Ni-Catalyzed Regio- and Enantioselective Domino Reductive

Jul 17, 2019 - Transition-metal-catalytic domino reactions represent important advances in synthetic organic chemistry. Their development benefits syn...
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Research Article Cite This: ACS Catal. 2019, 9, 7335−7342

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Ni-Catalyzed Regio- and Enantioselective Domino Reductive Cyclization: One-Pot Synthesis of 2,3-Fused Cyclopentannulated Indolines Yuanyuan Ping,† Kuai Wang,† Qi Pan, Zhengtian Ding, Zhijun Zhou, Ya Guo, and Wangqing Kong* The Center for Precision Synthesis (CPS), Institute for Advanced Studies (IAS), Wuhan University, Wuhan 430072, People’s Republic of China Downloaded via BUFFALO STATE on July 17, 2019 at 17:38:33 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: Transition-metal-catalytic domino reactions represent important advances in synthetic organic chemistry. Their development benefits synthesis by providing highly efficient and step-economical methods to complex molecules with impressive selectivity. Herein, a Ni-catalyzed domino reductive cyclization of acrylamides with alkynyl bromides is reported, enabling rapid assembly of a range of substituted 2,3-fused cyclopentannulated indolines. Preliminary mechanistic studies revealed that tricyclic indolines are afforded through a highly regioselective migratory insertion of 1,3-diynes, which are formed from the homocoupling of alkynyl bromides, into the in situ generated σ-alkyl-Ni(II) species, followed by nucleophilic addition of the resulting alkenyl nickel to unactivated amides. Most importantly, a highly regio- and enantioselective reductive cyclization of acrylamides and internal alkynes has also been developed. This transformation takes place under mild conditions with high efficiency, providing a rapid access to structurally diverse cyclopentannulated indolines in synthetically useful yields with high regioselectivity (>20/1) and enantioselectivity (27 examples, 82−96% ee). KEYWORDS: Ni catalysis, reductive cross-coupling, cyclization, enantioselectivity, 2,3-fused cyclopentannulated indoline, regioselectivity

T

significance, many studies have been directed toward the synthesis of these privileged structures. However, protocols for their enantioselective preparation are still very limited;2 the main strategy allowing access to such tricyclic skeletons has so far relied on [3 + 2] cycloaddition reactions of functionalized indoles with 1,3-dipoles.3 Given the wide structural diversity of chiral cyclopentannulated indolines in target molecules, the development of new strategies to these scaffolds from simple and readily available starting materials continues to be highly valuable. On the other hand, catalytic cross-electrophile coupling reactions have gained extensive attention, as they represent a powerful tool for the construction of diverse C−C bonds and allow reactions to proceed under very mild conditions without any additional prefunctionalization in comparison to classical nucleophilic/electrophilic regimes.4 Despite tremendous advances, this field of expertise remains essentially confined to the formation of a single C−C bond, 5 and highly enantioselective catalytic variants of these processes have rarely been explored.6,7 In connection with our interest in the development of Ni-catalyzed enantioselective cross-electro-

he 2,3-fused cyclopentannulated indolines are widely present as core structures in a large number of synthetic or natural products encompassing a broad range of biological activities such as vindolinine, kopsane, dasyrachine, spermacoceine, and kopsinidine B (Figure 1).1 In view of their broad

Received: May 21, 2019 Revised: June 30, 2019

Figure 1. Representative natural products possessing a cyclopentannulated indoline core. © XXXX American Chemical Society

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DOI: 10.1021/acscatal.9b02081 ACS Catal. 2019, 9, 7335−7342

