Subscriber access provided by UNIV OF CAMBRIDGE
Letter
Nickel-Catalyzed C-H Alkynylation of Anilines: Expedient Access to Functionalized Indoles and Purine Nucleobases Zhixiong Ruan, Sebastian Lackner, and Lutz Ackermann ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b01120 • Publication Date (Web): 16 Jun 2016 Downloaded from http://pubs.acs.org on June 16, 2016
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
Nickel-Catalyzed C−H Alkynylation of Anilines: Expedient Access to Functionalized Indoles and Purine Nucleobases Zhixiong Ruan,a Sebastian Lackner,a and Lutz Ackermanna,b* a
Institut für Organische und Biomolekulare Chemie, Georg-August-Universität, Tammannstraße 2, 37077 Göttingen, Germany
b
Department of Chemistry, University of Pavia, Viale Taramelli 10, 27100 Pavia, Italy
Supporting Information Placeholder ABSTRACT: C–H alkynylations of electron-rich anilines were accomplished by means of user-friendly nickel catalysis. The C–H functionalization occurred with high positional selectivity and ample scope by kinetically relevant C–H activation. The robust nickel catalyst tolerated synthetically useful functional groups, which set the stage for the facile synthesis of substituted indoles. The chemo-selectivity of the cost-effective nickel catalyst was reflected by enabling transformative nickel-catalyzed C–H functionalization with purine nucleobases through mono-dentate chelation assistance.
KEYWORDS: alkynylation, C–H activation, indoles, nickel, nucleobases, purines The direct functionalization of otherwise inert C–H bonds has emerged as an enabling technology,1 with applications to material sciences,2 pharmaceutical industries3 and natural product chemistry,4 among others. Particularly, C–H alkynylations have been identified as increasingly powerful alternatives to the palladiumcatalyzed Sonogashira-Hagihara reaction.5 The vast majority of these C–H alkynylations was accomplished with precious 4d and 5d transition metal catalysts.6 In the recent years, focus in C–H activation chemistry has shifted towards the use of naturally abundant base metal catalysts,7 with significant progress in nickel-catalyzed8 C–H alkynylations.9 In spite of undisputable advances,8,9 all nickel-catalyzed C–H alkynylations were limited to benzamide substrates bearing N,N-bidentate auxiliaries (Figure 1a), thus, significantly restricting the approach to inherently electron-deficient benzoic acid derivatives. Within our own program on nickel-catalyzed C–H activation,10 we have now developed a first protocol for nickelcatalyzed C–H alkynylations of electron-rich aniline derivatives, on which we report herein. Notable features of our findings include the use of inexpensive nickel(II) catalysts for C–H alkynylations of synthetically meaningful anilines displaying mono-dentate pyrimidines. Indeed, our C–H alkynylation strategy set the stage for a novel step-economical indole11 synthesis, and enabled the first nickel-catalyzed C–H functionalizations on purine nucleobases (Figure 1b).12
Figure 1. Nickel-Catalyzed C–H Alkynylation of Anilines.
We initiated our studies by probing a representative set of nickel sources for the desired C–H alkynylation of the 2-pyrimidyl (pym) substituted aniline 1a with alkyne 2a (Table 1, and Table S1 in the Supporting Information).13 Thus, the user-friendly complex (DME)NiCl2 proved to be highly effective (entries 1–5), while the C–H transformation failed to occur in the absence of a nickel complex (entry 1). Among a variety of ligands, DtBEDA (4) was identified as being optimal (entries 6–10), thereby leading to a significantly reduced catalyst loading (entry 11). The conversion of substrate 1 was not achieved with Na2CO3, K2CO3 and LiHMDS as the base, while KOt-Bu gave only trace amounts of the desired product 3aa. It is noteworthy that the C–H functionalization did proceed in the
ACS Paragon Plus Environment
ACS Catalysis
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
absence of an additional ligand likewise, albeit with somewhat reduced efficacy (entry 10).
Page 2 of 5
Scheme 1. Scope of C–H Alkynylation of Anilines 1. Isolated yields of the dialkynylated products 3’.
