Triarylborane-Catalyzed Reductive N-Alkylation of Amines: A

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Triarylborane-Catalyzed Reductive N-Alkylation of Amines: A Perspective Yoichi Hoshimoto, and Sensuke Ogoshi ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.9b01356 • Publication Date (Web): 03 May 2019 Downloaded from http://pubs.acs.org on May 4, 2019

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Triarylborane-Catalyzed Reductive N-Alkylation of Amines: A Perspective Yoichi Hoshimoto* and Sensuke Ogoshi*

Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan

Abstract

Recent progress on the triarylborane (BAr3)-catalyzed reductive N-alkylation of amines is briefly summarized in this perspective. The highlighted examples are divided into two main classes, i.e., the B(C6F5)3-catalyzed hydroamination of alkynes and subsequent catalytic hydrogenation, as well as the BAr3-catalyzed reductive N-alkylation of carbonyl compounds such as aldehydes, ketones, and carboxylic acids in the presence

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of hydrosilanes or molecular hydrogen. Key aspects on several catalytic systems are emphasized in order to discuss the reaction mechanisms, substrate scope, and practical applications for the preparation of medicinal compounds, as well as the identification of remaining challenges in this area.

KEYWORDS: Triarylboranes; Amine Alkylation; Frustrated Lewis Pairs; Main-Group Catalysis; Hydrogenation; Hydrosilylation

1. Introduction

The development of efficient approaches to construct structural motifs present in bioactive molecules such as natural products, pharmaceuticals, and agrochemicals represents a continuous effort in synthetic organic chemistry. Most of these important molecules contain at least one nitrogen atom,1 and it should thus not be surprising that more than 160 N-containing molecules are found in the “Top 200 Pharmaceutical Products by Prescriptions in 2016”.2 Moreover, ca.140 of these N-containing molecules include N-alkylamino groups, highlighting the relevance of N-alkylation protocols. A variety of methods for the N-alkylation of amines has been developed so far,3 including


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the nucleophilic substitution of activated electrophiles such as alkyl halides and triflates,3ad

the reductive alkylation (or amination) of carbonyl compounds such as aldehydes,

ketones, and carboxylic acids,3e-h the hydrogen-borrowing processes using alcohols or amines,3c,3i-k or the hydroamination of alkenes and alkynes.3l-o These developments have undoubtedly contributed to the expansion of N-alkylation methods for amines. Nevertheless, the current demand for green and sustainable chemical processes has prompted the development of additional/alternative catalytic, and atom-efficient Nalkylation methods that employ readily available catalysts and low-toxicity reagents.1 As intriguing prospects that fulfil those requirements, triarylboranes (henceforth denoted as BAr3 in this perspective, even though the Ar groups may vary within a single molecule) have recently joined the family of catalysts for the N-alkylation of amines, which contradicts the classical expectation that stable N–B bonds would be formed when BAr3 are reacted with an excess of amines. Needless to say, the concept of frustrated Lewis pairs (FLPs)4 played a key role in the development of early examples of the BAr3catalyzed reductive N-alkylation of amines. Today, catalytic sequence including the hydroamination of alkynes and the hydrogenation of enamine intermediates (Scheme


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1a),5-7 as well as the catalytic reductive alkylation with carbonyls in the presence of hydrosilanes or H2 have been developed (Scheme 1b).8-16 This perspective focuses on the recent progress on such BAr3-catalyzed reductive N-alkylations of amines through the functionalization of the N–H bonds in amines. In this context, it is worth noting that the reduction of imines or amides in the presence of catalytic amounts of BAr3 is beyond the scope of this perspective, even though such reactions also afford N-alkylamines.4b,4h,4j,17

Scheme 1. Representative illustration of the BAr3-catalyzed reductive N-alkylations of amines discussed in this perspective.


