Letter pubs.acs.org/OrgLett
Sonogashira Reaction Using Arylsulfonium Salts as Cross-Coupling Partners Ze-Yu Tian, Shi-Meng Wang, Su-Jiao Jia, Hai-Xia Song, and Cheng-Pan Zhang* School of Chemistry, Chemical Engineering and Life Science, Wuhan University of Technology, 205 Luoshi Road, Wuhan 430070, China S Supporting Information *
ABSTRACT: Triarylsulfonium, alkyl- and fluoroalkyl(diaryl)sulfonium, and aryl(dialkyl)sulfonium triflates are successfully used as a new family of cross-coupling participants in the Sonogashira reaction as aryldiazonium, diaryliodonium, and tetraphenylphosphonium salts. It was found that terminal alkynes reacted mildly with triarylsulfonium or (2,2,2-trifluoroethyl)diphenylsulfonium triflate at room temperature under Pdand Cu-cocatalysis to give the corresponding arylalkynes in up to >99% yield. This protocol represents the first use of arylsulfonium salts as cross-coupling partners in the Pd/Cu-catalyzed Sonogashira reaction. which have been widely applied in the fields of coatings, adhesives, photoresists, microfabrication, and patterning.10 The aryl radicals derived from homolytic reduction of triarylsulfonium salts underwent carbon−carbon bond formation with allyl sulfones and activated olefins.11 Recently, a number of arylsulfonium salts have been explored as powerful arylation reagents in the Pd-catalyzed Suzuki−Miyaura cross-couplings and Mizoroki−Heck reactions.12,13 However, the use of arylsulfonium salts as the cross-coupling participants in the Sonogashira reaction has never been known, despite aryl pseudohalides such as diaryliodonium, aryldiazonium, and arylphosphonium salts having been extensively exploited in this type of reaction.6−8 Furthermore, arylsulfonium salts have featured advantages such as nonvolatility, easy preparation, nontoxicity, and good thermal stability.14,15 We wonder whether arylsulfonium salts can be a new sort of the Sonogashira crosscoupling agents in the presence of Pd- and Cu-catalysts. Indeed, the Pd(PPh3)4-catalyzed reaction of 1-ethynyl-4methoxybenzene 1a with ethyl(diphenyl)sulfonium triflate 2a (1.5 equiv) in DMF in the presence of NEt3 (1 equiv) and 10 mol % CuI at 80 °C for 15 h gave 1-methoxy-4(phenylethynyl)benzene (3a) in 36% yield (Table 1, entry 1). Further investigation showed that Pd[P(t-Bu)3]2 was a better catalyst than Pd(PPh3)4, Pd(PPh3)2Cl2, Pd(OAc)2, Pd2(dba)3, and Pd(PCy3)2, which afforded 3a in 81% yield (Table 1, entries 1−6). Remarkably, using K3PO4 instead of NEt3, the Pd[P(tBu)3]2-catalyzed reaction of 1a and 2a in the presence of 10 mol % of CuI furnished 3a in 96% yield (Table 1, entry 7). Other inorganic bases such as NaHCO3, K2CO3, and K2HPO4 were also amenable in the reaction but provided lower yields of 3a (Table 1, entries 8−10). DMF seemed to be the optimal solvent for the cross-coupling as it performed in other solvents gave 3a in moderate yields (Table 1, entries 11−13). When the catalyst
T