[a]
Table 1. Nickel-Catalyzed C–H Alkynylation of Aniline 1a Me
H N H
N N
TIPS
H N
+ Br
1a
entry 1
Me
cat. [Ni] cat. ligand LiOt-Bu 1,4-dioxane T, 16 h
2a
2-pym
t-Bu NH HN t-Bu DtBEDA 4
TIPS 3aa
[Ni] ---
ligand DtBEDA (4)
T [°C] 100
3aa [%] 0 61
2
(DME)NiCl2
DtBEDA (4)
100
3
Ni(acac)2
DtBEDA (4)
100
53
4
Ni(OTf)2
DtBEDA (4)
100
51
5
Ni(cod)2
PPh3
100
46
6
(DME)NiCl2
DtBEDA (4)
85
56
7
(DME)NiCl2
DtBEDA (4)
120
53
8
(DME)NiCl2
BINOL
100
45
9
(DME)NiCl2
PPh3
100
60
10
(DME)NiCl2
---
100
53
(DME)NiCl2
DtBEDA (4)
100
68b
11 a
Reaction conditions: 1a (0.5 mmol), 2a (2.0 equiv), [Ni] (10 mol %), ligand (20 mol %), LiOt-Bu (2.0 equiv), 1,4-dioxane (1.5 mL), 16 h. b 1a (0.5 mmol), 2a (3.0 equiv), [Ni] (2.5 mol %), LiOt-Bu (2.0 equiv), ligand (5.0 mol %), 100 °C, 16 h. pym = pyrimidin-2-yl. .
Subsequently, we explored the versatility of the nickelcatalyzed C–H alkynylation protocol by probing diversely decorated anilines 1 (Scheme 1). Hence, the optimized catalytic system proved widely applicable and enabled the C–H functionalization with unsubstituted as well as paraand ortho-substituted anilines 1b–1i with high efficacy and chemo-selectivity. C–H alkynylations with metasubstituted arenes 1j–1q occurred at the sterically less encumbered C–H bond with excellent levels of positional control. The robustness of the versatile nickel catalyst was inter alia reflected by fully tolerating valuable electrophilic functional groups, including chloro, bromo, ketone, ester or amino substituents (3ma–3qa). Furthermore, the heterocyclic substrate 1r provided the desired product 3ra with high levels of regio control. It is noteworthy that the corresponding N-pyridin-2-yl-substituted aniline as well as the pyrimidin-2-yl-substituted phenol failed to undergo the C–H alkynylation, highlighting the unique features of the deprotonable pyrimidyl aniline motif.
Moreover, the nickel catalyst derived from ligand 4 proved amenable to the C–H transformation with different alkynyl halides 2, with best results being achieved with alkynyl bromides 2a–2c (Scheme 2). In contrast, 1octyne was not a viable substrate for the nickel-catalyzed C–H alkynylation. Scheme 2. C–H Alkynylation with Alkynes 2 Me
Me
H N
2-pym
R +
H
LiOt-Bu, 1,4-dioxane 90-100 °C, 16 h
Hal
1
H N
3 Me
2-pym
TIPS 3aa 30% (Hal = I) 68% (Hal = Br) 53% (Hal = Cl)
2-pym
R
2 Me
H N
[(DME)NiCl2] (2.5 mol %) 4 (5.0 mol %)
H N
Me 2-pym
TBS 3ab: 50% (Hal = Br)
H N
2-pym
TBDMS 3ac: 62% (Hal = Br)
In consideration of the high catalytic activity of the optimized nickel(II) precatalyst, we became attracted to elucidating its mode of action. To this end, intermolecular competition experiments between different anilines 1 did not show a significant difference in relative reaction efficacy (Scheme 3a).13 The addition of typical radical scavengers led to diminished yields of product 3aa (Scheme 3b). Yet the performance in the presence of stoichiometric amounts of TEMPO was found almost unaltered, rendering an SET-type mechanism unlikely to be operative here. In contrast to our recent nickel-catalyzed C–H with anilines 1,10a,c the C–H alkynylation of isotopically labeled substrate [D5]-1c was not accompanied by a D/H exchange reaction (Scheme 3c).13 This finding is in good
ACS Paragon Plus Environment
Page 3 of 5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis Scheme 4. Nickel-Catalyzed C–H Functionalization of Purine Bases 5
agreement with a kinetic isotope effect (KIE) of kH/kD ≈ 2.6 (Scheme 3d), which is indicative of a kinetically relevant C–H metalation step. Scheme 3. Key Mechanistic Findings.13 (a) competition experiment 2a [(DME)NiCl2] (2.5 mol %) MeO 4 (5.0 mol %) 2-pym LiOtBu, 1,4-dioxane H 100 °C, 16 h
H N
H N
F3C/MeO
+
2-pym
TIPS
3ka:3la / 1:1 (by NMR)
1k / 1l
H N
F3C
2-pym
TIPS
3ka: 29%
3la: 29%
(b) radical scavengers Me
Me H N
2-pym
TIPS
+
2-pym
LiOt-Bu, 1,4-dioxane 100 °C, 16 h
Br 1a
H N
[(DME)NiCl2] (2.5 mol %) 4 (5.0 mol %)
TIPS
2a additive (1.0 equiv) --TEMPO BHT galvinoxyl
3aa yield 61% 58% 36% 16%
Interestingly, an intermolecular competition experiment between the pyrimidyl and the purinyl directing groups revealed the latter to be more powerful in the nickel-catalyzed C–H activation process (Scheme 5).