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2. Hydroamination of Alkynes and Subsequent Hydrogenation

In 2013, Stephan et al. reported a reductive N-alkylation protocol for amines in the presence of catalytic amounts of B(C6F5)3,5,18 which proceeded via an FLP-mediated reaction sequence comprising the intermolecular hydroamination of terminal alkynes to afford enamines and their subsequent hydrogenation (Scheme 2). The key FLPs for hydroamination and hydrogenation reactions were proposed to be generated from amines and B(C6F5)3. Especially, in the latter reaction, enamine intermediates and alkylated amines (i.e. auto-induced catalysis)19 could both serve as a key Lewis base to generate FLPs for the activation of H2;4l however, so far, detailed mechanistic studies for the FLPcatalyzed hydrogenation of enamines have not been reported. The B(C6F5)3-mediated addition of Lewis bases, such as phosphines, thioethers, and N-heterocycles has also been reported;4a,4f however, interestingly, the case of amines successfully expanded to a catalytic manner. In this context, 1,3-proton transfer from a zwitterionic intermediate has been proposed as the crucial step for the regeneration of B(C6F5)3. In addition, the slow


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addition of alkynes is also essential to suppress the reaction of enamines and alkynes with B(C6F5)3, which leads to catalyst deactivation.

Scheme 2. B(C6F5)3-catalyzed intermolecular hydroamination of terminal alkynes and hydrogenation, as reported in ref. 5.

Subsequently, Stephan et al. expanded the aforementioned intermolecular process to the intramolecular N-alkylation of amines proceeding via the B(C6F5)3-


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catalyzed intramolecular hydroamination of terminal alkynes, followed by hydrogenation, which afforded five-, six-, and seven-membered cyclic amines (Scheme 3a).6 The reversible abstraction of the -hydrogen on 1-methyl-2-phenylisoindoline was observed directly, providing insight into the mechanism of the hydrogenation process (Scheme 3b).

Scheme 3. B(C6F5)3-catalyzed intramolecular hydroamination of terminal alkynes and hydrogenation, as reported in ref. 6.

In 2017, Paradies et al. reported the intramolecular N-alkylation of 1 to furnish isoquinoline derivative 2 through an intramolecular hydroamination of the internal alkyne,


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followed by hydrogenation, both of which were catalyzed by B(C6F5)3 (Scheme 4).7 The authors also explored the catalytic activity of B(2,4,6-F3-C6H2)3 and B(2,6-F2-C6H3)3 in the hydroamination of 1 (Scheme 4),20a-c which did not proceed. These results demonstrate the importance of the higher Lewis acidity of B(C6F5)3 under the applied conditions.

Scheme 4. B(C6F5)3-catalyzed intramolecular hydroamination of internal alkyne 1 and hydrogenation, as reported in ref. 7.

3. Reductive Alkylation with Carbonyl Compounds

3.1 Reductive Alkylation using Hydrosilanes

In 1996, Piers et al. reported the B(C6F5)3-catalyzed hydrosilylation of carbonyl compounds.21a Subsequently, Piers et al.21b,c as well as Oestreich et al.18a,21d clarified that


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this reaction proceeds via an SN2-type transition state, in which hydrosilanes coordinate to B(C6F5)3 in an 1 fashion. These seminal studies have undoubtedly contributed to the development of the following reductive alkylations using hydrosilanes.

In 2015, Shang and Fu et al. disclosed a novel strategy for the N-alkylation of primary and secondary amines, i.e., the B(C6F5)3-catalyzed reductive alkylation of amines with carboxylic acids in the presence of hydrosilanes such as Ph3Si–H and polymethylhydrosilane (PMHS) (Scheme 5).8 Selected carboxylic acids (alkyl–COOH) included formic acid for the N-methylation, acetic acid for the N-ethylation, lactic and acrylic acids for the N-propylation, and 2,2,2-trifluoroacetic acid for the Ntrifluoroethylation. In addition, hydroxyl, allyl, and cyano moieties were also tolerated, despite the fact that these functional groups are usually somewhat challenging under reductive conditions. Their N-alkylation method was successfully applied to the synthesis of the commercialized medicinal molecules Butenafine, Cinacalcet, and Piribedil. The reaction was proposed to proceed via the B(C6F5)3-catalyzed reduction of amide intermediates with hydrosilanes, which was subsequently confirmed experimentally.


