DOI: 10.1002/chem.201406412
Communication
& Hydrothiolation | Hot Paper|
Highly Selective Hydrothiolation of Unsaturated Organosilicon Compounds Catalyzed by Scandium(III) Triflate Krzysztof Kucin´ski,[a] Piotr Pawluc´,[a, b] Bogdan Marciniec,[a, b] and Grzegorz Hreczycho*[a] type addition of thiols to ethynylsilanes is well known. Voronkov and co-workers synthesized a series of thioether-functionalized organosilicon compounds, by use of UV initiation.[19] In contrast to the thiol–ene reaction of allylsilanes, the catalytic methods of thiol–yne reaction of ethynylsilanes also are well known. Sonoda and co-workers reported the hydrothiolation of ethynyltrimethylsilane, catalyzed by Pd(OAc)2.[20] Hydrothiolation reactions of ethynylsilanes in the presence of iridium and rhodium catalysts have also been reported.[21, 22] Recently, we investigated the possibility of using Lewis acids in the synthesis of siloxanes. We discovered the coupling reaction of silanols and silanediols with 2-methylallylsilanes, leading to SiO Si or SiO Ge bond formation with the evolution of isobutylene, catalyzed by Sc(OTf)3.[23, 24] The reactions proceed through catalytic O H bond activation in silanols and cleavage of Si C or Ge C bonds in allylmetalloid molecules. These methods led to the selective synthesis of functionalized di-, triand tetrasiloxanes or germasiloxanes (Scheme 1).
Abstract: The first use of a Lewis acid catalyst in the addition reaction of both aromatic and aliphatic thiols to unsaturated organosilicon compounds is reported. In catalytic tests, scandium(III) triflate demonstrates high catalytic activity in this process. Under mild conditions (25 8C, room temperature, 1–10 h) a number of thioether-functionalized organosilicon species are obtained with appreciable selectivity. This study constitutes the first example of allylsilane hydrothiolation that gives the Markovnikov regioisomer as the main product. Ethynylsilanes are also successfully used in the hydrothiolation reaction in the presence of Sc(OTf)3.
Hydrothiolation reactions allow the introduction of thioether functionality into unsaturated systems.[1–5] Sulfur-containing organosilicon compounds are highly important as reagents and building blocks in complex organic structures such as polymers and dendrimers.[6–8] These compounds are also well known in biology, medicine, and nanotechnology.[9–11] Sulfur-containing organosilicon systems have been used as photoplastic materials,[12] in the treatment of retinal detachment,[13] as superhydrophobic materials,[14] in lithography[15] and in the functionalization of paramagnetic materials.[16] To our knowledge, all earlier research on the addition of thiols to allylsilanes has been based on free-radical reactions.[17] The substrates have been activated by temperature, UV radiation, or free-radical generators, such as organic peroxides or transition metal photocatalysts.[18] The radical-type addition of thiols dominantly leads to the expected anti-Markovnikov compounds.[17] The use of a photoinitiator leads to some disadvantages, for example, the degradation of radical generators caused by sunlight. To avoid the problems related to the use of photoinitiators, initiation by a UV light source has been proposed. Unfortunately, this method is slower and gives lower yields of products. As far as we know, no catalytic method of allylsilane hydrothiolation has yet been reported. The radical-
Scheme 1. Synthesis of linear oligosiloxanes or germasiloxanes catalyzed by Sc(OTf)3.
We decided to investigate the use of Lewis acids derived from triflates for the selective coupling reaction between nonactivated allylsilanes and thiols. Activation of the S H bond in thiols by unsaturated silanes was predicted to occur in the presence of Sc(OTf)3. Unfortunately, formation of the Si S bond was not observed. Instead of Si S coupling, selective hydrothiolation of the unsaturated moiety of the silane (Scheme 2) took place. Similar observations were reported by DuÇach and co-workers, who demonstrated the catalytic func-
[a] K. Kucin´ski, Dr. P. Pawluc´, Prof. Dr. B. Marciniec, Dr. G. Hreczycho Faculty of Chemistry, Adam Mickiewicz University in Poznan´ Umultowska 89b, 61-614 Poznan´ (Poland) E-mail: [email protected] [b] Dr. P. Pawluc´, Prof. Dr. B. Marciniec Center for Advanced Technologies Adam Mickiewicz University in Poznan´ Umultowska 89c, 61-614 Poznan´ (Poland) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201406412. Chem. Eur. J. 2015, 21, 1 – 5
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Communication showed relatively high reactivity in the hydrothiolation reaction catalyzed by Sc(OTf)3 ; however, the reaction required longer time (10 h; Scheme 4). In(OTf)3 was found to be inactive in the addition of aliphatic and aromatic thiols with ethynylsi-
Scheme 2. Sc(OTf)3-catalyzed reaction between allylsilanes and thiols. Scheme 4. The addition of thiols to ethynylsilanes catalyzed by Sc(OTf)3.