(c) attempted H/D exchange 98% D 2a (1.2 equiv) H [(DME)NiCl2] (2.5 mol %) N 2-pym 4 (5.0 mol %)
D5
LiOt-Bu, 1,4-dioxane 100 °C, T
D D3
[D]5-1c
98% D H N
D 2-pym
+
H N
D3
2-pym
Scheme 5. Directing Group Ability
D TIPS [D]4-3ca
[D]5-1c
3 h: 9% 16 h: 35%
90% 60%
(d) KIE by independent experiments H N
2-pym
2a [(DME)NiCl2] (2.5 mol %) 4 (5.0 mol %)
H N
2-pym
LiOt-Bu, 1,4-dioxane 100 °C
TIPS
1c H N D5
3ca
2-pym
H N
as above D4
2-pym
TIPS [D]5-1c
kH/kD = 2.6
[D]4-3ca
The unique practical utility of our approach was highlighted by performing the first nickel-catalyzed C–H functionalizations with purine nucleobases (Scheme 4). Thus, the C–H alkynylation of the adenines 5 occurred exclusively by chelation assistance on the aniline moiety, while the significantly more acidic imidazole and pyrimidine C–H bonds remained unchanged. Thereby, the alkynylated purines 6aa–6da were formed as the sole products, which should prove instrumental for future applications to DNA and RNA chemistry.
Finally, the unprecedented metal-catalyzed C–H alkynylation of NH-free anilines 1 set the stage for the expedient synthesis of diversely decorated indoles 7 via a copper-catalyzed intramolecular hydroamination14 approach (Scheme 6). Scheme 6. (a) Diversification and (b) Preparation of Indoles 7
ACS Paragon Plus Environment
ACS Catalysis
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
In conclusion, we have reported on the first nickelcatalyzed C–H alkynylation of electron-rich arenes. Thus, anilines were directly functionalized with excellent positional selectivity, ample scope, and high functional group tolerance. Mechanistic studies provided strong evidence for a kinetically relevant C–H metalation by monodentate chelation assistance. The power of the C–H alkynylation strategy was illustrated by a step-economical indole synthesis, and the first nickel-catalyzed C–H functionalization with purine nucleobases.
ASSOCIATED CONTENT Supporting Information 1
Experimental procedures, characterization data, and H and 13 C NMR spectra for new compounds. This material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION Corresponding Author *
[email protected] Notes The authors declare no competing financial interest.
ACKNOWLEDGMENT Support by the European Research Council under the European Community’s Seventh Framework Program (FP7 2007– 2013)/ERC Grant agreement no. 307535, the DFG (SPP 1807), and the CSC (fellowship to Z.R.) is gratefully acknowledged.
REFERENCES
1.
2.
3. 4. 5.
6.
7.