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Interestingly, they also explored the reductive alkylation of aniline with hexanal under optimized conditions to afford mono-/bis-alkylated amines, which might be the first example of a B(C6F5)3-catalyzed reductive alkylation of amines with aldehydes in the presence of hydrosilanes, further generalized by Ingleson et al.11 later on (vide infra).

Scheme 5. B(C6F5)3-catalyzed reductive N-alkylation of amines with carboxylic acids in the presence of hydrosilanes, as reported in ref. 8.


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Recently, Xu, Fan, and Xiao et al. extended the aforementioned strategy for the Nalkylation of amines using carboxylic acids to tandem cyclization/hydrosilylation processes, furnishing tetrahydroquinoxaline derivatives (Scheme 6a).9 The use of acetyl ketene and levulinic acid resulted in the construction of larger N-heterocycles. Moreover, the asymmetric N-alkylation of amines catalyzed by a mixture of HB(C6F5)2 and a chiral diene,

originally

developed

by

Du

et al.,4c,10 was also explored to yield

tetrahydroquinoxaline derivatives with moderate enantioselectivity (Scheme 6b).

Scheme 6. B(C6F5)3-catalyzed synthesis of tetrahydroquinoxaline via cyclization/hydrosilylation sequences, as reported in ref. 9.


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Soon after the report by Shang and Fu et al., Ingleson et al. published a comprehensive study on the BAr3-catalyzed reductive alkylation of amines with aldehydes/ketones using PhMe2Si–H, where B(C6F5)3 catalysis worked well for the Nalkylation of aryl amines,11 and BPh3 catalysis for alkyl amines (Scheme 7).12 Furthermore, they confirmed the high catalytic activity of in-situ-generated B(3,5-Cl2-C6H3)3 for both aryl and alkyl amines. An advanced aspect of their protocol was the high tolerance of their system toward the presence of low levels of H2O, which enabled using non-purified boron catalysts and solvents in such a water (or moisture)-tolerant FLP system.4i Plausible mechanisms have been proposed based on detailed mechanistic studies, wherein the nucleophile attacking the BAr3-activated hydrosilane (3) would be either the imine intermediate or H2O (Scheme 8). In contrast, in the case of the B(C6F5)3-catalyzed reaction with aniline, Wei

et al. proposed an alternative transition state (TS) comprising B(C6F5)3, PhMe2SiH, H2O, and N-benzalaniline during the formation of iminium intermediate 4, which was proposed to be involved in the most energetically favorable path based on theoretical calculations (Scheme 8).14 Interestingly, Ingleson et al. also explored the use of H2 as a reductant in


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the presence of B(C6F5)3 and confirmed that the targeted N-alkylated amine was not formed, which was subsequently accomplished independently by Soós et al.15 and Hoshimoto and Ogoshi et al.16 (vide infra).

Scheme 7. B(C6F5)3-catalyzed reductive N-alkylation of amines with aldehydes/ketones in the presence of hydrosilanes, as reported in ref. 11 and 12.


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Scheme 8. Simplified mechanism proposed by Ingleson et al. in ref. 11 and 12 and TS structure for the reaction with N-benzalaniline proposed by Wei et al. in ref. 13.

Recently, Otte et al. have reported a system consisting of three coupled catalytic cycles in which epoxides are converted into N-alkylated amines via a B(C6F5)3-catalyzed Meinwald rearrangement of epoxides to afford aldehydes,22 followed by a reductive


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alkylation of aryl amines with the in-situ-generated aldehydes in the presence of PhMe2SiH (Scheme 9).13

Scheme 9. B(C6F5)3-catalyzed tandem Meinwald rearrangement–reductive alkylation with a hydrosilane, as reported in ref. 13.