tionalization of camphene by sulfur derivatives catalyzed by indium triflate.[25] We initially focused on choosing and testing other catalysts and solvents. As a starting point, the reaction between (2methylallyl)tris(trimethylsiloxy)silane and benzenethiol in the presence of Bi(OTf)3, In(OTf)3, and Sm(OTf)3 was considered. All tests were carried out in the following solvents: Toluene, fluorobenzene, chlorobenzene, acetonitrile, and dichloromethane. Scandium(III) triflate was found to demonstrate the highest activity in hydrothiolation reaction, while toluene and fluorobenzene proved to be the most suitable solvents for this process. Of the other triflates tested, only In(OTf)3 in toluene was found to be an active catalyst, although the reaction proceeded with lower selectivity and required longer time. Subsequently, the nature of substituents attached to the silicon in allylsilanes and to the sulfur in thiols was determined. The nature of substituents of sulfur and silicon atoms proved insignificant for the reaction. Allylsilanes with bulky isopropyl and trimethylsiloxy groups, as well as p-methoxyphenyl group, were chosen as substituents. All of them gave the expected hydrothiolation products in good yields (Table 1, entries 1–11). Most of the thioether-functionalized organosilanes were isolated. The use of allylsilanes in hydrothiolation catalyzed by Sc(OTf)3 led to products consistent with Markovnikov’s rule (Scheme 3).
lanes. Various products of mono- or double-addition reactions were obtained in the presence of Sc(OTf)3, irrespectively of the thiols applied. When the reaction of ethynyltriisopropylsilane with 3-methylbutanethiol in a 1:1 ratio was performed, the mono-addition product was predominantly obtained in the anti-Markovnikov fashion (E/Z = 99:1). However, the mono-addition product was contaminated by double-addition product (mono-/double-addition product ratio = 8:2; Table 1, entry 12). Twofold excess of thiol led exclusively to the double-addition products (Table 1, entries 13–15). Interestingly, catalytic reactions are known to mostly lead to the formation of mono-addition products, consistent with Markovnikov’s rule, whereas radical-type reactions tend to favor the formation of 1,2-double-addition products. However, Prajapati and co-workers reported the reaction between aromatic and aliphatic thiols with alkynes in the presence of In(OTf)3 leading to (E)-vinyl sulfides.[26] We drew similar conclusions. In our study, benzenethiol and 1,3-propanedithiol were used as representative thiols. In the reaction between ethynyltriisopropylsilane and benzenethiol, performed with a 1:2 molar ratio, only the b-dithioacetal was isolated in good yield (70 %; Table 1, entry 13). It is worth noting that the routes to b-dithioacetals that have been proposed so far are very scarce.[27] A more interesting example is the reaction between ethynyltriethyl- or ethynyltriisopropylsilane with 1,3-propanedithiol. When ethynyltriethylsilane was used, two types of products were observed; 1,2- and 2,2-double-addition products. Firstly, one of the SH groups in 1,3-propanedithiol underwent addition to the carbon–carbon triple bond. After that, the second SH group could be involved in two alternative addition reactions (Scheme 5). It could lead to the cyclic 1,2- or 2,2-doubleaddition products (Table 1, entry 15). In the case of hydrothiolation of ethynyltriisopropylsilane by 1,3-propanedithiol (Table 1, entry 14), only b-dithioacetal was obtained (Scheme 5). This outcome is interpreted as a result of the steric hindrance of bulky isopropyl groups, which prevented the formation of the 1,2-double-addition product. In conclusion, we have reported the highly selective hydrothiolation of unsaturated organosilicon compounds by both aromatic and aliphatic thiols in the presence of Sc(OTf)3. The use of allylsilanes led to products that are consistent with Markov-
Scheme 3. The addition of thiols to allylsilanes catalyzed by Sc(OTf)3.