Representative recent reviews on C–H activation: (a) Gensch, T.; Hopkinson, M. N.; Glorius, F.; Wencel-Delord, J., Chem. Soc. Rev. 2016, 45, 2900-2936. (b) Kim, J.-K.; Shin, K.; Chang, S. Top. Organomet. Chem. 2016, 55, 2951. (c) Borie, C.; Ackermann, L.; Nechab, M. Chem. Soc. Rev. 2016, 45, 1368-1386. (d) Girard, S.-A.; Knauber, T.; Li, C.-J. Angew. Chem. Int. Ed. 2014, 53, 74-100. (e) Rouquet, G.; Chatani, N. Angew. Chem. Int. Ed. 2013, 52, 11726-11743. (f) Arockiam, P. B.; Bruneau, C.; Dixneuf, P. H. Chem. Rev. 2012, 112, 5879-5918. (g) Satoh, T.; Miura, M. Chem. Eur. J. 2010, 16, 11212-11222. (h) Giri, R.; Shi, B.-F.; Engle, K.-M.; Maugel, N.; Yu, J.-Q. Chem. Soc. Rev. 2009, 38, 3242-3272. (i) Ackermann, L.; Vicente, R.; Kapdi, A. Angew. Chem. Int. Ed. 2009, 48, 9792-9826. (j) Bergman, R, G. Nature 2007, 446, 391-393, and references cited therein. (a) Segawa, Y.; Maekawa, T.; Itami, K. Angew. Chem. Int. Ed. 2015, 54, 66-81. (b) Mercier, L. G.; Leclerc, M. Acc. Chem. Res. 2013, 46, 1597-1605. Ackermann, L. Org. Process Res. Dev. 2015, 18, 260-269. Yamaguchi, J.; Yamaguchi, A. D.; Itami, K. Angew. Chem. Int. Ed. 2012, 51, 8960-9009. (a) Brand, J. P.; Waser, J. Chem. Soc. Rev. 2012, 41, 41654179. (b) Dudnik, A. S.; Gevorgyan, V. Angew. Chem. Int. Ed. 2010, 49, 2096-2098. For examples of metal-catalyzed C–H alkynylations, see: (a) Shaikh, A. C.; Shinde, D. R.; Patil, N. T. Org. Lett. 2016, 18, 1056-1059. (b) Li, Y.; Xie, F.; Li, X. J. Org. Chem 2016, 81, 715-722. (c) Tang, G.-D.; Pan, C.-L.; Xie,
8.
Page 4 of 5 F., Org. Biomol. Chem. 2016, 14, 2898-2904. (d) Landge, V. G.; Jaiswal, G.; Balaraman, E., Org. Lett. 2016, 4, 812815. (e) Yang, X.-F.; Hu, X.-H.; Feng, C.; Loh, T.-P. Chem. Commun. 2015, 51, 2532-2535. (f) Sauermann, N.; González, M. J.; Ackermann, L. Org. Lett. 2015, 17, 53165319. (g) Zhang, Z.-Z.; Liu, B.; Wang, C.-Y.; Shi, B.-F. Org. Lett. 2015, 17, 4094-4097. (h) Finkbeiner, P.; Kloeckner, U.; Nachtsheim, B. J. Angew. Chem. Int. Ed. 2015, 54, 4949-4952. (i) Wu, Y.; Yang, Y.; Zhou, B.; Li, Y. J. Org. Chem. 2015, 80, 1946-1951. (j) Shang, M.; Wang, H.-L.; Sun, S.-Z.; Dai, H.-X.; Yu, J.-Q. J. Am. Chem. Soc. 2014, 136, 11590-11593. (k) Feng, C.; Feng, D.; Loh, T.-P. Chem. Commun. 2014, 50, 9865-9868. (l) Collins, K. D.; Lied, F.; Glorius, F. Chem. Commun. 2014, 50, 4459-4461. (m) Xie, F.; Qi, Z.; Yu, S.; Li, X. J. Am. Chem. Soc. 2014, 136, 4780-4787. (n) Feng, C.; Loh, T.-P. Angew. Chem. Int. Ed. 2014, 53, 2722-2726. (o) Tolnai, G. N.; Ganss, S.; Brand, J. P.; Waser, J. Org. Lett. 2013, 15, 112-115. (p) He, J.; Wasa, M.; Chan, K. S. L.; Yu, J.