CC BY
26
УДК 547.741+547.322+547.385.1
Вестник СПбГУ. Сер. 4. Т. 1 (59). 2014. Вып. 4
L. N. Sobenina, B. A. Trofimov
PALLADIUM-FREE ETHYNYLATION OF PYRROLES AND INDOLES WITH HALOALKYNES IN METAL OXIDES AND SALTS MEDIUM
A. E. Favorsky Institute of Chemistry, Siberian Branch of the RAS, 644033 Irkutsk, Russian Federation
New palladium-free cross-coupling between substituted pyrroles, 4,5,6,7-tetrahydroindoles or indoles and haloacetylenes in metal oxides and salts medium (MgO, CaO, ZnO, BaO, Al2O3, K2CO3) regioselectively affording 2-ethynylpyrroles, 2-ethynyl-4,5,6,7-tetrahydroindoles or 3-ethynylindoles is discussed. The reactions proceed at room temperature under solvent-free conditions without catalysts. The yields of ethynylation products most often range from 60 to 70 %, in certain cases reaching 90—94 %. Refs 35. Tables 1.
Keywords: cross-coupling, haloacylacetylenes, halopropynoates, indoles, pyrroles, metal oxides and salts, 2-acylethynylpyrroles, ethyl 3-(4,5,6,7-tetrahydroindol-2-yl)-2-propynoates.
Л. Н. Собенина, Б. А. Трофимов
БЕСПАЛЛАДИЕВОЕ ЭТИНИЛИРОВАНИЕ ПИРРОЛОВ И ИНДОЛОВ ГАЛОГЕНАЛКИНАМИ В ПРИСУТСТВИИ СОЛЕЙ И ОКСИДОВ МЕТАЛЛОВ
Иркутский институт химии им. А. Е. Фаворского СО РАН, 644033 Иркутск, Российская Федерация
Обсуждается новое беспалладиевое кросс-сочетание замещённых пирролов, 4,5,6,7-тет-рагидроиндолов или индолов с галогеноацетиленами в присутствии оксидов металлов и их солей (MgO, CaO, ZnO, BaO, AI2O3, K2CO3), региоселективно приводящее к 2-этинилпирро-лам, 2-этинил-4,5,6,7-тетрагидроиндолам или 3-этнилиндолам. Реакции протекают при комнатной температуре и без растворителя. Выходы продуктов этинилирования составляют 60—70 %, а в некоторых случаях достигают 90—94 %. Библиогр. 35 назв. Табл. 1.
Ключевые слова: кросс-сочетание, галогенацетилены, галогенопропионаты, индолы, пир-роллы, оксиды металлов и соли, 2-ацилэтинилпирролы, этил 3-(4,5,6,7-тетрагидроиндол-2-ил)-2-пропионты.
The steady interest in pyrrole chemistry is owing, first of all, to the fact that the pyrrole moiety constitutes a core of numerous biologically important compounds such as chlorophyll, hemoglobin, vitamin B12, alkaloids, etc. participating in biotransformation of solar energy, oxygen transfer processes and other life-sustaining reactions [1, 2].
Currently, pyrroles, including functionally substituted ones, are intensively employed in the synthesis of natural compound congeners [3], as pharmacophores [4-7] and building blocks for drug design. For example, anticancer antibiotic CC-1065 [8, 9] incorporates the pyrrole fragment in its structure. The Lipitor (Atorvastatin), one of the best selling drugs in pharmaceutical history used for lowering blood cholesterol, represents functionalized 2,3-di-phenylpyrrole [10, 11].
Functionalized pyrroles draw attention as molecular optical switches (including superfast ones) for design of photo- and electroconducting devices, micro- and nanomachines [12-14], and also as ligands for new photocatalysts and synthetic biologically active complexes [15].
In this line, functionalization of pyrroles represents an urgent challenge. Among universal types of reactive carriers of the pyrrole moiety, suitable for various purposes of organic synthesis, are their ethynyl derivatives. In the pyrrole nucleus, the presence of acetylene function, which is sensitive towards nucleophilic, radical and electrophilic attacks as well
as to cycloaddition and polymerization, defines importance of these compounds as highly reactive multi-faceted building blocks.
Therefore a great deal of research efforts is invested in the development of efficient methods for the synthesis of ethynylpyrroles, especially those bearing strong acceptor substituents at the triple bond.