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ACS Catalysis

Scheme 1. Proposed Strategy for the Synthesis of 2,3-Fused Cyclopentannulated Indolines by a Ni-Catalyzed Tandem Process

alkenylnickel species,11 poorly electrophilic amides have been virtually unexplored.12 Despite the many difficulties, we were still attracted to these challenges, as such a route would offer a unique opportunity to rapidly assemble tricyclic indoline skeletons from simple precursors. Herein, we present the realization of this novel design principle by a Ni-catalyzed tandem process, which enables the one-pot synthesis of highly valuable 2,3-fused cyclopentannulated indoline scaffolds involving multiple C−C bond formations. In addition, to uncover the nature of the reaction intermediates involved in this transformation, control experiments and mechanistic probes were designed. Most importantly, a highly regio- and enantioselective synthesis of 2,3-fused cyclopentannulated indolines through reductive cyclization/coupling of alkyne-tethered aryl bromides with asymmetric internal alkynes has been achieved, and these results will also be presented. We began our investigations by using 1a and 2a as the model substrates to optimize the reaction conditions (Table 1). As expected, our studies revealed that the selectivity for 3aa is challenged by a number of competitive reactions, such as the direct coupling of Ar−Br with alkynyl bromide, the protonation of intermediate A and the arylalkynylation reaction to produce 5aa. After scrupulous evaluation of a range of parameters, we were pleased to find that a combination of NiCl2(DME), 4,4′-dimethoxycarbonyl-2,2′bipyridine (L1), and Mn as reducing agent in THF at 60 °C provided 3aa in 72% isolated yield with excellent chemo- and regioselectivity (entry 1). Using DMA as solvent led to poor

phile coupling of alkenes for the efficient construction of Ncontaining heterocycles,8 we envisaged that 2,3-fused cyclopentannulated indolines 3 might be assembled through the fusion of aryl bromide tethered acrylamides 1 with alkynyl bromides 2 in a cascade fashion (Scheme 1A). A more complete depiction of the presumed catalytic cycle for this tandem reaction is shown in Scheme 1B. Oxidative addition of aryl bromide 1 to Ni(0) species followed by an intramolecular carbonickelation produces the σ-alkyl-NiIIX species A.9 A subsequent regioselective migratory insertion of 1,3-diyne 4, which is formed from the reductive homocoupling of alkynyl bromide 2, into the nickel−alkyl bond of A generates the seven-membered alkenylnickel species B. Intramolecular nucleophilic addition of the nickel−carbon bond of B to the amide leads the nickel alkoxide intermediate C, which can undergo protonolysis to release the desired product 3 and regenerate Ni(0) catalyst upon reduction. At the outset of our investigations, however, it was not clear whether such a protocol could be implemented, as a series of challenges must be addressed. First, the Ni-catalyzed reductive homocoupling of alkynyl bromide 2 to produce 1,3-diyne 4 must be rapid in comparison to the cyclizative coupling of aryl bromide 1 with 2; otherwise, the formation of arylalkynylated product 5 will be unavoidable. Second, controlling the regioselectivity of migratory insertion across alkynes is very difficult, since previous reports of the use of unsymmetrical alkynes that lack electronic or steric biases typically resulted in a mixture of regioisomers.10 Furthermore, although several types of electrophiles have been found to be able to capture 7336

DOI: 10.1021/acscatal.9b02081 ACS Catal. 2019, 9, 7335−7342

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ACS Catalysis Table 1. Optimization of the Reaction Conditionsa

entry

changes from standard conditions

yield of 5aab (%)

yield of 3aab (%)

3aa/3aa′

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

none DMA instead of THF L2 instead of L1 L3 instead of L1 L4 instead of L1 L5 instead of L1 L6 instead of L1 L7 instead of L1 L8 instead of L1 Ni(COD)2 instead of NiCl2(DME) Zn0 instead of Mn0 B2Pin2 instead of Mn0 without NiCl2(DME) without L1 without Mn0

20/1

a Reactions were carried out with 1a (0.1 mmol), 2a (0.3 mmol), Ni catalyst (10 mol %), ligand (20 mol %), Mn0 (0.4 mmol) in 2 mL of THF at 60 °C for 24 h, unless noted otherwise. bIsolated yields.