he Sonogashira cross-coupling is a very powerful and convenient reaction for the construction of Csp−Csp2 bonds.1 Over the past few decades, this reaction has become the most important approach to the construction of arylalkynes and conjugated alkenynes, which are essential building blocks in the preparation of natural products, macrocycles, pharmaceuticals, agrochemicals, and functional materials.2 To date, many variations and optimizations have been made on the basis of the original protocol,2−4 in which Heck and Sonogashira first disclosed a Pd- or Pd/Cu-catalyzed reaction of a terminal alkyne with an aryl (or vinyl) halide in the presence of a certain base.3 At present, the substrate scopes of the Sonogashira reaction are significantly expanded. Aryl pseudohalides, such as aryl tosylates, diaryliodonium, and aryldiazonium salts, and tetraphenylphosphonium chloride as well as the complex alkynes have been employed in the Sonogashira cross-coupling with encouraging results (Scheme 1).2c,5−8 Scheme 1. Sonogashira Reactions Using Diaryliodonium, Aryldiazonium, and Tetraphenylphosphonium Salts as the Cross-Coupling Participants
On the other hand, arylsulfonium salts are versatile reagents that have drawn great attention in organic chemistry and materials science in the past several decades.9 They can be readily used as efficient photoinitiators to trigger cationic polymerization or as excellent photoacid generators to produce protons under irradiation through single-electron-transfer processes, © 2017 American Chemical Society
Received: September 5, 2017 Published: September 20, 2017 5454
DOI: 10.1021/acs.orglett.7b02764 Org. Lett. 2017, 19, 5454−5457
Letter
Organic Letters Table 1. Pd/Cu-Catalyzed Cross-Coupling of 1a and 2a
entry
Pd catalyst
base
solvent
3a, yielda (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14c 15d
Pd(PPh3)4 Pd(PPh3)2Cl2 Pd(OAc)2 Pd2(dba)3 Pd(PCy3)2 Pd[P(t-Bu)3]2 Pd[P(t-Bu)3]2 Pd[P(t-Bu)3]2 Pd[P(t-Bu)3]2 Pd[P(t-Bu)3]2 Pd[P(t-Bu)3]2 Pd[P(t-Bu)3]2 Pd[P(t-Bu)3]2 Pd[P(t-Bu)3]2 Pd[P(t-Bu)3]2
Et3N Et3N Et3N Et3N Et3N Et3N K3PO4 NaHCO3 K2CO3 K2HPO4 K3PO4 K3PO4 K3PO4 K3PO4 K3PO4
DMF DMF DMF DMF DMF DMF DMF DMF DMF DMF DMSO 1,4-dioxane toluene DMF DMF
36 68 24 32 30 81 96 (96b) 83 59 58 22 65 59 94 64
Scheme 2. Various Phenylsulfonium Salts as the Sonogashira Cross-Coupling Partnersa
a Reaction conditions: a mixture of 1a (0.2 mmol), phenylsulfonium salt 2 (0.3 mmol), Pd[P(t-Bu)3]2 (10 mol %), CuI (10 mol %), K3PO4 (0.2 mmol), and DMF (2 mL) was reacted in a sealed tube for 15 h. Yields were determined by HPLC using 3a as an external standard (tR = 7.165 min, λmax = 287 nm, H2O/CH3OH = 10:90). bIsolated yield.
a
Reaction conditions: a mixture of 1a (0.2 mmol), 2a (0.3 mmol), CuI (10 mol %), Pd catalyst (10 mol %), K3PO4 (0.2 mmol), and DMF (2 mL) was reacted at 80 °C in a sealed tube for 15 h. Yields were determined by HPLC using 3a as an external standard (tR = 7.165 min, λmax = 287 nm, H2O/CH3OH = 10:90). bIsolated yield. cCuI (7.5 mol %), Pd catalyst (7.5 mol %). dCuI (5 mol %), Pd catalyst (5 mol %).
