A convenient synthesis of aromatic-ring-substituted diacetylenes

Article abstract of DOI:10.1002/(SICI)1522-2675(19990113)82:1<138::AID-HLCA138>3.0.CO;2-G

A simple and convenient way for the preparation of symmetrical diarylbutadiynes 5 with improved yields is reported (Scheme2). The reaction time is drastically reduced using this method compared to previously reported procedures.

Full text of DOI:10.1002/(SICI)1522-2675(19990113)82:1<138::AID-HLCA138>3.0.CO;2-G

138
Helvetica Chimica Acta ± Vol. 82 (1999)
A Convenient Synthesis of Aromatic-Ring-Substituted Diacetylenes
by Abhijit Sarkar*, Shuji Okada, and Hachiro Nakanishi
Institute for Chemical Reaction Science, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan
and Hiro Matsuda
National Insititute for Materials and Chemical Research, 1-1 Higashi, Tsukuba 305-65, Japan
A simple and convenient way for the preparation of symmetrical diarylbutadiynes 5 with improved yields is
reported (Scheme 2). The reaction time is drastically reduced using this method compared to previously
reported procedures.
1. Introduction. ± Diacetylenes have generated a lot of interest among researchers
during the last two decades due to its peculiar solid-state polymerization behaviour
[1][2]. One class of diacetylenes which we have been investigating consists of aryl and
heteroaryl moieties directly bound to the diacetylene backbone. The preparation of
such diacetylenes 5 using reported procedures involves several steps starting with aryl
halide or heteroaryl halide 1 and is generally achieved via 3 and 4 following Scheme 1
[3 ± 6].
Scheme 1
The coupling reaction of aryl halide 1 with 2-methylbut-3-yn-2-ol (2) using the
palladium catalyst [3] [PdCl2(PPh3)2] gives arylalkynol 3. Depending on the reactivity
of the aryl halide, the amount of by-product, 2,7-dimethylocta-3,5-diyne-2,7-diol (6),
varies. Thus, for thienyl halides, which are comparatively less reactive, a considerable
amount of diol is formed, and consequently the yield of 3 decreases [4]. Moreover, this
first step takes 5 ± 12 h to go to completion. The next step, the cleavage of acetone, is
also time-consuming. In the case of thienyl derivatives, the products 4 have to be
distilled at low pressure in spite of rather low boiling points to avoid thermal
polymerization. Lots of care, especially for the cooling of the condenser and receiver,
has to be taken to get the distilled product, even though some of the product is lost
during distillation. The final step, i.e., a coupling reaction using Hayꢀs catalyst [5], is the

Helvetica Chimica Acta ± Vol. 82 (1999)
139
fastest step, but the yield of the produced diacetylene is not much higher than 40% for
aryl- and heteroaryl-substituted compounds. Thus, the overall yield following Scheme 1
generally does not exceed 28% starting from 1, while the reaction process is quite long.
We have now developed a simpler synthetic procedure to obtain symmetrically
substituted aryl- and heteroaryl-diacetylenes (Scheme 2), a procedure which is
significantly faster and involves less cumbersome workup processes, and thus is more
attractive. The yields of the final products 5 are higher than those obtained via the
reactions of Scheme 1. There are previous reports on the synthesis of alkynes using
similar reagents as ours. One of them deals with the synthesis of diarylalkynes starting
from aryl halides [7], while the other one describes the preparation of unsymmetrical
diarylbutadiynes starting from arylhexadiynols [8]. However, they are not intended for
the preparation of symmetrical diacetylenes by a simple procedure.
Scheme 2
2. Results and Discussion. ± According to Scheme 2, we coupled a variety of aryl
halides 1 quite efficiently with 2,7-dimethylocta-3,5-diyne-2,7-diol (6) (Table), the
latter being obtained almost quantitatively from 2 within 3 h (see Exper. Part). Thus,
reaction of 6 with 2 mol-equiv. of 1 in refluxing dioxane in the presence of
benzyltrimethylammonium chloride as phase-transfer catalyst, aqueous NaOH solu-
tion as base, and a mixture of dichlorobis(triphenylphosphine)palladium(II), and
copper(I) iodide as catalyst furnished diacetylenes 5.
Table. Reaction Times and Yields for the Transformation 6 ! 5, and Melting Points of the Diacetylenes 5
Entry
Ar±X (1)
Reaction time [min]
Yield [%] of 5
M.p. [8] of 5
measured
reported
a
b
c
90
90
45
44
47
89
111
228
88 ± 89 [9]
111.5 ± 112.5 [10]
227 [11]
120
d
e
60
60
46
47
171a)
87
±b)
87 ± 88 [13]
a) Started to sublime at this point. b) M.p. was not reported.