The interest in such acetylenes is obvious: the strong electron-acceptor at the triple bond dramatically increases its electrophilicity that allows performing the reaction of nu-cleophilic addition (typical for acetylenes) under very mild conditions, often quantitatively and stereoselectively, without catalysts and superbase reagents.
However introduction of such activated acetylenic substituents into the pyrrole scaffold remained until recently a stubborn problem since the known methods (for example, Sonogashira reaction [16-19]) were limited by the synthesis of acetylenes containing donor functionalities only. Besides, almost all common methods for ethynylation of the pyrrole ring require its preliminary functionalization, mainly with halogens.
In 2004 we have developed [20-22] a fundamentally new method for direct regioselective introduction of acetylenic substituents in the position 2 of the pyrrole ring or position 3 of the indole moiety. The method comprises the reaction of pyrroles or indoles with electron-deficient haloacetylenes on the surface of aluminum oxide.
Thus pyrroles readily react with acylbromoacetylenes on the surface of aluminium oxide to afford 2-(acylethynyl)pyrroles 1 (Scheme (1)) [20-22].
The reaction occurs at room temperature and is slightly exothermic. It is entirely regioselective: even impurities of isomeric 1- or 3-(acylethynyl)pyrroles are not detected in the reaction mixture. Ethynylation proceeds via the addition of pyrroles to the triple bond of haloacetylene to deliver bromoethenylpyrroles 2, which are isolated in small amounts. Pyrroles 2 are ^-isomers with cis-orientation towards the position of the carbonyl group and olefinic bond. Such conformation leads to intramolecular hydrogen bonding of NH proton with oxygen atom of the carbonyl function that stabilizes this isomer. This is why this isomer can be isolated. Side products, dipyrrolylethenes 3, are likely formed via the substitution of bromine atom in bromoethenylpyrroles 2 , since pyrroles themselves do not add to ethynylpyrroles under the reaction conditions. The yields of dipyrrolylethenes 3 usually do not exceed 20 %, but when pyrroles are used in two-fold molar excess, the yields can reach 40 %.
The question arises of whether ethynylpyrroles are really formed due to elimination of HBr molecule from the primary adducts of the reaction, bromoethenylpyrroles. To answer this question, we have performed NMR monitoring of the reactions between 2-arylpyrro-les 4a-d and benzoylbromoacetylene (Scheme (2)) [23]. It is found that the reactions give
ethynyl- (5a-d) and bromoethenylpyrroles 6a-d in a ratio, which changes insignificantly with time (Table 1).
R-^- H 4a-d
T\ Ph
+ Br = / -
20-25 "C, 30-60 min
Al2O3
R
0-19 % 6a-d
f\ .Br
\ +
R
R = H (a), Me2N (b), MeO (c), Cl (d)
T w Cf H
5a-d 45-94 % R
NH
h 7a-d 0-5 %
Ph
(2)
H NMR monitoring of the reaction between 2-arylpyrroles 4a-d with benzoylbromoacetylene
R
Reaction time, min
10
30
60
Composition of the reaction mixture, % (yield, %)
5 6 5 6 5 6
H 75 25 74 26 78 22
Me2N 51 traces 64 traces 70 traces
MeO 53 17 59 19 64 22
Cl 72 18 79 21 81 (94) 19 (3)
+
Apparently, the constant ratio of these products can be rationalized as follows. The pyrroles add to acetylene according to the rule of trans-nucleophilic addition to deliver Z-isomers of bromoethenylpyrroles 6a-d. The latter partially eliminate HBr giving ethynylpyrroles 5a-d, and partially isomerize into the ^-isomers stabilized by strong intramolecular bonding (Scheme (3)). Since cis-elimination proceeds slower than trans-elimination, a certain amount of ^-bromoethenylpyrroles 6a-d remains in the reaction mixture.
The fact that ethynylpyrroles 5a-d are formed from bromoethenylpyrroles 6a-d can be confirmed by comparison of their concentration in the reaction mixture with isolated yields. During the purification by column chromatography on aluminum oxide, the reaction continues giving ethynylpyrroles 5a-d in higher yields and bromoethenylpyrroles 6a-d in lower yields. Besides, one should bear in mind that preliminarily isolated 2-(1-bromo-2-benzoylethenyl)-5-(4-chlorophenyl)pyrrole (6d) is easily transformed to the corresponding
ethynylpyrrole 5d (Scheme (4)). All this confirms that bromides 6a-d are intermediate products of the cross-coupling.