accordance with the observations that using these salts in the Suzuki−Miyaura and Mizoroki−Heck reactions.12 With the optimized reaction conditions in hand (1/2a or 2e (1.5 equiv)/Pd[P(t-Bu)3]2 (10 mol %)/CuI (10 mol %)/K3PO4 (1.0 equiv)/DMF/80 °C or rt/N2/15 h), the substrate scope of the reaction was examined (Scheme 3). To our delight, various terminal arylethynes 1b−p bearing either electron-donating groups (e.g., methoxy, ethoxy, methyl, and tert-butyl moieties) or electron-withdrawing groups (e.g., cyano, ester, keto, chloro, fluoro, nitro, and formyl groups) on the phenyl rings were all smoothly transformed under the standard conditions to give the
loadings of Pd[P(t-Bu)3]2/CuI were decreased from 10 mol %/10 mol % to 7.5 mol %/7.5 mol %, a comparable yield (94%) of 3a was obtained under the same conditions (Table 1, entry 14). Continuously reducing the catalyst loadings of Pd[P(tBu)3]2/CuI from 7.5 mol %/7.5 mol % to 5 mol %/5 mol % led to 64% of 3a (Table 1, entry 15). The absence of either Pd[P(tBu)3]2 or CuI considerably suppressed the reaction (Table S6), suggesting that an assembly of Pd and Cu catalysts was essential for the high efficiency of the transformation. In addition to 2a, other alkyl(diphenyl)sulfonium salts were studied (Scheme 2). It was found that methyl(diphenyl)sulfonium triflate 2b, diphenyl(propyl)sulfonium triflate 2c, and butyl(diphenyl)sulfonium triflate 2d reacted with 1a in the presence of Pd[P(t-Bu)3]2 (10 mol %), CuI (10 mol %), and K3PO4 (1 equiv) to supply 3a in good yields at 40 or 120 °C (Scheme 2 and Table S7). Triphenylsulfonium triflate 2e appeared to be a more powerful phenylation reagent than alkyl(diphenyl)sulfonium salts, providing >99% of 3a at room temperature. Dialkyl(phenyl)sulfoniums like 2f, 2g, and 2h were also suitable reagents for the reaction, which afforded 3a in 26%, 58%, and 72% yield, respectively, at 80 or 120 °C.16 Diphenyl(trifluoromethyl)sulfonium triflate 2i (the Yaguposkii−Umemoto’s reagent), a prevalent electrophilic CF3 transfer source,17 and previously trifluoromethylating terminal alkyne in the presence of CuI, 2,2′-bipyridine, and K2CO317c yielded 39% or 44% of 3a in this reaction. Diphenyl(2,2,2-trifluoroethyl)sulfonium triflate 2j, a partially fluorinated analogue of 2a, which was successfully applied in trifluoromethyl cyclopropanation of olefins,18 afforded >99% or 93% of 3a in the Pd/Cu-catalyzed reaction with 1a at room temperature or 80 °C. These results suggested that 2j is a very reactive phenylation reagent comparable to 2e in this transformation. Nevertheless, treatment of (perfluoroethyl)diphenylsulfonium triflate 2k or (2,2difluoroethyl)diphenylsulfonium 2l with 1a under the same conditions provided 3a in lower yields. These changes were in
Scheme 3. Sonogashira Reaction of 2a or 2e with Alkynes
a Reaction conditions: a mixture of 1a (0.2 mmol), phenylsulfonium salt 2 (0.3 mmol), Pd[P(t-Bu)3]2 (10 mol %), CuI (10 mol %), K3PO4 (0.2 mmol), and DMF (2 mL) was reacted in a sealed tube for 15 h. Isolated yield. b2e was used instead of 2a at room temperature for 15 h. Isolated yield.