140
Helvetica Chimica Acta ± Vol. 82 (1999)
The proposed pathway for the reaction process first involves loss of acetone from
the diol 6 to give alcohol 7 which can react with the aryl halide yielding aryl alcohol 9
(Scheme 3). After a similar cleavage of acetone, 9 is then converted via 10 to butadiyne
5. The intermediates 9 and 10 could be detected in the reaction mixture, suggesting that
the reaction proceeds via the proposed pathway producing 7 at first. The alternative
process from 6 to 10 or 5 via 8, with 8 reacting with the aryl halide, cannot be excluded.
However, butadiyne 8 may leave the mixture before reaction because of its low boiling
point (estimated 10 ± 208/760 Torr) [9].
Scheme 3
By-product formation was negligible, and in some cases, the starting material 1 did
not react completely, but the unreacted portion could be recovered in such cases.
Therefore, the production of 8 is considered to be the main reason for a reduction of
the yield of 5. Nevertheless, the yield of 5 [10 ± 14] starting from 2 via 6 was in the range
of 38 ± 42% which is significantly higher than that from the previously reported process
(Scheme 1). Inert atmosphere was absolutely necessary for the reaction 6 ! 5 to
proceed, and all the reagents had to be purged with N2 before use.
In conclusion, we have developed a convenient, efficient, and general method for
the preparation of symmetrical diarylbutadiynes starting from the corresponding aryl
halides and 2,7-dimethylocta-3,5-diyne-2,7-diol.
Experimental Part
2,7-Dimethylocta-3,5-diyne-2,7-diol (6). Through a mixture of CuCl (4 g), NH4Cl (15 g), H2O (45 ml), and
2-methylbut-3-yn-2-ol (2; 0.35 mol), oxygen was bubbled under vigorous stirring. The soln. gradually became
warm. After 45 min, more 2 (0.35 mol) was added, and finally, the last portion of 2 (0.35 mol) was added after 90
min. The end of the reaction was indicated by a distinct change of color. The mixture was cooled to ca. 208, and
36% aq. HCl soln. (10 ml) was added while stirring. The mixture was extracted several times with THF, the THF
layer dried (Na2SO4) and evaporated, and the crude recrystallized from hexane/AcOEt at ca. 108: three crops of
needle-shaped colorless crystals. Yield of 6 about quant. M.p. 1298 ([9]: 1298 ± 1308).
Diacetylenes 5: General Procedure. A mixture of dichlorobis(triphenylphosphine)palladium(II) (0.07 g,
0.1 mmol), CuI (0.02 g, 0.1 mmol), and benzyltriethylammonium chloride (0.02 g, 0.1 mmol) was flushed with
N2. Separately, 6 (0.166 g, 1 mmol) and aryl halide (2 mmol) in dioxane (5 ml) were purged with N2 for 15 min.
This soln. was then rapidly added to the mixture [PdCl2(PPh)3]/CuI/(PhCH2NEt3)Cl, followed by 5.5n NaOH
(2.5 ml) which was added by syringe. The resulting soln. was refluxed under N2 (TLC monitoring). Upon
completion, a sat. NH4Cl soln. (5 ml) was added, the mixture stirred for ca. 30 min at r. t. and then extracted with
Et2O (3 Â). The extract was dried (Na2SO4) and evaporated, and the crude product submitted to column
chromatography (silica gel, hexane/AcOEt): pure 5. Yields and data of 2,2'-(buta-1,3-diyne-1,4-diyl)bis[thio-

Helvetica Chimica Acta ± Vol. 82 (1999)
141
phene] (5a), 3,3'-(buta-1,3-diyne-1,4-diyl)bis[thiophene] (5b), 3,3'-(buta-1,3-diyne-1,4-diyl)bis[quinoline] (5c),
5,5'-(buta-1,3-diyne-1,4-diyl)bis[pyrimidine] (5d), and 1,1'-(buta-1,3-diyne-1,4-diyl)bis[benzene] (5e): Table.
A.S. is grateful to the Japanese Society for the Promotion of Science (JSPS) for the award of a postdoctoral
research fellowship.
REFERENCES
[1] ꢁPolydiacetylenesꢀ, Eds. D. Bloor and R. R. Chance, NATO ASI Series, Series E, Applied Sciences No. 102,
Martinus Nijhoff, Dordrecht, 1984.
[2] S. Okada, H. Nakanishi, in ꢁPolymeric Materials Encyclopediaꢀ, Ed. J. C. Salamone, CRC Press, Boca
Raton, 1996, pp. 8393.
[3] K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron Lett. 1975, 16, 4467.
[4] A. Sarkar, P. Sekher, M. B. Kamath, L. P. Bhagwat, K. N. Babu, K. Rajalakshmi, S. S. Talwar, Indian. J.
Chem., Sect. B 1991, 30, 360.
[5] A. S. Hay, J. Org. Chem. 1962, 27, 3320.
[6] A. Vaitiekunas, F. F. Nord, J. Am. Chem. Soc. 1954, 76, 2733; U. Fritzsche, S. Hünig, Tetrahedron Lett. 1972,
13, 4831.
[7] A. Caprita, A. Lessi, R. Rossi, Synthesis 1984, 571.
[8] S. A. Nye, K. T. Potts, Synthesis 1988, 375.
[9] L. Brandsma, ꢁPreparative Acetylenic Chemistryꢀ, Elsevier, Amsterdam, 1st edn., 1971.
[10] A. F. Garito, C. C. Teng, K. Y. Wong, O. K. Zhamani, Mol. Cryst. Liq. Cryst. 1984, 106, 219.
[11] J. L. Buttler, M. Gordon, J. Heterocycl. Chem. 1975, 12, 1015.
[12] A. Sarkar, K. N. Babu, M. B. Kamath, P. K. Khandelwal, L. P. Bhagwat, S. S. Talwar, in ꢁFrontiers of
Polymer Researchꢀ, Eds. P. N. Prasad, J. K. Nigam, Plenum, New York, 1991, p 233.
[13] W. H. Kim, N. B. Kodali, J. Kumar, S. K. Tripathy, Macromolecules 1994, 27, 1819.
[14] J. B. Armitage, N. Entwistle, E. R. H. Jones, M. C. Whiting, J. Chem. Soc. 1954, 147.
Received October 12, 1998