All thiol–ene reactions that occur according to the radical mechanism have yielded the anti-Markovnikov regioisomer. Therefore, each product obtained in these reactions through allylsilane hydrothiolation was classified as a novel thioetherfunctionalized silane. Ethynylsilanes were also investigated as substrates for Sc(OTf)3-catalyzed hydrothiolation. These compounds, represented by ethynyltriethylsilane and ethynyltriisopropylsilane, &
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Communication Table 1. The products of Sc(OTf)3-catalyzed addition of aromatic and aliphatic thiols to allyl- and ethynylsilanes.[a] Entry Silane
Thiol
Silane/thiol molar ratio Yield[b] (isolated) [%]
Product
1
1
1:2
90 (85)
2
2
1:2
90 (82)
3
3
1:2
98 (95)
4
4
1:2
97 (95)
5
5
1:2
98 (95)
6
6
1:2
85 (78)
7
7
1:2
90 (86)
8
8
1:2
84 (75)
9
9
1:2
93 (90)
10
10
1:6
90 (85)
11
11
1:2
80 (70)
1:1
89 (70) [12]/[13] = 8:2[b]
12
13
14
1:2
78 (70)
14
15
1:1
75 (68)
1:1
73 (67) [16]/[17] = 51:49[b]
15
[a] Reaction conditions: toluene, room temperature, 1 h (entries 1–11) or 10 h (entries 12–15); catalyst loading, 2 mol %. [b] Measured by GC.
Scheme 5. Potential products of the addition reaction between 1,3-propanedithiol and ethynyltriethyl- or ethynyltriisopropylsilane. Chem. Eur. J. 2015, 21, 1 – 5
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Communication Acknowledgements
nikov’s rule. The application of ethynylsilanes led to the formation of double-addition products—mostly b-dithioacetals. The reaction occurred via (E)-vinyl sulfide intermediates. Substituents at the silicon atom had a great effect on the structure of the final product when 1,3-propanedithiol was used. Steric hindrance from bulky isopropyl groups, in contrast to ethyl groups, led to the formation of only the 2,2-double addition cyclic product. The majority of reports on hydrothiolation chemistry in recent years have detailed its application in modifying polymers and the synthesis of dendrimers. Currently, we are working on expanding our method to multi-unsaturated organosilicon compounds.
This work was supported by National Science Centre Grant No. UMO-2013/09/B/ST5/00293. Keywords: allylic compounds · hydrothiolation · Lewis acids · scandium · silanes [1] C. E. Hoyle, C. N. Bowman, Angew. Chem. Int. Ed. 2010, 49, 1540 – 1573; Angew. Chem. 2010, 122, 1584 – 1617. [2] R. Castarlenas, A. Di Giuseppe, J. J. Perez-Torrente, L. A. Oro, Angew. Chem. Int. Ed. 2013, 52, 211 – 222; Angew. Chem. 2013, 125, 223 – 234. [3] A. B. Lowe, Polymer 2014, 55, 5517 – 5549. [4] C. C. Silveira, S. R. Mendes, F. M. Libero, Synlett 2010, 5, 790 – 792. [5] A. B. Lowe, Polym. Chem. 2014, 5, 4820 – 4870. [6] C. Kuttner, P. C. Maier, C. Kunert, H. Schlaad, A. Fery, Langmuir 2013, 29, 16119 – 16126. [7] L. Ding, T. Hayakawa, M. A. Kakimoto, Polym. J. 2007, 39, 551 – 557. [8] C. Rissing, D. Y. Son, Organometallics 2009, 28, 3167 – 3172. [9] D. B. Cordes, P. D. Lickiss, F. Rataboul, Chem. Rev. 2010, 110, 2081 – 2173. [10] J. Zhang, Y. Chen, M. A. Brook, Langmuir 2013, 29, 12432 – 12442. [11] H. Yang, M. Liu, Y. Yao, P. Tao, B. Lin, P. Keller, X. Zhang, Y. Sun, L. Guo, Macromolecules 2013, 46, 3406 – 3416. [12] S. N. Pawar, T. W. Smith, Abstr. Pap. Am. Chem. S. 2008, 235, 474-POLY. [13] O. T. Mefford, R. C. Woodward, J. D. Goff, T. P. Vadala, T. G. St. Pierre, J. P. Dailey, J. S. Riffle, J. Magn. Magn. Mater. 2007, 311, 347 – 353. [14] B. J. Sparks, E. F. T. Hoff, L. Xiong, J. T. Goetz, D. L. Patton, ACS Appl. Mater. Interfaces 2013, 5, 1811 – 1817. [15] L. M. Campos, T. T. Truong, D. E. Shim, M. D. Dimitriou, D. Shir, I. Meinel, J. A. Gerbec, H. T. Hahn, J. A. Rogers, C. J. Hawker, Chem. Mater. 