Cl
Br
- HBr
Cl
Ph
H
5d
(4)
92 %
Unlike NH-pyrroles, the interaction of 1-vinyl- (7a-c) and 1-isopropenylpyrroles 8a-c with benzoylbromoacetylene on aluminum oxide exclusively affords the cross-coupling products 9a-c, 10a-c (Scheme (5)) [24]. In this case, neither dipyrrolylethenes nor the reaction intermediates (bromoethenylpyrroles) are detected. Probably, the latter are not found in the reaction mixture due to the lack of possibility of their stabilization by intramolecular hydrogen bonding.
AW
J\
Ph
N + Br = {
>iA
O
20-25 "C, 1 h
R1 """ 7a-c, 8a-c R1 = H (7, 9), Me (8, 10); R2 = R3 = H (a) R2 = Ph, R3 = H (b); R2-R3 = (CH2)4 (c)
R3
R2
Ph
R
1
O
(5)
9a-c, 10a-c
42-70 %
Alo
1ff-2-(Benzoylethynyl)pyrroles 6a, 11a, b are isolated as side-products of 1-isopropen-ylpyrroles 8a-c ethynylation. They are likely formed owing to hydrolysis of the isopropenyl group of ethynylpyrroles catalyzed by eliminating HBr since hydrate water is always present in Al2O3 (Scheme (6)).
R3
r n
R3
O
Ph Al2O3 / H2O / HBr R2"^n
-^ zk
OH
Ph
O
R
R2 = R3 = H (11a)
- Me CO
il
N' i
H
Ph
R2 = Ph, R3 = H (6a); R2-R3 = (CH2)4 (11b) 6a, 11a, b
O
(6)
R2
There is another example of the pyrrole ring ethynylation with benzoylbromoacety-lene in the presence of aluminum oxide. The corresponding 2-benzoylethynyl-5-(1,1-diphe-nyl)pyrroles 12a-d are synthesized in 35-46 % yields from 2-(1,1'-diphenyl-4-yl)pyrroles 13a, b and their 1-vinyl derivatives 13c, d (Scheme (7)) [25]. In this case, the reaction proceeds slower than with 2-phenylpyrrole. A side product of the reaction is dibro-mophenylpropenone 14, an adduct of bromobenzoylacetylene with HBr, which is released upon ethynylation.
R2
Ph
13a-d
R1 = H; R2 = H (a), Ph (b) R1 = CH=CH2; R2 = H (c), Ph (d)
R2
Ph +
12a-d
Br r
^ _J
14
The reaction of 2-(2-furyl)- and 2-(2-thienyl)pyrroles with acylbromoacetylenes is of special interest. The presence of two five-membered aromatic rings capable of ethynylation equivocate outcome of these. It appears that in the case of 1H- and 1-vinyl-2-(2-thien-yl)pyrroles, the reaction proceeds selectively to deliver 2-(2-thienyl)pyrroles 15a-f bearing acetylenic substituents in the pyrrole ring (Scheme (8)).
R3 O
15a-f
R1 = H; R2 = Ph (a), 2-furyl (b), 2-thienyl (c) R1 = CH=CH2; R2 = Ph (d), 2-furyl (e), 2-thienyl f)
(8)
Al2O3
Under these conditions, 2-(2-furyl)pyrrole and its N-vinyl derivative react in other fashion: along with the main direction of the reaction (ethynylation of the pyrrole ring), the attack of a-position of the furan moiety at the triple bond takes place (Scheme (9)). The ratio of ethynylation products across the pyrrole (16a-f ) and furan (17a-f ) cycles is « 5:1 (XH NMR).
V \\ N
R1
R3
O
R2
R2
O
17a-f
(9)
R1 = H; R2 = Ph (a), 2-furyl (b), 2-thienyl (c) R1 = CH=CH2; R2 = Ph (d), 2-furyl (e), 2-thienyl f)
Al2O3
The results obtained can be considered as a discovery of new reaction of direct palladiumfree ethynylation of the furan ring with functional haloacetylenes.