of the Cα substituents (R2) of the acrylamide double bond on the reaction outcome was tested. Methoxymethyl, benzyl, and phenyl substituents were well compatible (3na−pa). The substrate scope with respect to alkynyl bromides 2 was investigated next (Scheme 3). The alkynyl bromide and iodide are both competent electrophiles and afforded indoline 3aa in good yields. n-Pentyl, phenyl, trifluoromethyl, and fluoro substituents in the para position of the aromatic ring could be efficiently coupled producing compounds 3ab−ae in moderate to good yields. Particularly interesting was the ability to accommodate aryl chloride (3af) or bromide (3ag); the alternative competing diarylated product was not observed.8 These motifs have successfully been used as counterparts in Ni-catalyzed cross-coupling reactions, which provides an additional handle for further derivatization. Substitution in the meta or ortho position was also well tolerated, as demonstrated by the efficient conversion obtained for 3ah− ak. Importantly, heteroaromatic-substituted alkynyl bromides such as 2-thiophene, 3-thiophene, and 3-benzothiophene proved to be amenable substrates, producing 3am−ao in synthetically useful yields, thus showcasing the genuine potential of our protocol. Control experiments were designed to unravel the reaction mechanism (Scheme 4). When 5aa was subjected to our optimized reaction conditions, 3aa was not observed (eq 1); thus, the arylalkynylated product 5 as an intermediate can be ruled out. We have also found that the 1,3-diyne 4aa can be formed in 70% yield by homocoupling of alkynyl bromide 2a under our standard conditions (eq 2). Interestingly, tracking the reaction of 1a with 4aa found that the reaction went to completion after 48 h, delivering 3aa in 71% yield (eq 3).

chemoselectivity for indoline 3aa over arylalkynylated product 5aa (entry 2). As anticipated, the nature of the ligand had a non-negligible effect on the reaction outcome. Most strikingly, the methoxycarbonyl groups of L1 is found to be critical for this transformation, as other bipyridine type ligands L2−L8 resulted in no reaction occurring (entries 3−9). Inferior results were obtained with other nickel-catalyst precursor or reducing agent combinations (entries 10−12). In line with our expectations, formation of product 3aa was not observed in control experiments in which Ni, ligand, or Mn were omitted (entries 13−15). The conditions of entry 1 in Table 1 were subsequently employed to test the generality of this process. We were pleasure to find that a variety of alkene-tethered aryl bromides 1 could undergo cyclizative cross coupling to furnish the target products 3aa−pa in good yields (Scheme 2). The aryl bromide, iodide, and triflate are competent electrophiles and afforded indoline 3aa in good yields. Subsequently, the substitution pattern on the aromatic ring of the aniline moiety was studied. Substitution in a para position relative to the N atom with both electron-donating as well as electronwithdrawing groups was well tolerated to afford the corresponding indolines 3ba−da in good yields. The metaand ortho-substituted anilides and N-(naphthalen-2-yl)amide all posed no problems (3fa−ia, 3ja). Remarkably, a pyridine backbone was perfectly accommodated to furnish the azaindoline 3ka in 60% yield, which is of particular interest due to its prominence in natural products and drug discovery programs.13 The structure of 3ka was unequivocally established by an X-ray crystal diffraction study.14 The cyclizative crosscoupling reaction of N-benzyl acetanilide 1m proceeded efficiently to provide 3ma in 69% yield. Finally, the influence 7337

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ACS Catalysis Scheme 2. Substrate Scope of Aryl Bromides 1