2009, 21, 5319 – 5326. [16] A. K. Tucker-Schwartz, R. A. Farrell, R. L. Garrell, J. Am. Chem. Soc. 2011, 133, 11026 – 11029. [17] Ch. Rissing, D. Y. Son, Main Group Chem. 2009, 8, 251 – 262. [18] E. L. Tyson, M. S. Ament, T. P. Yoon, J. Org. Chem. 2013, 78, 2046 – 2050. [19] a) M. G. Voronkov, V. I. Rakhlin, R. G. Mirskov, S. K. Khangazheev, O. G. Yarosh, E. O. Tsetlina, Zh. Obshch. Khim. 1979, 49, 119 – 126; b) M. G. Voronkov, N. N. Vlasova, G. Yu. Zhila, E. I. Brodskaya, O. G. Yarosh, V. Yu. Vitkovskii, Zh. Obshch. Khim. 1990, 60, 855 – 861. [20] H. Kuniyasu, A. Ogawa, K. Sato, I. Ryu, N. Kambe, N. Sonoda, J. Am. Chem. Soc. 1992, 114, 5902 – 5903. [21] S. Burling, L. D. Field, B. A. Messerle, K. Q. Vuong, P. Turner, Dalton Trans. 2003, 4181 – 4191. [22] J. Yang, A. Sabarre, L. R. Fraser, B. O. Patrick, J. A. Love, J. Org. Chem. 2009, 74, 182 – 187. [23] G. Hreczycho, P. Pawluc´, B. Marciniec, New J. Chem. 2011, 35, 2743 – 2746. [24] G. Hreczycho, K. Kucin´ski, P. Pawluc´, B. Marciniec, Organometallics 2013, 32, 5001 – 5004. [25] M. Weı¨wer, X. Chaminade, J. C. Bayn, E. DuÇach, Eur. J. Org. Chem. 2007, 2464 – 2469. [26] R. Sarma, N. Rajesh, D. Prajapati, Chem. Commun. 2012, 48, 4014 – 4016. [27] M. Hut’ka, T. Tsubogo, S. Kobayashi, Organometallics 2014, 33, 5626 – 5629.
Experimental Section General procedures The reagents and Sc(OTf)3 used for experiments were purchased from Sigma–Aldrich Co. and ABCR GmbH & Co. KG and used without further purification. 1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were recorded on a Varian XL 300 spectrometer using C6D6 as a solvent. GC analyses were performed on a Varian 3400 with a Megabore column (30 m) and TCD. Mass spectra of the products were determined by GC-MS analysis on a Varian Saturn 2100T, equipped with a BD-5 capillary column (30 m) and a Finnigan Mat 800 ion trap detector.
Hydrothiolation of allylsilanes In a 25 mL one-necked round-bottom flask, toluene (3 mL), allylsilane (0.7 mmol), thiol (1.4 mmol), and Sc(OTf)3 (0.014 mmol; 6.9 mg) were added. The reaction mixture was stirred at room temperature for 1 h. The progress of the reaction was monitored by GC and GC-MS analyses. After the reaction was complete, all volatiles were removed under reduced pressure. The crude product was purified by column chromatography on silica gel eluting with n-hexane to give the corresponding compounds 1–11.
Hydrothiolation of ethynylsilanes In a 25 mL one-necked round-bottom flask, toluene (5 mL), ethynylsilane (2.2 mmol), thiol (2.2 or 4.4 mmol), and Sc(OTf)3 (0.044 mmol, 0.022 g) were added. The reaction mixture was stirred at room temperature for 10 h. The progress of the reaction was monitored by GC and GC-MS analyses. After the reaction was complete, all volatiles were removed under reduced pressure. The crude product was distilled by “trap-to-trap” technique at reduced pressure, to give the corresponding compounds 12–17.
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Communication
COMMUNICATION & Hydrothiolation K. Kucin´ski, P. Pawluc´, B. Marciniec, G. Hreczycho* Stick to the rules: The use of Lewis acid as a catalyst in the addition of thiols to unsaturated organosilicon compounds is reported. Scandium(III) triflate demonstrates high catalytic activity in this process. The use of allylsi-
Chem. Eur. J. 2015, 21, 1 – 5
lanes leads to products that are consistent with the Markovnikov’s rule. This is the first example of allylsilane hydrothiolation that gives the Markovnikov regioisomer as the main product.