3.2 Reductive Alkylation using H2

A benefit of the use of BAr3 catalysts in the reductive N-alkylation of amines with carbonyl compounds is their potentially lower toxicity compared to that of well-explored 4d/5d transition-metal-based catalysts. Furthermore, considering the recent demand for green and sustainable chemical processes,1 the catalytic N-alkylation reactions using


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carbonyl compounds described above still generate undesirable waste such as R3SiOH and (R3Si)2O. Molecular hydrogen is thus more suitable reductant as H2O is generated as the sole product. Nevertheless, such a process employing H2 remains underdeveloped as, on one hand, the catalyst should be sufficiently reactive to cleave the enthalpically strong H‒H bond, yet, on the other hand, it should simultaneously tolerate the in-situgenerated H2O, as well as be innocent toward carbonyl substrates.

Soós et al. have recently developed a catalytic reductive N-alkylation of primary and secondary amines with aldehydes and ketones, which was successfully realized in the presence of H2 by expansion of a water-tolerant FLP strategy (Scheme 10).15 They demonstrated that three triarylboranes (5–7) catalyzed the reaction between benzaldehyde and benzylamine in the presence of H2 and molecular sieves in toluene. In addition, 5 is an effective catalyst for the reductive N-alkylation of a variety of alkyl amines, aniline, and p-anisidine, even in the absence of molecular sieves. Intriguingly, the double methylation of benzylamine was also reported using a 37% aqueous solution of formaldehyde under two-phase water/toluene conditions. Although the detailed


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mechanism of such a reductive alkylation was not discussed, the key hydrogenation of the in-situ-generated imines (or iminium species) would be mediated by an FLP comprising 5 and a nitrogen-based Lewis base.

Scheme 10. BAr3-catalyzed reductive N-alkylation of amines with aldehydes/ketones in the presence of H2, as reported in ref. 15.

Hoshimoto and Ogoshi et al. have also reported a catalytic system using H2 for the

N-alkylation of primary aryl amines that bear a wide range of substituents such as hydroxyl, carboxyl, additional amino, primary amide, and primary sulfonamide groups (Scheme 11),16 thus illustrating the excellent functional-group tolerance of such BAr3


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catalysis as these functional groups rarely participate in hitherto reported reductive alkylation systems. The active borane, 8, has previously been confirmed to be watertolerant in the presence of ca. 20 equivalents of H2O;20d however, molecular sieves were essential in the system described by Hoshimoto and Ogoshi et al. In addition, although less active than 8, CF3-substituted triarylborane 9 also showed catalytic activity. The reaction exhibited a zeroth-order and a first-order dependence on the concentration of the imine intermediate and 8, respectively. In addition, the progress of the reaction was significantly affected by the concentration of H2. Thus, a reaction mechanism was proposed based on a tandem processes comprising the 8-catalyzed formation of imines and their subsequent hydrogenation catalyzed by FLPs consisting of 8 and THF, which would include the ratelimiting heterolytic cleavage of H2..


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Scheme 11. BAr3-catalyzed reductive N-alkylation of multiple functionalized aryl amines with aldehydes in the presence of H2, as reported in ref. 16.