Indole and 2-methylindole smoothly react with benzoylbromoacetylene on the surface of aluminum oxide to furnish 3-benzoylethynylindoles 18a, b (R = Ph, Scheme (10)) [26]. It is the first example of the indole nucleus direct ethynylation. Without aluminum oxide, as in the case of pyrroles, the ethynylation does not take place. The only side-products, diin-dolylethenes, are formed in negligible amounts. With bromopropynoate, the corresponding ethynylation products 18c, d (R2 = OEt, Scheme (10)) are produced in 17 % and 12 % yields [27].
\J \
H
R1
R2 = Ph: R1 = H (a), Me (b) R2 = OEt: R1 = H (c), Me (d)
O
R2
H
18a-d
19a-d
(10)
The reaction of a fused indole, benz[g]indole, with benzoylbromoacetylene under the same conditions gives a mixture of 3- (20) and 2-ethynylindoles 21 in 45 % total yield (Scheme (11)) [26]. In this case, the reaction mixture contains also ^-isomer of 2-bromo-ethenylbenz[g]indole 22 stabilized by intramolecular hydrogen bonding.
n vo
U r^NT
Br—
Ph
A1JO3, 20-25 "C, 60 min
in
N
I
H
21: 22 %
O
O
Ph
H
20: 23 %
Ph +
22
Br
j Ph
(11)
4,5-Dihydrobenz[g]indole, which is a pyrrole by nature, readily reacts with benzoylbro-moacetylene in the presence of aluminum oxide to afford 2-ethynylpyrrole 23 (Scheme (12)) [26]. Dipyrrolylethene 24 is isolated from the reaction mixture in 9 % yield [26].
+
Al2O3, 20-25 "C, 60 min
O
+
+
Thus, we have shown that pyrrole and indoles are easily ethynylated with haloacetylenes on the surface of aluminum oxide.
This brings up another question, whether aluminum oxide is a unique active surface for implementation of the cross-combination or other oxides and salts can also promote this reaction. To answer this question, we have investigated the interaction of 2-phenylpyrrole with benzoylbromoacetylene in the presence of metal oxides (ZnO, BaO, Al2O3, MgO, CaO, TiO2, ZrO2) without solvent [28]. It turns out that this reaction, depending on the active
surface, leads to either cross-coupling product 25 or 2-phenylpyrrole adduct to acetylene triple bond (compound 26) (Scheme (13)). Activity of metal oxides in the ethynylation reaction drops as follows: ZnO (81 %), BaO (73 %), Al2O3 (71 %), MgO (69 %), CaO (50 %) (in brackets, the content of benzoylethynylpyrrole 25 in the reaction mixture is given).
O Ph
(13)
26
"Ph
27
Ph
AS = MgO, CaO, BaO, Al2O3, SiO2, TiO2, ZrO2, CaCO3, ZrSiO4
Like on aluminum oxide, the cross-coupling on these surfaces is accompanied by formation of insignificant amounts of bromoethenylpyrrole 26 and dipyrrolylethene 27.
Titanium, zirconium and silicon [29] dioxides, inactive in the cross-coupling, are specific catalysts of regio- and stereoselective addition of pyrroles to the triple bond of benzoylbro-moacetylene giving rise to bromoethenylpyrrole 26. The latter is prepared and purified on zirconium oxide in 60 % yield [28]. When purification is performed on aluminum oxide, only ethynylpyrrole 25 is formed, and it crystallizes exclusively as a rotamer with a cis-configuration of the NH and CO groups [28]. Meanwhile, 2-benzoylethynyl-5-phenylpyrrole, obtained from 2-phenylpyrrole and benzoylbromoacetylene on the surface of aluminum oxide, gives two crystalline modifications with the carbonyl group oriented toward cis- and trans-position relative to the nitrogen atom [30]. In this case, isolation of ethynylpyrrole 25 mainly as cis-rotamer is likely explained by Al2O3-induced cis-elimination of HBr from Eisomer of bromoethenylpyrrole 26 with instant stabilization of cis-oriented N—H and C=O bonds to the macrocyclic dimer (Scheme (14))
(14)
Thus, the cross-coupling of pyrroles with acylbromoacetylenes in the presence of aluminum oxide leads mainly to acylethynylpyrroles. The reactions of pyrroles with chloro-and iodobenzoylacetylenes proceed under these conditions in a similar fashion. Only the reaction rate changes, while its direction remains intact: in this case, nature of the halogen at the triple bond does not influence the process course.