Scheme 4. Mechanistic Study

Scheme 3. Substrate Scope of Alkynyl Bromides 2

Table 1, entry 1). Attempts to accelerate the reaction by adding a catalytic amount of alkynyl bromide 2a found no effect (eq 4). After careful analysis of the reaction process, we realized that there are subtle differences in reaction conditions. In the reactions of 1 with 2, the homocoupling of 2 produced stoichiometric amounts of MnBr2, but at the beginning of the reaction of 1a with 4aa, MnBr2 was not present in the reaction system. Therefore, we set out to investigate the effect of MnBr2 on the reaction. Strikingly, by addition of 1 equiv of MnBr2 to the catalytic reaction of 1a with 4aa, the reaction completed much more quickly, delivering 3aa in 70% yield within 12 h (eq 5). In addition, we found that the reaction of 1a with 2a in the presence of MnBr2 could also be completed within 12 h (eq 6). Taking together, these results clearly demonstrated that MnBr2 plays a key role in significantly accelerating the reaction by promoting the late cyclization process rather than the early homocoupling of alkynyl bromide (compare eqs 5 and 6 with eq 3). To unravel the intermediates involved in this transformation, we synthesized the σ-alkyl-NiII complex 6 following our previous report from the oxidative addition of 1a and subsequent migratory insertion (Scheme 4, eq 8).15 The stoichiometric experiments with complex 6 are particularly illustrative; we found that the target product 3aa was cleanly produced in 74% yield in the presence of MnBr2 (compare eq 9 with eq 7). Moreover, a reaction run without nickel did not consume starting material (Table 1, entry 13), suggesting that direct insertion of Mn0 into aryl bromide is not likely. Taken together, these results support the ideal of a mechanism in

These results provided direct evidence of the mechanism that 1,3-diyne 4 is the key intermediate for this transformation. It seems to be unreasonable that the reaction time of direct cyclization of 1a with 4aa is significantly longer than the reaction time of 1a with 2a (compare Scheme 4, eq 3, with 7338

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ACS Catalysis Table 2. Optimization of Reaction Conditionsa

entry

ligand

additive (equiv)

yield of 8aa (%)b

ee of 8aa (%)c

1 2 3 4 5 6 7

L1 L22 L22 L22 L22 L22 L22

Et3N (2) DIPEA (2) DBU (2) K3PO4 (2) Et3N (4) Et3N (10)

65 52 47 26 24 55 60

92 93 52 72 91 90

a

Reactions were carried out with 1a (0.1 mmol), 7a (0.3 mmol), NiCl2(DME) (10 mol %), ligand (20 mol %), MnBr2 (0.1 mmol), and Mn0 (0.4 mmol) in 2 mL THF at 60 °C for 12 h; NaBH3CN (0.5 mmol) was added and heated at 60 °C for another 12 h, unless noted otherwise. bIsolated yields. cDetermined by HPLC analysis with a chiral column.

which an σ-alkyl-NiII species serves as the key intermediate in the catalytic cycle. However, in the case where MnBr2 was not added, only a trace of product 3aa was observed (eq 10), thus confirming that MnBr2 was indispensable for the reaction to occur. We further attempted to use operando IR to monitor the reaction between 1a and 4aa. As shown in Figures S1 and S2 in the Supporting Information, we were delighted to see not only that the kinetic profiles clearly revealed the consumption of 1a and the formation of 3aa but also that the infrared absorption peak of the CO bond (1665 cm−1) of 1a remained almost unchanged during the first few hours in the reaction without adding MnBr2. However, in the case of adding MnBr2, the absorption intensity of the CO bond began to decrease immediately. These results indicate that MnBr2 may act as a Lewis acid to promote the nucleophilic cyclization process. In addition, the step of carbonyl disappearance, that is, nucleophilic attack of the alkenylnickel species on amide, may be the rate-determining step of this tandem process.16 On the basis of the above mechanistic study where the 1,3diyne is the key intermediate, we questioned whether we could extend the scope of our protocol to simple alkynes. Therefore, 1a and asymmetric alkyne 7a were selected as benchmark substrates to test our hypothesis. Upon modification of the reaction protocol (entry 1, Table 1), wherein MnBr2 proved to be crucial, the yield of indoline 8aa was boosted to 65% (entry 1, Table 2). Since some 2-hydroxyindolines are less stable for silica gel column chromatography, a reductive step was incorporated into the reaction sequence.17 The structure of 8aa was unequivocally established by X-ray crystallographic