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DOI: 10.1021/acs.orglett.7b02764 Org. Lett. 2017, 19, 5454−5457
Letter
Organic Letters desired phenylation products 3b−p in good to almost quantitative yields. The position of substituent on the aryl segment of arylethyne did not obviously affect the crosscoupling. For instance, reactions of 1-ethynyl-3-methoxybenzene 1b and 1-ethynyl-2-methoxybenzene 1c with 2a at 80 °C afforded 3b and 3c in 86−88% yields, which were comparable to that of 3a from 1a under the same conditions. Alkylalkynes such as but-3-yn-1-ylbenzene 1q, oct-1-yne 1r, and ethynylcyclopropane 1s reacted with 2a or 2e at 80 °C or room temperature to form 3q−s in 42−91% yields. Prop-2-yn-1-yl benzoate 1t and (prop-2-yn-1-yloxy)benzene 1u were also applicable substrates in the reaction, which gave 3t,u in 63−91% yields at room temperature using 2e as a phenylation reagent. Notably, the reaction of unprotected prop-2-yn-1-ol 1v or but-3-yn-2-ol 1w with 2a at 80 °C furnished 3v in 92% yield or 3w in 76% yield. Heteroarylethynes like 3-ethynylthiophene 1x and 3-ethynyl-1tosyl-1H-indole 1y reacted similarly with 2a or 2e to provide 88% of 3x and 80% of 3y, indicating good availability of this method. To further confirm the efficiency and practicality of the reaction, complex molecules like mestranol 1z and erlotinib 1aa were examined under the standard conditions (Scheme 4). Pleasingly,
Table 2. Symmetric and Asymmetric Arylsulfonium Salts as the Cross-Coupling Participantsa
arylsulfonium salt 1
2
2m, Ar = Ar = R = 4-MeC6H4 2n, Ar1 = Ar2 = R = 4-BrC6H4 2o, Ar1 = Ar2 = R = 4-ClC6H4 2p, Ar1 = Ar2 = C6H5, R = 4-MeC6H4 2q, Ar1 = C6H5, Ar2 = 4-MeC6H4, R = 4-BrC6H4 2r, Ar1 = Ar2 = 4-MeC6H4, R= Et 2s, Ar1 = Ar2 = 3,5-(Me)2C6H3, R = Et 2t, Ar1 = C6H5, Ar2 = 4-MeC6H4, R = Et
3, yieldb (%) 3ab (Ar = 4-MeC6H4), 91 3ac (Ar = 4-BrC6H4), 46 3ad (Ar = 4-ClC6H4), 93 3a/3ab = 6.69:1, >99 3a/3ab/3ac = 2.13:1:5.57, 76 3ab, 97 3ae (Ar = 3,5-(Me)2C6H3), 80 3a/3ab = 1.22:1, 87
a
Reaction conditions: a mixture of 1a (0.2 mmol), 2 (0.3 mmol), Pd[P(t-Bu)3]2 (10 mol %), CuI (10 mol %), K3PO4 (0.2 mmol), and DMF (2 mL) was reacted at room temperature (for 2m-q) or 80 °C (for 2r-t) in a sealed tube for 15 h. bIsolated yield. The molar ratio of the product mixtures were determined by 1H NMR spectroscopy.
Scheme 4. Sonogashira Reaction with Complex Alkyne or Sulfonium Salt
sulfonium 2r and bis(3,5-dimethylphenyl)(ethyl)sulfonium 2s reacted with 1a at 80 °C, supplying, respectively, 3ab in 97% yield and 3ae in 80% yield. When the asymmetric ethyl(phenyl)(4tolyl)sulfonium triflate 2t was treated with 1a, a mixture of 3a and 3ab was obtained in 87% yield with a molar ratio of 3a/3ab = 1.22:1, demonstrating again the easier transformation of the phenyl group than the 4-tolyl moiety. In addition, S-(aryl)tetramethylenesulfonium salts have been successfully utilized as arylation reagents in the Pd-catalyzed Suzuki−Miyaura reactions and intramolecular C−S/C-H coupling.13 In our protocol, Sonogashira