-Q. J. Am. Chem. Soc. 2013, 135, 3387-3390. (q) Ano, Y.; Tobisu, M.; Chatani, N. Org. Lett. 2012, 14, 354-357. (r) Kim, S. H.; Park, S. H.; Chang, S. Tetrahedron 2012, 68, 5162-5166. (s) Ano, Y.; Tobisu, M.; Chatani, N. J. Am. Chem. Soc. 2011, 133, 12984-12986. (t) Kim, S. H.; Yoon, J.; Chang, S. Org. Lett. 2011, 13, 1474-1477. (u) Yang, L.; Zhao, L.; Li, C.-J. Chem. Commun. 2010, 46, 4184-4186. (v) Wei, Y.; Zhao, H.; Kan, J.; Su, W.; Hong, M. J. Am. Chem. Soc. 2010, 132, 2522-2523. (w) Matsuyama, N.; Kitahara, M.; Hirano, K.; Satoh, T.; Miura, M. Org. Lett. 2010, 12, 2358-2361. (x) Brand, J. P.; Charpentier, J.; Waser, J. Angew. Chem. Int. Ed. 2009, 48, 9346-9349. (y) Tobisu, M.; Ano, Y.; Chatani, N. Org. Lett. 2009, 11, 32503252. (z) Seregin, I. V.; Ryabova, V.; Gevorgyan, V. J. Am. Chem. Soc. 2007, 129, 7742-7743. See also: (aa) Trofimov, B. A.; Stepanova, Z. V.; Sobenina, L. N.; Mikhaleva, A.; Ushakov, I. A. Tetrahedron Lett. 2004, 45, 6513-6516. Recent reviews on the use of inexpensive first-row transition metal catalysts for C–H bond functionalization: (a) Liu, W.; Ackermann, L. ACS Catal. 2016, 6, 37433752. (b) Moselage, M.; Li, J.; Ackermann, L. ACS Catalysis 2016, 6, 498-525. (c) Gao, K.; Yoshikai, N. Acc. Chem. Soc. 2014, 47, 1208-1219. (d) Nakamura, E.; Hatakeyama, T.; Ito, S.; Ishizuka, K.; Ilies, L.; Nakamura, M. Org. React. 2014, 83, 1-209. (e) Ackermann, L. J. Org. Chem. 2014, 79, 8948-8954. (f) Yamaguchi, J.; Muto, K.; Itami, K. Eur. J. Org. Chem. 2013, 19-30. (g) Nakao, Y. Chem. Rec. 2011, 11, 242-251. (h) Kulkarni, A.; Daugulis, O. Synthesis 2009, 4087-4109. Recent reviews: (a) Castro, L. C. M.; Chatani, N. Chem. Lett. 2015, 44, 410-421. (b) Yamaguchi, J.; Muto, K.; Itami, K. Eur. J. Org. Chem. 2013, 19-30. Recent contributions: (c) Muto, K.; Hatakeyama, T. Yamaguchi, J.; Itami, K. Chem. Sci. 2015, 6, 6792-6798. (d) Wu, X.; Zhao, Y.; Ge, H. J. Am. Chem. Soc. 2015, 137, 4924-4927. (e) Camasso, N.; Sanford, M. S. Science 2015, 347, 12181220. (f) Wu, X.; Zhao, Y.; Ge, H. J. Am. Chem. Soc. 2014, 136, 1789-1792. (g) Liu, Y.-H.; Liu, Y.-J.; Yan, S.-Y.; Shi, B.-F. Chem. Commun. 2015, 51, 11650-11653. (h) Yan, S.Y.; Liu, Y.-J.; Liu, B.; Liu, Y.-H.; Zhang, Z.-Z.; Shi, B.-F. Chem. Commun. 2015, 51, 7341-7344. (i) Aihara, Y.; Tobisu, M.; Fukumoto, Y.; Chatani, N. J. Am. Chem. Soc. 2014, 136, 15509-15512. (j) Aihara, Y.; Chatani, N. J. Am. Chem. Soc. 2014, 136, 898-901. (k) Xu, H.; Muto, K.; Yamaguchi, J.; Zhao, C.; Itami, K.; Musaev, D. G. J. Am. Chem. Soc. 2014, 136, 14834-14844. (l) Meng, L.; Kamada, Y.; Muto, K.; Yamaguchi, J.; Itami, K. Angew. Chem. Int. Ed. 2013, 52, 10048-10051. (m) Aihara, Y.; Chatani, N. J. Am. Chem. Soc. 2013, 135, 5308-5311. (n) Shiota, H.; Ano, Y.; Aihara, Y.; Fukumoto, Y.; Chatani, N. J. Am. Chem. Soc. 2011, 133, 14952-14955. (o) Yao, T.; Hirano, K.; Satoh, T.; Miura, M. Angew. Chem. Int. Ed.