Although it is beyond the scope of this perspective, it should be mentioned that the Sn(IV)-catalyzed reductive alkylation of amines with carbonyls and H2 has also been reported by Ashely et al.23

4. Summary and Outlook


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This perspective briefly summarizes the recent progress on the BAr3-catalyzed reductive N-alkylation of amines using hydrosilanes or H2 as reductants. Although the substrate scope and the functional groups applicable remain limited, the B(C6F5)3catalyzed inter- and intramolecular hydroaminations of terminal alkynes and the subsequent hydrogenation of enamine intermediates demonstrate undeniable benefits for the N-functionalization of amines, as these processes showcase green and sustainable features (e.g. high atom efficiency and the use of less toxic reagents). Recently, intramolecular reactions with internal alkynes have also been developed; however, their extension to intermolecular processes currently remains underdeveloped. The reductive N-alkylation of amines using carbonyl compounds has also been realized, using a combination of carboxylic acids and hydrosilanes, aldehydes/ketones and hydrosilanes, as well as aldehydes/ketones and H2. Especially the latter represents an environmentally benign, waste-minimized, and practical route for the functionalization of multiply substituted amines.


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All these examples should be expected to provide novel opportunities for the preparation of important and useful N-alkylated amines using BAr3 catalysts; conversely, the corresponding asymmetric variants remain very challenging, especially when H2 is employed.4c,10,24 It should thus be extremely interesting to follow how chemists will address this challenge in the near future.

AUTHOR INFORMATION

Corresponding Author *[email protected]. *[email protected]

ACKNOWLEDGMENT

This work was supported by Grants-in Aid for Young Scientists (JSPS KAKENHI Grant Number JP18K14219) and the Grants-in Aid for Scientific Research on Innovative Areas “Precisely Designed Catalysts with Customized Scaffolding” (JSPS KAKENHI Grant Number JP15H05803).


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REFERENCES (1) (a) Bryan, M. C.; Dunn, P. J.; Entwistle, D.; Gallou, F.; Koenig, S. G.; Hayler, J. D.; Hickey, M. R.; Hughes, S.; Kopach, M. E.; Moine, G.; Richardson, P.; Roschangar, F.; Steven, A.; Weiberth, F. J. Key Green Chemistry Research Areas from a Pharmaceutical Manufacturers’ Perspective Revisited. Green Chem. 2018, 20, 5082–5103. (b) Constable, D. J. C.; Dunn, P. J.; Hayler, J. D.; Humphrey, G. R.; Leazer, J. L.; Linderman, R. J.; Lorenz, K.; Manley, J.; Pearlman, B. A.; Wells, A.; Zaks, A.; Zhang, T. Y. Key Green Chemistry Research Areas - A Perspective from Pharmaceutical Manufacturers. Green

Chem. 2007, 9, 411–420. (c) Froidevaux, V.; Negrell, C.; Caillol, S.; Pascault, J. P.; Boutevin, B. Biobased Amines: From Synthesis to Polymers; Present and Future. Chem.

Rev. 2016, 116, 14181–14224.

(2)

(a) Qureshi, M. H.; Smith, D. T.; Delost, M. D.; Njardarson, J. T.

https://njardarson.lab.arizona.edu/sites/njardarson.lab.arizona.edu/files/2016Top200Ph armaceuticalPrescriptionSalesPosterLowResV2.pdf. (b) McGrath, N. A.; Brichacek, M.;


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Njardarson, J. T. A Graphical Journey of Innovative Organic Architectures That Have Improved Our Lives. J. Chem. Educ. 2010, 87, 1348–1349.

(3) For selected books, see: (a) Lawrence, S. A. Amines: Synthesis, Properties and

Applications; Cambridge University Press, 2004. (b) Ricci, A. Modern Amination Methods, Wiley-VCH, Weinheim, 2008. For selected recent reviews, see: (c) Legnani, L.; Bhawal, B. N.; Morandi, B. Recent Developments in the Direct Synthesis of Unprotected Primary Amines. Synthesis 2017, 49, 776–789. (d) Salvatore, R. N.; Yoon, C. H.; Jung, K. W. Synthesis of Secondary Amines. Tetrahedron 2001, 57, 7785–7811. (e) Li, B.; Sortais, J.B.; Darcel, C. Amine Synthesis via Transition Metal Homogeneous Catalyzed Hydrosilylation. RSC Adv. 2016, 6, 57603–57625. (f) Nugent, T. C.; El-Shazly, M. Chiral Amine Synthesis - Recent Developments and Trends for Enamide Reduction, Reductive Amination, and Imine Reduction. Adv. Synth. Catal. 2010, 352, 753–819. (g) CabreroAntonino, J. R.; Adam Ortiz, R.; Beller, M. Catalytic Reductive N-Alkylations Using CO2 and Carboxylic Acid Derivatives: Recent Progress and Developments. Angew. Chem.,