reaction of ethynylbenzene 1e with 1-(1-tosyl-1H-indol-3-yl)tetrahydro-1H-thiophen-1-ium 2u at 80 °C in the presence of Pd(OAc)2 (10 mol %), CuI (10 mol %), X-Phos (10 mol %), and K3PO4 (1.0 equiv) provided 3y in 82% yield (Scheme 4). The use of a combination of Pd(OAc)2 and X-Phos instead of Pd[P(t-Bu)3]2 facilitated the arylation, giving a better yield of 3y. This example affirmed once again the versatility of arylsulfonium salts as the Sonogashira cross-coupling partners. In conclusion, we have verified that triaryl-, alkyl(diaryl)-, and aryl(dialkyl)sulfonium salts can be used as versatile crosscoupling participants in the Pd/Cu-catalyzed Sonogashira reactions. Various terminal arylethynes and alkylalkynes, including complex bioactive molecules, were smoothly converted under the standard conditions to form the corresponding arylation products in good to almost quantitative yields. Advantages of this reaction include good functional group tolerance, high reactivity, mild conditions, a wide range of crosscoupling reagents, and easy access to the arylsulfonium salts. Since triphenyl-, ethyl(diphenyl)-, and diethyl(phenyl)sulfonium triflates were all effectively transformed in the reaction with alkyne (Scheme 2), each phenyl group of 2e and 2a could be utilized by isolating the thioether byproducts (diphenyl sulfide from 2e and ethylphenyl sulfide from 2a), transferring them to the corresponding arylsulfonium salts (e.g., 2a and 2g), and again phenylating the alkyne. This proposal would improve the atom utilization of triaryl- and diarylsulfonium salts. Moreover, diphenyl(fluoroalkyl)sulfonium triflates are also reliable phenyl-transfer reagents, with 2j being the most powerful one. The asymmetric triarylsulfonium and alkyl(diaryl)sulfonium triflates reacted with alkyne, yielding mixtures of products in which the
reaction of 1z or 1aa with 2a in DMF in the presence of Pd[P(tBu)3]2 (10 mol %), CuI (10 mol %), and K3PO4 (1.0 equiv) at 80 °C for 15 h afforded 3z in 83% yield or 3aa in 75% yield, respectively. Furthermore, symmetric and asymmetric arylsulfonium salts were explored in the Pd/Cu-catalyzed Sonogashira reaction with alkynes. As shown in Table 2, tris(4-tolyl)sulfonium, tris(4bromophenyl)sulfonium, and tris(4-chlorophenyl)sulfonium triflates 2m−o reacted with 1a at room temperature to give 91% of 3ab, 46% of 3ac, and 93% of 3ad. The C−Br bond of 2n was partially retained, and the C−Cl bond of 2o was completely tolerated. Reaction of diphenyl(4-tolyl)sulfonium triflate 2p and 1a under the standard conditions provided a mixture of 3a and 3ab in >99% yield with a molar ratio of 3a/3ab = 6.69:1, which was determined by 1H NMR spectroscopy. This observation hints at a slower transfer of the electron-rich 4-tolyl group than the phenyl moiety in 2p. Similarly, treatment of (4bromophenyl)(phenyl)(4′-tolyl)sulfonium 2q with 1a afforded a mixture of 3a, 3ab, and 3ac in 76% yield with a molar ratio of 3a/3ab/3ac = 2:13:1:5.57, implying that the electron-deficient 4bromophenyl motif was transformed faster than the phenyl group in 2q. Alkyl(diaryl)sulfoniums such as ethyl(di-4-tolyl)5456