analysis.18 Importantly, not even a trace of regioisomer 8aa′ was found in the crude reaction mixtures. To control the absolute stereochemistry of the 2,3-fused cyclopentannulated indolines, an enantioselective variant of the reaction was explored (Table 2). A range of chiral ligands were examined: BOX ligands L9−L12 and PHOX ligands L13 and L14, which are widely used in enantioselective cross-electrophile reactions,7 did not give any desired product. The chiral Pyrox ligand L22 was proved to be the most effective in terms of enantioselectivity (94% ee), albeit with a low yield (39% yield). To our delight, we subsequently found that base played a key role in the reaction outcome. The addition of Et3N was beneficial for the reactivity to give 8aa in 52% yield with 92% ee (entry 2). A comparable result was obtained by the addition of DIPEA (entry 3). However, the utilization of the strong organic base DBU or inorganic base K3PO4 in place of Et3N deteriorated the results (entries 4 and 5). The best result was achieved when an excess of Et3N (10 equiv) was used, providing 8aa in 60% yield with 90% ee (entry 7). The absolute configuration (3R, 8S for 8aa) was determined unambiguously by X-ray crystallographic analysis, and those of all other 2,3-fused cyclopentannulated indoline products were assigned accordingly.19 With the optimized conditions in hand, we set out to explore the scope of alkene-tethered aryl bromides 1. We were pleased to find that a variety of alkene-tethered aryl bromides could undergo cyclizative cross coupling to furnish the target products 8aa−qa in good yields with excellent enantioselectivities (Scheme 5). Different substitution patterns with electrondonating or electron-withdrawing groups on the aniline part 7339

DOI: 10.1021/acscatal.9b02081 ACS Catal. 2019, 9, 7335−7342

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ACS Catalysis Scheme 5. Substrate Scope of Aryl Bromides 1a

Scheme 6. Substrate Scope of Internal Alkynes 7

a 3-(N-Methylmethacrylamido)naphthalen-2-yl trifluoromethanesulfonate was used.

a

Without Et3N. bWithout NaBH3CN reduction.

then explored the cyclization reaction with a wide range of heterocyclic substituted alkynes, such as benzothiophene (8ai), dibenzofuran (8aj), indole (8ak), and thiophene (8am). These results demonstrate that the potential utility of this methodology for the synthesis of medicinally relevant compounds is feasible. The cyclization reaction could also be applied to diarylalkyne (8an) and dialkylalkyne (8ao) in high enantioselectivity, albeit in slightly lower yields. Interestingly, 1,3-diyne 4aa was also accepted as a substrate, leading to the desired product 3aa with 82% ee. There is no significant difference in ee values in Scheme 6 when different substituted internal alkynes 7 are used, indicating that alkynes are not involved in the enantioselectivity-determining step, thus supporting the assumption that the migration insertion (intramolecular acrylamide cyclization) is the enantioselectivity-determining step of this reaction. In conclusion, we have reported a one-pot synthesis of 2,3fused cyclopentannulated indolines through the fusion of arylbromide-tethered acrylamides with alkynyl bromides by a nickel-catalyzed tandem process. Mechanistic studies indicated that the tricyclic indolines are produced through a highly regioselective migratory insertion of 1,3-diynes, which are formed from the homocoupling of alkynyl bromides, into the in situ generated σ-alkyl-NiII species, followed by nucleophilic addition of the resulting alkenyl nickel to unactivated amides. The byproduct MnBr2 can significantly accelerate the nucleophilic cyclization process that may be the rate-