Int. Ed. 10.1002/anie.201810121. (h) Liu, X. F.; Li, X. Y.; Qiao, C.; He, L. N. Transition-


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Page 24 of 34

Metal-Free Catalysis for the Reductive Functionalization of CO2 with Amines. Synlett 2018, 29, 548–555. (i) Yang, Q.; Wang, Q.; Yu, Z. Substitution of Alcohols by NNucleophiles via Transition Metal-Catalyzed Dehydrogenation. Chem. Soc. Rev. 2015,

44, 2305–2329. (j) Shimizu, K. I. Heterogeneous Catalysis for the Direct Synthesis of Chemicals by Borrowing Hydrogen Methodology. Catal. Sci. Technol. 2015, 5, 1412– 1427. (k) Nixon, T. D.; Whittlesey, M. K.; Williams, J. M. J. Transition Metal Catalyzed Reactions of Alcohols Using Borrowing Hydrogen Methodology. Dalton Trans. 2009, 5, 753–762. (l) Bernoud, E.; Lepori, C.; Mellah, M.; Schulz, E.; Hannedouche, J. Recent Advances in Metal Free- and Late Transition Metal-Catalyzed Hydroamination of Unactivated Alkenes. Catal. Sci. Technol. 2015, 5, 2017–2037. (m) Coman, S. M.; Parvulescu, V. I. Nonprecious Metals Catalyzing Hydroamination and C-N Coupling Reactions. Org. Process Res. Dev. 2015, 19, 1327–1355. (n) Huang, L.; Arndt, M.; Gooßen, K.; Heydt, H.; Gooßen, L. J. Late Transition Metal-Catalyzed Hydroamination and Hydroamidation. Chem. Rev. 2015, 115, 2596–2697. (o) Pirnot, M. T.; Wang, Y. M.; Buchwald, S. L. Copper Hydride Catalyzed Hydroamination of Alkenes and Alkynes.

Angew. Chem., Int. Ed. 2016, 55, 48–57.


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(4) For recent reviews, see: (a) Stephan, D. W.; Erker, G. Frustrated Lewis Pairs: MetalFree Hydrogen Activation and More. Angew. Chem., Int. Ed. 2010, 49, 46–76. (b) Paradies, J. Frustrated Lewis Pair Catalyzed Hydrogenations. Synlett 2013, 24, 777–780. (c) Feng, X.; Du, H. Metal-Free Asymmetric Hydrogenation and Hydrosilylation Catalyzed by Frustrated Lewis Pairs. Tetrahedron Lett. 2014, 55, 6959–6964. (d) Revunova, K.; Nikonov, G. I. Main Group Catalyzed Reduction of Unsaturated Bonds. Dalton Trans. 2015, 44, 840–866. (e) Oestreich, M.; Hermeke, J.; Mohr, J. A Unified Survey of Si-H and H-H Bond Activation Catalyzed by Electron-Deficient Boranes. Chem. Soc. Rev. 2015,

44, 2202–2220. (f) Stephan, D. W.; Erker, G. Frustrated Lewis Pair Chemistry: Development and Perspectives. Angew. Chem., Int. Ed. 2015, 54, 6400–6441. (g) Weicker, S. A.; Stephan, D. W. Main Group Lewis Acids in Frustrated Lewis Pair Chemistry: Beyond Electrophilic Boranes. Bull. Chem. Soc. Jpn. 2015, 1003–1016. (h) Scott, D. J.; Fuchter, M. J.; Ashley, A. E. Designing Effective “Frustrated Lewis Pair” Hydrogenation Catalysts. Chem. Soc. Rev. 2017, 46, 5689–5700. (i) Fasano, V.; Ingleson, M. J. Recent Advances in Water-Tolerance in Frustrated Lewis Pair Chemistry.