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&& – && Highly Selective Hydrothiolation of Unsaturated Organosilicon Compounds Catalyzed by Scandium(III) Triflate
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Communication
& Hydrothiolation | Hot Paper|
Highly Selective Hydrothiolation of Unsaturated Organosilicon Compounds Catalyzed by Scandium(III) Triflate Krzysztof Kucin´ski,[a] Piotr Pawluc´,[a, b] Bogdan Marciniec,[a, b] and Grzegorz Hreczycho*[a] type addition of thiols to ethynylsilanes is well known. Voronkov and co-workers synthesized a series of thioether-functionalized organosilicon compounds, by use of UV initiation.[19] In contrast to the thiol–ene reaction of allylsilanes, the catalytic methods of thiol–yne reaction of ethynylsilanes also are well known. Sonoda and co-workers reported the hydrothiolation of ethynyltrimethylsilane, catalyzed by Pd(OAc)2.[20] Hydrothiolation reactions of ethynylsilanes in the presence of iridium and rhodium catalysts have also been reported.[21, 22] Recently, we investigated the possibility of using Lewis acids in the synthesis of siloxanes. We discovered the coupling reaction of silanols and silanediols with 2-methylallylsilanes, leading to SiO Si or SiO Ge bond formation with the evolution of isobutylene, catalyzed by Sc(OTf)3.[23, 24] The reactions proceed through catalytic O H bond activation in silanols and cleavage of Si C or Ge C bonds in allylmetalloid molecules. These methods led to the selective synthesis of functionalized di-, triand tetrasiloxanes or germasiloxanes (Scheme 1).
Abstract: The first use of a Lewis acid catalyst in the addition reaction of both aromatic and aliphatic thiols to unsaturated organosilicon compounds is reported. In catalytic tests, scandium(III) triflate demonstrates high catalytic activity in this process. Under mild conditions (25 8C, room temperature, 1–10 h) a number of thioether-functionalized organosilicon species are obtained with appreciable selectivity. This study constitutes the first example of allylsilane hydrothiolation that gives the Markovnikov regioisomer as the main product. Ethynylsilanes are also successfully used in the hydrothiolation reaction in the presence of Sc(OTf)3.
Hydrothiolation reactions allow the introduction of thioether functionality into unsaturated systems.[1–5] Sulfur-containing organosilicon compounds are highly important as reagents and building blocks in complex organic structures such as polymers and dendrimers.[6–8] These compounds are also well known in biology, medicine, and nanotechnology.[9–11] Sulfur-containing organosilicon systems have been used as photoplastic materials,[12] in the treatment of retinal detachment,[13] as superhydrophobic materials,[14] in lithography[15] and in the functionalization of paramagnetic materials.[16] To our knowledge, all earlier research on the addition of thiols to allylsilanes has been based on free-radical reactions.[17] The substrates have been activated by temperature, UV radiation, or free-radical generators, such as organic peroxides or transition metal photocatalysts.[18] The radical-type addition of thiols dominantly leads to the expected anti-Markovnikov compounds.[17] The use of a photoinitiator leads to some disadvantages, for example, the degradation of radical generators caused by sunlight. To avoid the problems related to the use of photoinitiators, initiation by a UV light source has been proposed. Unfortunately, this method is slower and gives lower yields of products. As far as we know, no catalytic method of allylsilane hydrothiolation has yet been reported. The radical-
Scheme 1. Synthesis of linear oligosiloxanes or germasiloxanes catalyzed by Sc(OTf)3.
We decided to investigate the use of Lewis acids derived from triflates for the selective coupling reaction between nonactivated allylsilanes and thiols. Activation of the S H bond in thiols by unsaturated silanes was predicted to occur in the presence of Sc(OTf)3. Unfortunately, formation of the Si S bond was not observed. Instead of Si S coupling, selective hydrothiolation of the unsaturated moiety of the silane (Scheme 2) took place. Similar observations were reported by DuÇach and co-workers, who demonstrated the catalytic func-
[a] K. Kucin´ski, Dr. P. Pawluc´, Prof. Dr. B. Marciniec, Dr. G. Hreczycho Faculty of Chemistry, Adam Mickiewicz University in Poznan´ Umultowska 89b, 61-614 Poznan´ (Poland) E-mail: [email protected] [b] Dr. P. Pawluc´, Prof. Dr. B. Marciniec Center for Advanced Technologies Adam Mickiewicz University in Poznan´ Umultowska 89c, 61-614 Poznan´ (Poland) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201406412. Chem. Eur. J. 2015, 21, 1 – 5
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Communication showed relatively high reactivity in the hydrothiolation reaction catalyzed by Sc(OTf)3 ; however, the reaction required longer time (10 h; Scheme 4). In(OTf)3 was found to be inactive in the addition of aliphatic and aromatic thiols with ethynylsi-
Scheme 2. Sc(OTf)3-catalyzed reaction between allylsilanes and thiols. Scheme 4. The addition of thiols to ethynylsilanes catalyzed by Sc(OTf)3.