DOI: 10.1021/acs.orglett.7b02764 Org. Lett. 2017, 19, 5454−5457
Letter
Organic Letters
W.; Wang, H.; Luo, B.; Hu, Y.; Huang, P.; Wen, S. Chem. - Eur. J. 2015, 21, 18915. (7) Aryldiazonium salts as Sonogashira cross-coupling partners: (a) Panda, B.; Sarkar, T. K. Chem. Commun. 2010, 46, 3131. (b) Fabrizi, G.; Goggiamani, A.; Sferrazza, A.; Cacchi, S. Angew. Chem., Int. Ed. 2010, 49, 4067. (c) Xiao, T.; Dong, X.; Tang, Y.; Zhou, L. Adv. Synth. Catal. 2012, 354, 3195. (d) Barbero, M.; Cadamuro, S.; Dughera, S. Eur. J. Org. Chem. 2014, 2014, 598. (e) Okazaki, T.; Laali, K. K.; Bunge, S. D.; Adas, S. K. Eur. J. Org. Chem. 2014, 2014, 1630. (f) Oger, N.; d’Halluin, M.; Le Grognec, E.; Felpin, F.-X. Org. Process Res. Dev. 2014, 18, 1786. (g) Cai, R.; Lu, M.; Aguilera, E. Y.; Xi, Y.; Akhmedov, N. G.; Petersen, J. L.; Chen, H.; Shi, X. Angew. Chem., Int. Ed. 2015, 54, 8772. (h) TlahuextAca, A.; Hopkinson, M. N.; Sahoo, B.; Glorius, F. Chem. Sci. 2016, 7, 89. (8) [Ph4P]Cl as Sonogashira cross-coupling partner: Hwang, L. K.; Na, Y.; Lee, J.; Do, Y.; Chang, S. Angew. Chem., Int. Ed. 2005, 44, 6166. (9) (a) Crivello, J. V. Adv. Polym. Sci. 1984, 62, 1. (b) Reichmanis, E.; Houlihan, F. M.; Nalamasu, O.; Neenan, T. X. Chem. Mater. 1991, 3, 394. (10) (a) Dektar, J. L.; Hacker, N. P. J. Am. Chem. Soc. 1990, 112, 6004. (b) Crivello, J. V. Radiat. Phys. Chem. 2002, 63, 21. (c) Yi, Y.; Ayothi, R.; Wang, Y.; Li, M.; Barclay, G.; Sierra-Alvarez, R.; Ober, C. K. Chem. Mater. 2009, 21, 4037. (d) Georgiadou, D. G.; Palilis, L. C.; Vasilopoulou, M.; Pistolis, G.; Dimotikali, D.; Argitis, P. J. Mater. Chem. 2011, 21, 9296. (e) Petsalakis, I. D.; Theodorakopoulos, G.; Lathiotakis, N. N.; Georgiadou, D. G.; Vasilopoulou, M.; Argitis, P. Chem. Phys. Lett. 2014, 601, 63. (f) Koefoed, L.; Pedersen, S. U.; Daasbjerg, K. ChemElectroChem 2016, 3, 495. (11) Donck, S.; Baroudi, A.; Fensterbank, L.; Goddard, J.-P.; Ollivier, C. Adv. Synth. Catal. 2013, 355, 1477. (12) (a) Wang, S.-M.; Wang, X.-Y.; Qin, H.-L.; Zhang, C.-P. Chem. Eur. J. 2016, 22, 6542. (b) Wang, S.-M.; Song, H.-X.; Wang, X.-Y.; Liu, N.; Qin, H.-L.; Zhang, C.-P. Chem. Commun. 2016, 52, 11893. (c) Wang, X.-Y.; Song, H.-X.; Wang, S.-M.; Yang, J.; Qin, H.-L.; Jiang, X.; Zhang, C.-P. Tetrahedron 2016, 72, 7606. (13) Nonfluorinated arylsulfonium salts as Suzuki−Miyaura coupling partners: (a) Srogl, J.; Allred, G. D.; Liebeskind, L. S. J. Am. Chem. Soc. 1997, 119, 12376. (b) Vasu, D.; Yorimitsu, H.; Osuka, A. Angew. Chem., Int. Ed. 2015, 54, 7162. (c) Vasu, D.; Yorimitsu, H.; Osuka, A. Synthesis 2015, 47, 3286. (d) Cowper, P.; Jin, Y.; Turton, M. D.; Kociok-Kohn, G.; Lewis, S. E. Angew. Chem., Int. Ed. 2016, 55, 2564. (14) Synthesis of arylsulfonium salts: (a) Miyatake, K.; Yamamoto, K.; Endo, K.; Tsuchida, E. J. Org. Chem. 1998, 63, 7522. (b) Racicot, L.; Kasahara, T.; Ciufolini, M. A. Org. Lett. 2014, 16, 6382. (c) Song, H.-X.; Wang, S.