(8ba−ha) were well-tolerated. In addition to aryl bromides, aryl triflate was also compatible to produce the corresponding product 8ja in 88% yield with 86% ee. Importantly, the reaction was successfully applied to the synthesis of the tetracyclic indoline 8la in 94% ee. The presence of a benzyl substituent on the nitrogen atom of 8ma was compatible with the reaction conditions. As the N-benzyl is easily removed, this constitutes a route to N−H indolines. The acrylamide double bond was also amenable to structural variations, so that 8oa− qa could be also efficiently obtained with excellent enantioselectivity. The substrate scope with respect to internal alkynes 7 was investigated next (Scheme 6). Notably, an exquisite regioselectivity profile was found for a wide variety of unsymmetrical alkynes, even without significant steric bias (8ab−am). In all cases, a single regioisomer was obtained, wher the alkyne carbon bearing a less electron donating group (Ar/Het) is connected to the amide carbonyl group of 1 and the alkyne carbon with a more electron donating substituent (alkyl) is attached to the terminal carbon of alkene moiety. Alkynes bearing various substituent groups on the aromatic ring such as OMe (8ac), Me (8ad), Cl (8ae), F (8af), and CF3 (8ag) were well compatible with the current reaction conditions. Whereas substitution meta to the triple bond was tolerated (8ah), no product was observed when the substituent was ortho to the triple bond. To further demonstrate the robustness and generality of synthetic utility of our method, we 7340