Under close conditions, bromopropynoate reacts with a tetrahydroindole to furnish bro-mopropenoate 28 as a major product (Scheme (15)) [31]. When aluminum oxide is used in 50-fold excess, the only reaction products are tetrahydroindolylpropynoate 29 and ditetrahy-droindolylacrylate 30, the latter being prevailing. The yield of tetrahydroindolylpropynoate 29 increases up to 58 %, when 10 % potassium carbonate is added to aluminum oxide.
+
+
+
OEt 30: 14 %
Unlike bromopropynoate, iodopropynoate reacts with tetrahydroindole on the surface of aluminum oxide (used both in 10-fold and 50-fold excess) of various basicity to exclusively form ditetrahydroindolylacrylate 30 (Scheme (16)) [31].
H
O
+ i
Al2O3
OEt
20-25 "C, 1 h
(16)
30: 79 %
OEt
Tetrahydroindole reacts with bromopropynoate without aluminum oxide and solvent to give unstable ditetrahydroindolylbromoethane 31 (Scheme (17)). The latter is treated in chloroform with aqueous K2CO3 followed by elimination of HBr and formation of product 30.
Oí +
O
i
OEt 20-25 "C, 1 h
30
(17)
O: . 31 OEt
It has been shown [31] that the addition of potassium carbonate to aluminum oxide results in the increase of ethynylpyrrole yields. What will happen if pure potassium carbonate is employed as solid surface? It turns out that in this case both tetrahydroindole and its N-substituted derivatives are ethynylated selectively to deliver the corresponding ethynyl derivatives 29 in up to 90 % yields (Scheme (18)) [32].
CjT\ + Br— N
R
O
<
OEt 20-25 "C, 1 h
O
JT\
N
1
R OEt 29a-h: 62-90 %
(18)
R = H (a), Me (b), Bn (c), CH=CH2 (d), /-Pr(CH)CH3 (e), »-Bu(CH)CH3 (f), (CH2)2SEt (g), (CH2)2SPr-w (h)
In the case of bromopropynoate, no side products are detected. Iodopropynoate also selectively react with tetrahydroindole on aluminum oxide to exclusively afford tetrahy-droindolylpropynoate 29a. The content of acrylate 30a in this case is only 2-4 %. In
K2CO3
solvents (diethyl ether, chloroform) this reaction does not proceed either with or without K2CO3. Regioselectivity of the ethynylation is not violated even by such bulky substituents as CH(Me)OPr-i and CH(Me)OBu-n, though the reaction time considerably increases (12 h instead of 1 h) and portion-wise addition of bromopropynoate to the reaction mixture is required. Obviously, the low reaction rate is due to steric shielding of the pyrrole ring position 2 by a substituent.
Thus, we have discovered and now successfully develop the new cross-coupling of pyrroles and indoles with haloacetylenes. The reaction is carried out under mild conditions on solid surfaces of metal oxides and salts, without palladium, copper and solvents. Besides, preliminary functionalization of the pyrrole ring is not required. This cross-coupling essentially complements the available methods of ethynylpyrrole synthesis (including Sonogashira reaction), which do not allow to introduce acetylenic fragments having strong electron-withdrawing substituents into the pyrrole or indole ring, and employ unstable halogenated pyrroles or indoles as starting reagents. The potential of this new cross-coupling is still far from to be exhausted: one can assume that it will tolerate not only halogenated acylacetylenes and propynoates, but also acetylenes with other electron-withdrawing substituents such as sulfonylacetylenes, acetylenecarboxylic acid amides, trifluoromethyl and trifluoroacetyl derivative, etc.
From the moment of its discovery, this reaction arrested the attention and now is cited not only in research papers [33], but also in reviews [34] and monographs [35]. Most often this reaction is referred to as inverse Sonogashira coupling. Though this term was originally proposed by us [20], we do not consider it as good choice, since the chemical essence of such ethynylation has nothing to do with palladium-catalyzed Sonogashira cross-coupling.
References
1. Jones R. A., Bean G. P. The chemistry of pyrroles. London; New York; San Francisco: Academic Press, 1977. 525 p.
2. TrofimovB.A., Mikhaleva A. I., Schmidt E. Yu., Sobenina L. N. Khimiya pirrola. Noviye stranitsy. Novosibirsk: Nauka, 2012. 383 p.
3. Anderson H. J., Loader C. E. The synthesis of 3-substituted pyrroles from pyrrole // Synthesis. 1985. N 4. P. 353-364.