tionalization of camphene by sulfur derivatives catalyzed by indium triflate.[25] We initially focused on choosing and testing other catalysts and solvents. As a starting point, the reaction between (2methylallyl)tris(trimethylsiloxy)silane and benzenethiol in the presence of Bi(OTf)3, In(OTf)3, and Sm(OTf)3 was considered. All tests were carried out in the following solvents: Toluene, fluorobenzene, chlorobenzene, acetonitrile, and dichloromethane. Scandium(III) triflate was found to demonstrate the highest activity in hydrothiolation reaction, while toluene and fluorobenzene proved to be the most suitable solvents for this process. Of the other triflates tested, only In(OTf)3 in toluene was found to be an active catalyst, although the reaction proceeded with lower selectivity and required longer time. Subsequently, the nature of substituents attached to the silicon in allylsilanes and to the sulfur in thiols was determined. The nature of substituents of sulfur and silicon atoms proved insignificant for the reaction. Allylsilanes with bulky isopropyl and trimethylsiloxy groups, as well as p-methoxyphenyl group, were chosen as substituents. All of them gave the expected hydrothiolation products in good yields (Table 1, entries 1–11). Most of the thioether-functionalized organosilanes were isolated. The use of allylsilanes in hydrothiolation catalyzed by Sc(OTf)3 led to products consistent with Markovnikov’s rule (Scheme 3).
lanes. Various products of mono- or double-addition reactions were obtained in the presence of Sc(OTf)3, irrespectively of the thiols applied. When the reaction of ethynyltriisopropylsilane with 3-methylbutanethiol in a 1:1 ratio was performed, the mono-addition product was predominantly obtained in the anti-Markovnikov fashion (E/Z = 99:1). However, the mono-addition product was contaminated by double-addition product (mono-/double-addition product ratio = 8:2; Table 1, entry 12). Twofold excess of thiol led exclusively to the double-addition products (Table 1, entries 13–15). Interestingly, catalytic reactions are known to mostly lead to the formation of mono-addition products, consistent with Markovnikov’s rule, whereas radical-type reactions tend to favor the formation of 1,2-double-addition products. However, Prajapati and co-workers reported the reaction between aromatic and aliphatic thiols with alkynes in the presence of In(OTf)3 leading to (E)-vinyl sulfides.[26] We drew similar conclusions. In our study, benzenethiol and 1,3-propanedithiol were used as representative thiols. In the reaction between ethynyltriisopropylsilane and benzenethiol, performed with a 1:2 molar ratio, only the b-dithioacetal was isolated in good yield (70 %; Table 1, entry 13). It is worth noting that the routes to b-dithioacetals that have been proposed so far are very scarce.[27] A more interesting example is the reaction between ethynyltriethyl- or ethynyltriisopropylsilane with 1,3-propanedithiol. When ethynyltriethylsilane was used, two types of products were observed; 1,2- and 2,2-double-addition products. Firstly, one of the SH groups in 1,3-propanedithiol underwent addition to the carbon–carbon triple bond. After that, the second SH group could be involved in two alternative addition reactions (Scheme 5). It could lead to the cyclic 1,2- or 2,2-doubleaddition products (Table 1, entry 15). In the case of hydrothiolation of ethynyltriisopropylsilane by 1,3-propanedithiol (Table 1, entry 14), only b-dithioacetal was obtained (Scheme 5). This outcome is interpreted as a result of the steric hindrance of bulky isopropyl groups, which prevented the formation of the 1,2-double-addition product. In conclusion, we have reported the highly selective hydrothiolation of unsaturated organosilicon compounds by both aromatic and aliphatic thiols in the presence of Sc(OTf)3. The use of allylsilanes led to products that are consistent with Markov-
Scheme 3. The addition of thiols to allylsilanes catalyzed by Sc(OTf)3.
