13
0.5
0.5
0.5
3k, 46
3l, 57
2l, CH3, CH3CH2
2m, CH3, (CH3)2CHCH2
3m, 70
Reactions were carried out with 0.75 mmol of 1a, 0.5 mmol of ketones, and 0.5 mmol of tert-BuOK
a
Yield of isolated product after chromatography
123

Efficient solvent-free synthesis of tertiary propargylic alcohols
2395
Table 3 tert-BuOK promoted alkynylation reactions of various ethynylbenzene derivatives with
4-methylacetophenone (2e)
O
OH
tert-BuOK
R
R
+
neat, r.t.
H3C
CH3
4a-d
1b-e
2e
Entry
1, R
Reaction time (h)
4, Yield (%)a
1
2
3
4
1b, Cl
1
4a, 75
4b, 74
4c, 40
4d, 45
1c, Br
1
1d, CH3
1e, CH3O
0.5
0.5
Reactions were carried out with 0.75 mmol of ethynylbenzene derivatives, 0.5 mmol of 2e, and 0.5 mmol
of tert-BuOK
a
Yield of isolated product after chromatography
O
OH
tert-BuOK
+
Ph
Me
neat, r.t., 30 min
83%
2a (8.3 mmol)
1a (12.5 mmol)
1a (8.3 mmol)
1a (15.0 mmol)
3a
Ph
O
HO
tert-BuOK
+
+
neat, r.t., 30 min
80%
2h (5.6 mmol)
3h
OH
O
tert-BuOK
CH CCH CHCH
3
3
2
neat, r.t., 30 min
75%
CH3
2m (10.0 mmol)
Ph
3m
Scheme 2 Large-scale reactions
Conclusions
We have developed a mild and efficient method for the preparation of tertiary
propargylic alcohols based on the alkynylation of arylacetylenes with ketones
promoted by tert-BuOK under solvent-free conditions. This new green process
deserves consideration due to its practicality. The reaction is not only suitable for
aromatic ketones but also applicable to aliphatic substrates.
123

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S. Chen et al.
Experimental
All reagents were used as received from commercial sources, unless specified
otherwise, or prepared as described in the literature. 1H and 13C NMR spectra were
recorded at 500 and 125 MHz with an Avance 500 Brucker spectrometer. Chemical
shifts are reported in ppm using tetramethylsilane as internal standard when CDCl3
was used as solvent. IR spectra were recorded with a NEXUS-670FT infrared
spectrometer. HRMS were obtained on a Brucker Apex IV FTMS.
General procedure
A mixture of terminal alkyne 1a (77.0 mg, 0.75 mmol), tert-BuOK (56.0 mg, 0.5 mmol),
and carbonyl compound 2a (60.0 mg, 0.5 mmol) was placed into a reaction flask (10 mL)
at room temperature. The progress of reaction was monitored by TLC. After completion of
the reaction, the resulting mixture was isolated by flash column chromatography over
silica gel to afford 2,4-diphenylbut-3-yn-2-ol 3a in 81 % yield.
Spectroscopic data for the products
2,4-Diphenylbut-3-yn-2-ol (3a)
1H NMR (500 MHz, CDCl3) d 1.85 (s, 3H), 2.71 (s, 1H), 7.29 (t, J = 12.5 Hz, 4H),
7.36 (t, J = 13.0 Hz, 2H), 7.45 (t, J = 7.0 Hz, 2H), 7.71 (d, J = 7.0 Hz, 2H).
2-(4-Chlorophenyl)-4-phenylbut-3-yn-2-ol (3b)
1H NMR (500 MHz, CDCl3) d 1.82 (s, 3H), 2.84 (s, 1H), 7.30 (d, J = 6.5 Hz, 5H),
7.44 (t, J = 7.5 Hz, 2H), 7.62 (d, J = 8.5 Hz, 2H).
2-(4-Bromophenyl)-4-phenylbut-3-yn-2-ol (3c)
1H NMR (500 MHz, CDCl3) d 1.82 (s, 3H), 2.80 (s, 1H), 7.31 (t, J = 8.5 Hz, 3H),
7.43–7.47 (m, 4H), 7.56 (d, J = 8.5 Hz, 2H).