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ACS Catalysis

cycloaddition of 3-nitroindoles with vinylcyclopropanes: An entry to stereodefined 2,3-fused cyclopentannulated indoline derivatives. Org. Lett. 2017, 19, 2266−2269. (f) Sun, M.; Zhu, Z.; Gu, L.; Wan, X.; Mei, G.; Shi, F. Catalytic asymmetric dearomative [3 + 2] cycloaddition of electron deficient indoles with all-carbon 1,3-dipoles. J. Org. Chem. 2018, 83, 2341−2348. (g) Zhang, X.; Liu, W.-B.; Tu, H.-F.; You, S.-L. Ligand-enabled Ir-catalyzed intermolecular diastereoselective and enantioselective allylic alkylation of 3-substituted indoles. Chem. Sci. 2015, 6, 4525−4529. (4) For reviews on Ni-catalyzed reductive cross-coupling reactions, see: (a) Knappke, C. E. I.; Grupe, S.; Gärtner, D.; Corpet, M.; Gosmini, C.; Jacobi von Wangelin, A. Reductive cross-coupling reactions between two electrophiles. Chem. - Eur. J. 2014, 20, 6828− 6842. (b) Moragas, T.; Correa, A.; Martin, R. Metal-catalyzed reductive coupling reactions of organic halides with carbonyl-type compounds. Chem. - Eur. J. 2014, 20, 8242−8258. (c) Everson, D. A.; Weix, D. J. Cross-electrophile coupling: principles of reactivity and selectivity. J. Org. Chem. 2014, 79, 4793−4798. (d) Tasker, S. Z.; Standley, E. A.; Jamison, T. F. Recent advances in homogeneous nickel catalysis. Nature 2014, 509, 299−309. (e) Gu, J.; Wang, X.; Xue, W.; Gong, H. Nickel-catalyzed reductive coupling of alkyl halides with other electrophiles: concept and mechanistic considerations. Org. Chem. Front. 2015, 2, 1411−1421. (f) Weix, D. J. Methods and mechanisms for cross-electrophile coupling of Csp2 halides with alkyl electrophiles. Acc. Chem. Res. 2015, 48, 1767−1775. (g) Wang, X.; Dai, Y.; Gong, H. Nickel-catalyzed reductive couplings. Top Curr. Chem. (Z). 2016, 374, 43. (h) Richmond, E.; Moran, J. Recent advances in nickel catalysis enabled by stoichiometric metallic reducing agents. Synthesis 2018, 50, 499−513. (5) For selected examples of Ni-catalyzed reductive cross couplings involving multibond formation, see: (a) Durandetti, M.; Hardou, L.; Lhermet, R.; Rouen, M.; Maddaluno, J. Synthetic applications of the nickel-catalyzed cyclization of alkynes combined with addition reactions in a domino process. Chem. - Eur. J. 2011, 17, 12773− 12783. (b) Yan, C.; Peng, Y.; Xu, X.; Wang, Y. Nickel-mediated interand intramolecular reductive cross-coupling of unactivated alkyl bromides and aryl iodides at room temperature. Chem. - Eur. J. 2012, 18, 6039−6048. (c) Zhao, C.; Jia, X.; Wang, X.; Gong, H. Nicatalyzed reductive coupling of alkyl acids with unactivated tertiary alkyl and glycosyl halides. J. Am. Chem. Soc. 2014, 136, 17645−17651. (d) Peng, Y.; Xu, X.; Xiao, J.; Wang, Y. Nickel-mediated stereocontrolled synthesis of spiroketals via tandem cyclization-coupling of β-bromo ketals and aryl iodides. Chem. Commun. 2014, 50, 472−474. (e) Wang, X.; Liu, Y.; Martin, R. Ni-catalyzed divergent cyclization/ carboxylation of unactivated primary and secondary alkyl halides with CO2. J. Am. Chem. Soc. 2015, 137, 6476−6479. (f) Peng, Y.; Xiao, J.; Xu, X.; Duan, S.; Ren, L.; Shao, Y.; Wang, Y. Stereospecific synthesis of tetrahydronaphtho[2,3-b]furans enabled by a nickel-promoted tandem reductive cyclization. Org. Lett. 2016, 18, 5170−5173. (g) García-Domínguez, A.; Li, Z.; Nevado, C. Nickel-catalyzed reductive dicarbofunctionalization of alkenes. J. Am. Chem. Soc. 2017, 139, 6835−6838. (h) Shimkin, K. W.; Montgomery, J. Synthesis of tetrasubstituted alkenes by tandem metallacycle formation/crosselectrophile coupling. J. Am. Chem. Soc. 2018, 140, 7074−7078. (i) Kuang, Y.; Wang, Y.; Anthony, D.; Diao, T. Ni-catalyzed twocomponent reductive dicarbofunctionalization of alkenes via radical cyclization. Chem. Commun. 2018, 54, 2558−2561. (j) Jin, Y.; Wang, C. Ni-catalysed reductive arylalkylation of unactivated alkenes. Chem. Sci. 2019, 10, 1780−1785. (6) (a) Tollefson, E. J.; Hanna, L. E.; Jarvo, E. R. Stereospecific nickel-catalyzed cross-coupling reactions of benzylic ethers and esters. Acc. Chem. Res. 2015, 48, 2344−2353. (b) Cherney, A. H.; Kadunce, N. T.; Reisman, S. E. Enantioselective and enantiospecific transitionmetal-catalyzed cross-coupling reactions of organometallic reagents to construct C-C bonds. Chem. Rev. 2015, 115, 9587−9652. (c) Lucas, E. L.; Jarvo, E. R. Stereospecific and stereoconvergent cross-couplings between alkyl electrophiles. Nat. Rev. Chem. 2017, 1, 65. (d) Fu, G. C. Transition-Metal Catalysis of Nucleophilic Substitution Reactions: A Radical Alternative to SN1 and SN2 Processes. ACS Cent. Sci. 2017, 3,

determining step of this transformation. Most importantly, an enantioselective reductive cyclization of aryl bromides with asymmetric internal alkynes has also been realized. This transformation takes place under very mild conditions with high efficiency, providing a rapid access to 2,3-fused cyclopentannulated indoline scaffolds in a completely regioselective and highly enantioselective manner.