ACS Paragon Plus Environment
Page 5 of 5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
9.
10.
11.
ACS Catalysis 2012, 51, 775-779. (p) Hachiya, H.; Hirano, K.; Satoh, T.; Miura, M. Angew. Chem. Int. Ed. 2010, 49, 2202-2205, and references cited therein. For selected examples, see: (a) Landge, V. G.; Shewale, C. H.; Jaiswal, G.; Sahoo, M. K.; Midya, S. P.; Balaraman, E., Catal. Sci. Technol. 2016, 6, 1946-1951. (b) Zheng, X.-X.; Du, C.; Zhao, X.-M.; Zhu, X.; Suo, J.-F.; Hao, X.-Q.; Niu, J.-L.; Song, M.-P., J. Org. Chem. 2016, 81, 4002-4011. (c) Tobisu, M.; Takahira, T.; Ohtsuki, A.; Chatani, N. Org. Lett. 2015, 17, 680-683. (d) Liu, Y.-H.; Liu, Y.-J.; Yan, S.Y.; Shi, B.-F. Chem. Commun. 2015, 51, 11650-11653. (e) Yi, J.; Yang, L.; Xia, C.; Li, F. J. Org. Chem. 2015, 80, 6213-6221. (f) Liu, Y.-J.; Liu, Y.-H.; Yan, S.-Y.; Shi, B.-F. Chem. Commun. 2015, 51, 6388-6391. (g) Matsuyama, N.; Kitahara, M.; Hirano, K.; Satoh, T.; Miura, M. Org. Lett. 2010, 12, 2358-2361. (h) Matsuyama, N.; Hirano, K.; Satoh, T.; Miura, M. Org. Lett. 2009, 11, 4156-4159. (a) Ruan, Z.; Lackner, S.; Ackermann, L. Angew. Chem. Int. Ed. 2016, 55, 3153-3157. (b) Song, W.; Lackner, S.; Ackermann, L. Angew. Chem. Int. Ed. 2014, 53, 24772480. (c) Song, W.; Ackermann, L. Chem. Commun. 2013, 49, 6638-6640. (d) Ackermann, L.; Punji, B.; Song, W. Adv. Synth. Catal. 2011, 353, 3325-3329. Selected reviews on the preparation and functionalization of indoles: (a) Bandini, M. Org. Biomol. Chem. 2013, 11, 5206-5212. (b) Inman, M.; Moody, C. J. Chem. Sci. 2013, 4, 29-41. (c) Cacchi, S.; Fabrizi, G.; Goggiamani, A. Org. React. 2012, 76, 281-534. (d) Vicente, R. Org. Biomol. Chem. 2011, 9, 6469-6480. (e) Krüger, K.; Tillack, A.;
12.
13. 14.
Beller, M. Adv. Synth. Catal. 2008, 350, 2153-2167. (f) Ackermann, L. Synlett 2007, 507-526. (g) Humphrey, G. R.; Kuethe, J. T. Chem. Rev. 2006, 106, 2875-2911. A recent review: Gayakhe, V.; Sanghvi, Y. S.; Fairlamb, I. J. S.; Kapdi, A. R. Chem. Commun. 2015, 51, 1194411960. For detailed information, see the Supporting Information. For reviews, see: (a) Pirnot, M. T.; Wang, Y.-M.; Buchwald, S. L. Angew. Chem. Int. Ed. 2016, 55, 48-57. (b) Mueller, T. E.; Hultzsch, K. C.; Yus, M.; Foubelo, F.; Tada, M. Chem. Rev. 2008, 108, 3795-3892. (c) Müller, T. E.; Beller, M. Chem. Rev. 1998, 98, 675-703.
ACS Paragon Plus Environment