4. Lainton J. A. H., Huffman J. W., Martin B. R., Compton D. R. 1-Alkyl-3-(1-naphthoyl)pyrroles: A new class of cannabinoid // Tetrahedron Lett. 1995. Vol. 36, N 9. P. 1401-1404.
5. DeLeon C. Y., GanemB. A new approach to porphobilinogen and its analogs // Tetrahedron. 1997. Vol. 53, N 23. P. 7731-7752.
6. Jacobi P. A., Coutts L. D., Guo J. et al. New strategies for the synthesis of biologically important tetrapyrroles. The "B, C + D + A" approach to linear tetrapyrroles //J. Org. Chem. 2000. Vol. 65, N 1. P. 205-213.
7. PortevinB., TordjmanC, Pastoureau P. et al. 1,3-Diaryl-4,5,6,7-tetrahydro-2fl-isoindole derivatives: A new series of potent and selective COX-2 inhibitors in which a sulfonyl group is not a structural requisite // J. Med. Chem. 2000. Vol. 43, N 24. P. 4582-4593.
8. Magnus P., Or Y.-S. Initial studies on the synthesis of the antitumor agent CC-1065: 3,4-Disubstitu-ted pyrroles and 3, 3'-bipyrroles //J. Chem. Soc. Chem. Commun. 1983, N 1. P. 26-27.
9. Skladanowski A., Koba M., Konopa L. Does the antitumor ciclopropylpyrroloindole antibiotic CC-1065 cross-link DNA in tumor cells? // Biochem. Pharmacol. 2001. Vol. 61. P. 67-72.
10. Oldfield E. Targeting isoprenoid biosynthesis for drug discovery: Bench to bedside // Acc. Chem. Res. 2010. Vol. 43. P. 1216-1226.
11. Lindsley C. W. The top prescription drugs of 2009 in the US: CNS therapeutics rank among highest grossing // ACS Chem. Neurosci. 2010. Vol. 1. P. 407-408.
12. Hayes R.T., Wasilewski M. R., GosztolaD. Ultrafast photoswitched charge transmission through the bridge molecule in a donorbridgeacceptor system // J. Am. Chem. Soc. 2000. Vol. 122, N 23. P. 5563-5567.
13. HarmjanzM., GillH.S., Scott M. J. Porphodimetheneporphyrin interconversion: A tetrapyrrolic redox-switchable macrocycle // J. Am. Chem. Soc. 2000. Vol. 122, N 42. P. 10476-10477.
14. RurackK., Kollmannsberger M., Daub J. Molecular switching in the near infrared (NIR) with a functionalized boron-dipyrromethene dye // Angew. Chem. Int. Ed. 2001. Vol. 40, N 2. P. 385-387.
15. Sour A., Boillot M.-L., Riviere E., LesotP. First evidence of a photoinduced spin change in an Fe(III) complex using visible light at room temperature // Eur. J. Inorg. Chem. 1999. N 12. P. 2117-2119.
16. Sonogashira K., Tohda Y., Hagihara N. A convinient synthesis of acetylenes: catalytic substitutions of acetylenic hydrogen with bromoalkenes, iodoarenes, and bromopyridines // Tetrahedron Lett. 1975. Vol. 16, N 50. P. 4467-4470.
17. Sonogashira K. Comprehensive organic synthesis / eds B.M.Trost, I.Fleming. Oxford: Pergamon Press, 1991.
18. Alvarez A., Guzman A., Ruiz A., Velarde E. Synthesis of 3-arylpyrroles and 3-pyrrolylacetylenes by palladium-catalyzed coupling reactions //J. Org. Chem. 1992. Vol. 57. P. 1653-1655.
19. JacobiP. A. New syntheses of the C,D-ring pyrromethenones of phytochrome and phytocyanin //J. Org. Chem. 2000. Vol. 65. P. 8478-8489.
20. Trofimov B. A, Stepanova Z. V., SobeninaL.N. et al. Ethynylation of pyrroles with 1-acyl-2-bromoacetylenes on alumina: a formal "inverse Sonogashira coupling" // Tetrahedron Lett. 2004. Vol. 45, N 34. P. 6513-6516.
21. Trofimov B. A., Sobenina L. N. Targets in heterocyclic chemistry / eds O. A. Attanasi, D. Spinelli. Roma: Societa Chimica Italiana, 2009. Vol. 13. P. 91-119.