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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/acscatal.9b02081. Experimental procedures, spectroscopic data, and NMR spectra of all products (PDF) Crystallographic data (CIF) Crystallographic data (CIF) Crystallographic data (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail for W.K.: [email protected]. ORCID

Wangqing Kong: 0000-0003-3260-0097 Author Contributions †

Y.P. and K.W. contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the “1000-Youth Talents Plan”, the National Natural Science Foundation of China (No. 21702149), and the Fundamental Research Funds for the Central Universities (2042018kf0012) is greatly appreciated. We are thankful to Prof. Aiwen Lei at Wuhan University for the generous provision of laboratory and facilities.

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REFERENCES

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DOI: 10.1021/acscatal.9b02081 ACS Catal. 2019, 9, 7335−7342

Research Article

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Enantioselective nickel-catalyzed anti-carbometallative cyclizations of alkynyl electrophiles enabled by reversible alkenylnickel E/Z isomerization. J. Am. Chem. Soc. 2016, 138, 8068−8071. (b) Zhang, X.; Xie, X.; Liu, Y. Nickel-catalyzed cyclization of alkyne-nitriles with organoboronic acids involving anti-carbometalation of alkynes. Chem. Sci. 2016, 7, 5815−5820. (c) Yap, C.; Lenagh-Snow, G. M. J.; Karad, S. N.; Lewis, W.; Diorazio, L. J.; Lam, H. W. Enantioselective nickel-catalyzed intramolecular allylic alkenylations enabled by reversible alkenylnickel E/Z isomerization. Angew. Chem., Int. Ed. 2017, 56, 8216−8220. (d) Karad, S. N.; Panchal, H.; Clarke, C.; Lewis, W.; Lam, H. W. Enantioselective synthesis of chiral cyclopent-2-enones by nickel catalyzed desymmetrization of malonate esters. Angew. Chem., Int. Ed. 2018, 57, 9122−9125. (e) Ranjith Kumar, G.; Kumar, R.; Rajesh, M.; Sridhar Reddy, M. A nickelcatalyzed anti-carbometallative cyclization of alkyne-azides with organoboronic acids: synthesis of 2,3-diarylquinolines. Chem. Commun. 2018, 54, 759−762. (12) There has been only one report of using highly active N-tosyl alkynamides: Gillbard, S. M.; Chung, C.-H.; Karad, S. N.; Panchal, H.; Lewis, W.; Lam, H. W. Synthesis of multisubstituted pyrroles by nickel-catalyzed arylative cyclizations of N-tosyl alkynamides. Chem. Commun. 2018, 54, 11769−11772. (13) (a) Ping, Y.; Li, Y.; Zhu, J.; Kong, W. Construction of quaternary stereocenters by palladium catalyzed carbopalladationinitiated cascade reactions. Angew. Chem., Int. Ed. 2019, 58, 1562− 1573. (b) Schempp, T. T.; Daniels, B. E.; Staben, S. T.; Stivala, C. E. A general strategy for the construction of functionalized azaindolines via domino palladium-catalyzed Heck cyclization/Suzuki coupling. Org. Lett. 2017, 19, 3616−3619 and references therein . (14) CCDC 1870707 (3ka) contains supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre. (15) Attempts to synthesize the corresponding Ni(II) complex using L1 as a ligand have not been successful, probably because it is too active and unstable. (16) The σ-alkyl-NiII complex 6 could be formed at room temperature, but no target product was detected in the catalytic reaction at room temperature, indicating that the intramolecular carbonickelation of alkene is not the turnover-limiting step. (17) Martínez, A.; Webber, M. J.; Müller, S.; List, B. Versatile access to chiral indolines by catalytic asymmetric Fischer indolization. Angew. Chem., Int. Ed. 2013, 52, 9486−9490. (18) CCDC 1878651 (8aa) contains supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre. (19) CCDC 1912176 ((3R,8S)-8aa) contains supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre.

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DOI: 10.1021/acscatal.9b02081 ACS Catal. 2019, 9, 7335−7342