All thiol–ene reactions that occur according to the radical mechanism have yielded the anti-Markovnikov regioisomer. Therefore, each product obtained in these reactions through allylsilane hydrothiolation was classified as a novel thioetherfunctionalized silane. Ethynylsilanes were also investigated as substrates for Sc(OTf)3-catalyzed hydrothiolation. These compounds, represented by ethynyltriethylsilane and ethynyltriisopropylsilane, &
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Communication Table 1. The products of Sc(OTf)3-catalyzed addition of aromatic and aliphatic thiols to allyl- and ethynylsilanes.[a] Entry Silane
Thiol
Silane/thiol molar ratio Yield[b] (isolated) [%]
Product
1
1
1:2
90 (85)
2
2
1:2
90 (82)
3
3
1:2
98 (95)
4
4
1:2
97 (95)
5
5
1:2
98 (95)
6
6
1:2
85 (78)
7
7
1:2
90 (86)
8
8
1:2
84 (75)
9
9
1:2
93 (90)
10
10
1:6
90 (85)
11
11
1:2
80 (70)
1:1
89 (70) [12]/[13] = 8:2[b]
12
13
14
1:2
78 (70)
14
15
1:1
75 (68)
1:1
73 (67) [16]/[17] = 51:49[b]
15
[a] Reaction conditions: toluene, room temperature, 1 h (entries 1–11) or 10 h (entries 12–15); catalyst loading, 2 mol %. [b] Measured by GC.
Scheme 5. Potential products of the addition reaction between 1,3-propanedithiol and ethynyltriethyl- or ethynyltriisopropylsilane. Chem. Eur. J. 2015, 21, 1 – 5
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Communication Acknowledgements
nikov’s rule. The application of ethynylsilanes led to the formation of double-addition products—mostly b-dithioacetals. The reaction occurred via (E)-vinyl sulfide intermediates. Substituents at the silicon atom had a great effect on the structure of the final product when 1,3-propanedithiol was used. Steric hindrance from bulky isopropyl groups, in contrast to ethyl groups, led to the formation of only the 2,2-double addition cyclic product. The majority of reports on hydrothiolation chemistry in recent years have detailed its application in modifying polymers and the synthesis of dendrimers. Currently, we are working on expanding our method to multi-unsaturated organosilicon compounds.
This work was supported by National Science Centre Grant No. UMO-2013/09/B/ST5/00293. Keywords: allylic compounds · hydrothiolation · Lewis acids · scandium · silanes [1] C. E. Hoyle, C. N. Bowman, Angew. Chem. Int. Ed. 2010, 49, 1540 – 1573; Angew. Chem. 2010, 122, 1584 – 1617. [2] R. Castarlenas, A. Di Giuseppe, J. J. Perez-Torrente, L. A. Oro, Angew. Chem. Int. Ed. 2013, 52, 211 – 222; Angew. Chem. 2013, 125, 223 – 234. [3] A. B. Lowe, Polymer 2014, 55, 5517 – 5549. [4] C. C. Silveira, S. R. Mendes, F. M. Libero, Synlett 2010, 5, 790 – 792. [5] A. B. Lowe, Polym. Chem. 2014, 5, 4820 – 4870. [6] C. Kuttner, P. C. Maier, C. Kunert, H. Schlaad, A. Fery, Langmuir 2013, 29, 16119 – 16126. [7] L. Ding, T. Hayakawa, M. A. Kakimoto, Polym. J. 2007, 39, 551 – 557. [8] C. Rissing, D. Y. Son, Organometallics 2009, 28, 3167 – 3172. [9] D. B. Cordes, P. D. Lickiss, F. Rataboul, Chem. Rev. 2010, 110, 2081 – 2173. [10] J. Zhang, Y. Chen, M. A. Brook, Langmuir 2013, 29, 12432 – 12442. [11] H. Yang, M. Liu, Y. Yao, P. Tao, B. Lin, P. Keller, X. Zhang, Y. Sun, L. Guo, Macromolecules 2013, 46, 3406 – 3416. [12] S. N. Pawar, T. W. Smith, Abstr. Pap. Am. Chem. S. 2008, 235, 474-POLY. [13] O. T. Mefford, R. C. Woodward, J. D. Goff, T. P. Vadala, T. G. St. Pierre, J. P. Dailey, J. S. Riffle, J. Magn. Magn. Mater. 2007, 311, 347 – 353. [14] B. J. Sparks, E. F. T. Hoff, L. Xiong, J. T. Goetz, D. L. Patton, ACS Appl. Mater. Interfaces 2013, 5, 1811 – 1817. [15] L. M. Campos, T. T. Truong, D. E. Shim, M. D. Dimitriou, D. Shir, I. Meinel, J. A. Gerbec, H. T. Hahn, J. A. Rogers, C. J. Hawker, Chem. Mater. 