22. Trofimov B. A., Mikhaleva A. I., Schmidt E. Y., SobeninaL.N. Pyrroles and N-vinylpyrroles from ketones and acetylenes: Recent strides // Adv. Heterocycl. Chem. 2010. Vol. 99. Ch. 7. P. 209-254.
23. Trofimov B. A., SobeninaL.N., Stepanova Z. V. et al. Synthesis of 2-benzoylethynylpyrroles by cross-coupling of 2-arylpyrroles with 1-benzoyl-2-bromoacetylene over aluminium oxide // Russ. J. Org. Chem. 2006. Vol. 42, N 9. P. 1348-1355.
24. Trofimov B. A., SobeninaL.N., Stepanova Z. V. et al. Regioselective cross-coupling of 1-vinylpyrroles with acylbromoacetylenes on Al2O3: a synthesis of 1-vinyl-2-(2-acylethynyl)pyrroles // Synthesis. 2007. N 3. P. 447-451.
25. SobeninaL.N., Stepanova Z. V., Petrova O. V. et al. Synthesis of 3-[5-(biphenyl-4-yl)pyrrol-2-yl]-1-phenylprop-2-yn-1-ones by palladium-free cross-coupling between pyrroles and haloalkynes on aluminum oxide // Russ. Chem. Bull. Intern. Ed. 2013. Vol. 62, N 1. P. 88-92.
26. Sobenina L. N., Demenev A. P., Mikhaleva A. I. et al. Ethynylation of indoles with 1-benzoyl-2-bro-moacetylene on Al2O3 // Tetrahedron Lett. 2006. Vol. 47, N 2. P. 7139-7141.
27. Petrova O. V., Sobenina L. N., Ushakov I. A., Mikhaleva A. I. Reaction of indoles with ethyl bromo-propynoate over Al2O3 surface // Russ. J. Org. Chem. 2008. Vol. 44, N 10. P. 1512-1516.
28. Trofimov B. A., SobeninaL. N., Stepanova Z. V. et al. Reactions of 2-phenylpyrrole with bromoben-zoylacetylene on metal oxides active surfaces // Tetrahedron. 2008. Vol. 64, P. 5541-5544.
29. Stepanova Z. V., Sobenina L. N., Mikhaleva A. I. et al. Silica-assisted reactions of pyrroles with 1-acyl-2-bromacetylenes // Synthesis. 2004. N 16. P. 2736-2742.
30. Trofimov B. A. Stepanova Z. V., SobeninaL.N. et al. 2-(2-Benzoylethynyl)-5-phenylpyrrole: fixation of cis- and trans-rotamers in crystal state // Mendeleev Commun. 2005. Vol. 15, N 6. P. 229-232.
31. Trofimov B. A., SobeninaL.N., Demenev A. P. et al. A palladium-and copper-free cross-coupling of ethyl-3-halo-2-propynoates with 4,5,6,7-tetrahydroindoles on alumina // Tetrahedron Lett. 2007. Vol. 48, N 27. P. 4661-4664.
32. Trofimov B. A., SobeninaL. N., Stepanova Z. V. et al. Reactions of 2-phenylpyrrole with bromoben-zoylacetylene on metal oxides active surfaces // Tetrahedron Lett. 2008. Vol. 49. P. 3946.
33. Trofimov A., ChernyakN., GevorgyanV. Dual role of alkynyl halides in one-step synthesis of alkynyl epoxides // J. Am. Chem. Soc. 2008. Vol. 130. P. 5636-5637.
34. BanwellM. G., Goodwin T. E., Ng S. et al. Palladium-catalysed cross-coupling and related reactions involving pyrroles // Eur. J. Org. Chem. 2006. Vol. 31, N 14. P. 3043-3060.
35. Tanaka K. Solvent-free organic synthesis. Weinheim: Wiley-VCH, 2009. 468 p.
Статья поступила в редакцию 26 мая 2014 г.
Контактная информация
Собенина Любовь Николаевна — доктор химических наук.
Трофимов Борис Александрович — академик РАН; e-mail: boris_trofimov@irioch.irk.ru
Sobenina Lyubov' Nikolaevna — Doctor of Chemistry.
Trofimov Boris Aleksandrovich — Academician of Russian Academy of Sciences; e-mail: boris_trofimovCsirioch.irk.ru