-M.; Wang, X.-Y.; Han, J.-B.; Gao, Y.; Jia, S.-J.; Zhang, C.-P. J. Fluorine Chem. 2016, 192, 131. (15) Miller, R. D.; Renaldo, A. F.; Ito, H. J. Org. Chem. 1988, 53, 5571. (16) Kampmeier, J. A.; Hoque, AKM. M.; Saeva, F. D.; Wedegaertner, D. K.; Thomsen, P.; Ullah, S.; Krake, J.; Lund, T. J. Am. Chem. Soc. 2009, 131, 10015. It was reported that the one-electron reduction of aryl(dialkyl)sulfonium salts never gave S−Caryl bond splitting, whereas reduction of diaryl(alkyl)sulfonium salts preferentially gave S−Caryl bond cleavage. In this Sonogashira reaction, both types of arylsulfonium salts were transformed by S−Caryl bond breakage. (17) (a) Wang, S.-M.; Han, J.-B.; Zhang, C.-P.; Qin, H.-L.; Xiao, J.-C. Tetrahedron 2015, 71, 7949. (b) Hu, X.-Q.; Han, J.-B.; Zhang, C.-P. Eur. J. Org. Chem. 2017, 2017, 324. (c) Wang, X.-P.; Lin, J.-H.; Zhang, C.-P.; Xiao, J.-C.; Zheng, X. Chin. J. Chem. 2013, 31, 915. (18) (a) Duan, Y.; Zhou, B.; Lin, J.-H.; Xiao, J.-C. Chem. Commun. 2015, 51, 13127. (b) Duan, Y.; Lin, J.-H.; Xiao, J.-C.; Gu, Y.-C. Org. Lett. 2016, 18, 2471. (c) Duan, Y.; Lin, J.-H.; Xiao, J.-C.; Gu, Y.-C. Org. Chem. Front. 2017, DOI: 10.1039/C7QO00430C. (d) Hock, K. J.; Hommelsheim, R.; Mertens, L.; Ho, J.; Nguyen, T. V.; Koenigs, R. M. J. Org. Chem. 2017, 82, 8220. (19) Reaction of 1a and 2a in the darkness or with 2.0 equiv of TEMPO under the standard conditions led to few changes in the yield of 3a (Table S5), suggesting that the radical process might not be involved in this conversion.
products with the relatively electron-deficient aryl groups were predominantly formed. This protocol is the first report on the use of arylsulfonium salts as cross-coupling partners in the Pd/Cucatalyzed Sonogashira reaction with alkynes.19 Application of arylsulfonium salts as promising arylation reagents in other transformations is currently underway in our laboratory.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.7b02764. Experimental information, reaction condition optimization, and NMR spectra (PDF)
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AUTHOR INFORMATION
Corresponding Author
* E-mail:
[email protected], zhangchengpan1982@ hotmail.com. ORCID
Cheng-Pan Zhang: 0000-0002-2803-4611 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS C.-P.Z. thanks the Wuhan University of Technology, the Fundamental Research Funds for the Central Universities, the National Natural Science Foundation of China (21602165), the “Chutian Scholar” Program from Department of Education of Hubei Province (China), the “Hundred Talent” Program of Hubei Province, and the Wuhan Youth Chen-Guang Project (2016070204010113) for financial support.
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DEDICATION This work is dedicated to Professor John A. Gladysz at Texas A&M University on the occasion of his 65th birthday.
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REFERENCES
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DOI: 10.1021/acs.orglett.7b02764 Org. Lett. 2017, 19, 5454−5457