2009, 21, 5319 – 5326. [16] A. K. Tucker-Schwartz, R. A. Farrell, R. L. Garrell, J. Am. Chem. Soc. 2011, 133, 11026 – 11029. [17] Ch. Rissing, D. Y. Son, Main Group Chem. 2009, 8, 251 – 262. [18] E. L. Tyson, M. S. Ament, T. P. Yoon, J. Org. Chem. 2013, 78, 2046 – 2050. [19] a) M. G. Voronkov, V. I. Rakhlin, R. G. Mirskov, S. K. Khangazheev, O. G. Yarosh, E. O. Tsetlina, Zh. Obshch. Khim. 1979, 49, 119 – 126; b) M. G. Voronkov, N. N. Vlasova, G. Yu. Zhila, E. I. Brodskaya, O. G. Yarosh, V. Yu. Vitkovskii, Zh. Obshch. Khim. 1990, 60, 855 – 861. [20] H. Kuniyasu, A. Ogawa, K. Sato, I. Ryu, N. Kambe, N. Sonoda, J. Am. Chem. Soc. 1992, 114, 5902 – 5903. [21] S. Burling, L. D. Field, B. A. Messerle, K. Q. Vuong, P. Turner, Dalton Trans. 2003, 4181 – 4191. [22] J. Yang, A. Sabarre, L. R. Fraser, B. O. Patrick, J. A. Love, J. Org. Chem. 2009, 74, 182 – 187. [23] G. Hreczycho, P. Pawluc´, B. Marciniec, New J. Chem. 2011, 35, 2743 – 2746. [24] G. Hreczycho, K. Kucin´ski, P. Pawluc´, B. Marciniec, Organometallics 2013, 32, 5001 – 5004. [25] M. Weı¨wer, X. Chaminade, J. C. Bayn, E. DuÇach, Eur. J. Org. Chem. 2007, 2464 – 2469. [26] R. Sarma, N. Rajesh, D. Prajapati, Chem. Commun. 2012, 48, 4014 – 4016. [27] M. Hut’ka, T. Tsubogo, S. Kobayashi, Organometallics 2014, 33, 5626 – 5629.
Experimental Section General procedures The reagents and Sc(OTf)3 used for experiments were purchased from Sigma–Aldrich Co. and ABCR GmbH & Co. KG and used without further purification. 1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were recorded on a Varian XL 300 spectrometer using C6D6 as a solvent. GC analyses were performed on a Varian 3400 with a Megabore column (30 m) and TCD. Mass spectra of the products were determined by GC-MS analysis on a Varian Saturn 2100T, equipped with a BD-5 capillary column (30 m) and a Finnigan Mat 800 ion trap detector.
Hydrothiolation of allylsilanes In a 25 mL one-necked round-bottom flask, toluene (3 mL), allylsilane (0.7 mmol), thiol (1.4 mmol), and Sc(OTf)3 (0.014 mmol; 6.9 mg) were added. The reaction mixture was stirred at room temperature for 1 h. The progress of the reaction was monitored by GC and GC-MS analyses. After the reaction was complete, all volatiles were removed under reduced pressure. The crude product was purified by column chromatography on silica gel eluting with n-hexane to give the corresponding compounds 1–11.
Hydrothiolation of ethynylsilanes In a 25 mL one-necked round-bottom flask, toluene (5 mL), ethynylsilane (2.2 mmol), thiol (2.2 or 4.4 mmol), and Sc(OTf)3 (0.044 mmol, 0.022 g) were added. The reaction mixture was stirred at room temperature for 10 h. The progress of the reaction was monitored by GC and GC-MS analyses. After the reaction was complete, all volatiles were removed under reduced pressure. The crude product was distilled by “trap-to-trap” technique at reduced pressure, to give the corresponding compounds 12–17.
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Chem. Eur. J. 2015, 21, 1 – 5
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Received: December 9, 2014 Published online on && &&, 0000
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Communication
COMMUNICATION & Hydrothiolation K. Kucin´ski, P. Pawluc´, B. Marciniec, G. Hreczycho* Stick to the rules: The use of Lewis acid as a catalyst in the addition of thiols to unsaturated organosilicon compounds is reported. Scandium(III) triflate demonstrates high catalytic activity in this process. The use of allylsi-
Chem. Eur. J. 2015, 21, 1 – 5
lanes leads to products that are consistent with the Markovnikov’s rule. This is the first example of allylsilane hydrothiolation that gives the Markovnikov regioisomer as the main product.
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&& – && Highly Selective Hydrothiolation of Unsaturated Organosilicon Compounds Catalyzed by Scandium(III) Triflate
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