2-(4-Iodophenyl)-4-phenylbut-3-yn-2-ol (3d)
IR (KBr): 3,527, 3,054, 3,023, 2,992, 2,928, 2,857, 2,231, 1,615, 820, 758, and
717 cm-1 1H NMR (500 MHz, CDCl3) d 1.81 (s, 3H), 2.80 (s, 1H), 7.29
;
(d, J = 6.0 Hz, 3H), 7.43 (d, J = 7.0 Hz, 4H), 7.66 (d, J = 8.0 Hz, 2H); 13C NMR
(125 MHz, CDCl3) d 33.4, 70.1, 85.3, 91.9, 93.5, 122.3, 127.2, 128.4, 128.7, 131.8,
145.5; HRMS calcd for C16H13IO: 348.0011. Found: 348.0013.
2,4-Dip-tolylbut-3-yn-2-ol (3e)
1H NMR (500 MHz, CDCl3) d 1.84 (s, 3H), 2.35 (s, 3H), 2.59 (s, 1H), 7.17
(d, J = 7.5 Hz, 2H), 7.30 (s, 3H), 7.46 (s, 2H), 7.59 (d, J = 7.5 Hz, 2H).
123

Efficient solvent-free synthesis of tertiary propargylic alcohols
2397
2-(4-Methoxyphenyl)-4-phenylbut-3-yn-2-ol (3f)
1H NMR (500 MHz, CDCl3) d 1.85 (s, 3H), 2.60 (s, 1H), 3.80 (s, 3H), 6.89
(d, J = 8.0 Hz, 2H), 7.32 (s, 3H), 7.47 (d, J = 3.5 Hz, 2H), 7.64 (d, J = 8.5 Hz, 2H).
1,1,3-Triphenylprop-2-yn-1-ol (3g)
1H NMR (500 MHz, CDCl3) d 2.93 (s, 1H), 7.25 (t, J = 14.5 Hz, 2H), 7.29–7.33
(m, 7H), 7.48 (t, J = 7.5 Hz, 2H), 7.66 (d, J = 7.5 Hz, 4H).
9-(Phenylethynyl)-9H-fluoren-9-ol (3h)
1H NMR (500 MHz, CDCl3) d 2.78 (s, 1H), 7.22 (d, J = 8.0 Hz, 3H), 7.30–7.39
(m, 6H), 7.58 (d, J = 7.5 Hz, 2H), 7.73 (d, J = 7.5 Hz, 2H), 7.73 (d, J = 7.5 Hz, 2H).
2-(Furan-2-yl)-4-phenylbut-3-yn-2-ol (3i)
1H NMR (500 MHz, CDCl3) d 1.72 (s, 3H), 2.61 (s, 1H), 6.36 (s, 1H), 6.46
(d, J = 3.0 Hz, 1H), 7.32 (d, J = 6.0 Hz, 3H), 7.42 (s, 1H), 7.46 (t, J = 7.5 Hz, 2H).
4-Phenyl-2-(pyridin-2-yl)but-3-yn-2-ol (3j)
1H NMR (500 MHz, CDCl3) d 1.88 (s, 3H), 5.71 (s, 1H), 7.23–7.28 (m, 4H),
7.42–7.44 (m, 2H), 7.68 (d, J = 8.0 Hz, 1H), 7.73–7.76 (m, 1H), 8.52
(d, J = 3.5 Hz, 1H).
2-Methyl-4-phenylbut-3-yn-2-ol (3k)
1H NMR (500 MHz, CDCl3) d 1.60 (s, 6H), 2.58 (s, 1H), 7.28 (t, J = 5.0 Hz, 3H),
7.41 (t, J = 7.0 Hz, 2H).
3-Methyl-1-phenylpent-1-yn-3-ol (3l)
1H NMR (500 MHz, CDCl3) d 1.10 (t, J = 15.0 Hz, 3H), 1.57 (s, 3H), 1.75–1.83
(m, 2H), 2,27 (s, 1H), 7.29 (d, J = 2.0 Hz, 3H), 7.41 (t, J = 6.5 Hz, 2H).
3,4-Dimethyl-1-phenylpent-1-yn-3-ol (3m)
1H NMR (500 MHz, CDCl3) d 1.05 (t, J = 12.0 Hz, 7H), 1.65 (s, 3H), 1.69
(d, J = 6.0 Hz, 2H), 1.97–2.04 (m, 1H), 2.21,(s, 1H), 7.29 (t, J = 6.0 Hz, 3H), 7.40
(t, J = 7.0 Hz, 2H).
4-(4-Chlorophenyl)-2-p-tolylbut-3-yn-2-ol (4a)
IR (KBr): 3,533, 3,030, 2,998, 2,923, 2,864, 2,230, 1,616, 826, and 719 cm-1
;
1H NMR (500 MHz, CDCl3) d 1.85 (s, 3H), 2.36 (s, 3H), 2.43(s, 1H), 7.19
123

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S. Chen et al.
(d, J = 5.0 Hz, 2H), 7.29 (d, J = 5.0 Hz, 2H), 7.39 (d, J = 5.0 Hz, 2H), 7.58
(d, J = 5.0 Hz, 2H); 13C NMR (125 MHz, CDCl3) d 21.1, 33.1, 70.3, 93.6, 121.1,
124.9, 128.7, 129.1, 133.0, 134.5, 137.6, 142.6; HRMS calcd for C17H15ClO:
270.0811. Found: 376.0461.
4-(4-Bromophenyl)-2-p-tolylbut-3-yn-2-ol (4b)
IR (KBr): 3,478, 3,061, 3,027, 2,993, 2,920, 2,861, 2,227, 1,617, 821, and
1
720 cm-1; H NMR (500 MHz, CDCl3) d 1.84(s, 3H), 2.36(s, 3H), 2.47 (s, 1H),
7.19 (d, J = 6.0 Hz, 2H), 7.32 (d, J = 7.0 Hz, 2H), 7.44 (d, J = 6.5 Hz, 2H), 7.58
(d, J = 6.5 Hz, 2H); 13C NMR (125 MHz, CDCl3) d 21.1, 33.1, 70.3, 83.7, 93.8,
121.6, 122.7, 124.9, 129.1, 131.6, 133.2, 137.6, 142.5; HRMS calcd for C17H15BrO:
314.0306. Found: 314.0303.
2,4-Dip-tolylbut-3-yn-2-ol (4c)
1
IR (KBr): 3,548, 3,029, 2,988, 2,921, 2,862, 2,230, 1,615, 817, and 720 cm-1; H
NMR (500 MHz, CDCl3) d 1.85 (s, 3H), 2.35 (d, J = 4.0 Hz, 6H), 2.42 (s, 1H),
7.12 (d, J = 8.0 Hz, 2H), 7.18 (d, J = 7.5 Hz, 2H), 7.36 (d, J = 6.0 Hz, 2H), 7.61
(d, J = 8.0 Hz, 2H); 13C NMR (125 MHz, CDCl3) d 21.2, 21.5, 70.3, 84.9, 91.9,
119.6, 125.0, 129.0, 131.6, 137.4, 138.6, 142.9; HRMS calcd for C18H18O:
250.1358. Found: 250.1357.
4-(4-Methoxyphenyl)-2-p-tolylbut-3-yn-2-ol (4d)
IR (KBr): 3,549, 3,030, 2,987, 2,958, 2,923, 2,801, 2,229, 1,604, 815, and
1
720 cm-1; H NMR (500 MHz, CDCl3) d 1.83 (s, 3H), 2.35 (t, J = 13.5 Hz, 3H),
2.71 (s, 1H), 3.76 (s, 3H), 6.81 (d, J = 8.5 Hz, 2H), 7.15 (d, J = 8.5 Hz, 2H), 7.37
(d, J = 8.5 Hz, 2H), 7.59 (d, J = 8.0 Hz, 2H); 13C NMR (125 MHz, CDCl3) d 21.1,
33.4, 55.3, 70.3, 84.7, 91.4, 114.0, 114.8, 125.0, 129.0, 133.2 137.4, 143.1, 159.7;
HRMS calcd for C18H18O2: 266.1307. Found: 266.1309.
Acknowledgments The project is generously supported by National Natural Science Foundation of
China (Nos. 20902044 and 21102068), Natural Science Foundation of Inner Mongolia of China
(No. 2009BS0204) and ‘‘Chunhui’’ Program from Ministry of Education of China (Z2009-1-01003).
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