Synthesis 2018, 50, 1783–1795. (j) Lam, J.; Szkop, K. M.; Mosaferi, E.; Stephan, D. W.


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Page 26 of 34

FLP Catalysis: Main Group Hydrogenations of Organic Unsaturated Substrates. Chem.

Soc. Rev. 2019, 10.1039/C8CS00277K. (k) Jupp, A. R.; Stephan, D. W. New Directions for Frustrated Lewis Pair Chemistry. Trends Chem. 2019, 1, 35–48. (l) Paradies, J. Mechanisms in Frustrated Lewis Pair-Catalyzed Reactions. Eur. J. Org. Chem. 2019, 283–294.

(5) Mahdi, T.; Stephan, D. W. Frustrated Lewis Pair Catalyzed Hydroamination of Terminal Alkynes. Angew. Chem., Int. Ed. 2013, 52, 12418–12421.

(6) Mahdi, T.; Stephan, D. W. Stoichiometric and Catalytic Inter- and Intramolecular Hydroamination of Terminal Alkynes by Frustrated Lewis Pairs. Chem.-Eur. J. 2015, 21, 11134–11142.

(7) Tussing, S.; Ohland, M.; Wicker, G.; Flörke, U.; Paradies, J. Borane-Catalyzed Indole Synthesis through Intramolecular Hydroamination. Dalton Trans. 2017, 46, 1539– 1545.

(8) Fu, M. C.; Shang, R.; Cheng, W. M.; Fu, Y. Boron-Catalyzed N-Alkylation of Amines Using Carboxylic Acids. Angew. Chem., Int. Ed. 2015, 54, 9042–9046.


26

Page 27 of 34 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

(9) Pan, Y.; Chen, C.; Xu, X.; Zhao, H.; Han, J.; Li, H.; Xu, L.; Fan, Q.; Xiao, J. MetalFree Tandem Cyclization/Hydrosilylation to Construct Tetrahydroquinoxalines. Green

Chem. 2018, 20, 403–411.

(10) Meng, W.; Feng, X.; Du, H. Frustrated Lewis Pairs Catalyzed Asymmetric MetalFree Hydrogenations and Hydrosilylations. Acc. Chem. Res. 2018, 51, 191–201.

(11) Fasano, V.; Radcliffe, J. E.; Ingleson, M. J. B(C6F5)3-Catalyzed Reductive Amination Using Hydrosilanes. ACS Catal. 2016, 6, 1793–1798.

(12) Fasano, V.; Ingleson, M. J. Expanding Water/Base Tolerant Frustrated Lewis Pair Chemistry to Alkylamines Enables Broad Scope Reductive Aminations. Chem.-Eur. J. 2017, 23, 2217–2224.

(13) Tiddens, M. R.; Klein Gebbink, R. J. M.; Otte, M. The B(C6F5)3-Catalyzed Tandem Meinwald Rearrangement-Reductive Amination. Org. Lett. 2016, 18, 3714–3717.


27

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Page 28 of 34

(14) Chen, H.; Yan, L.; Wei, H. Mechanism of Boron-Catalyzed N-Alkylation of Primary and Secondary Arylamines with Ketones Using Silanes under “Wet” Conditions.

Organometallics 2018, 37, 3698–3707.

(15) Dorkó, É.; Szabó, M.; Kótai, B.; Pápai, I.; Domján, A.; Soós, T. Expanding the Boundaries of Water-Tolerant Frustrated Lewis Pair Hydrogenation: Enhanced Back Strain in the Lewis Acid Enables the Reductive Amination of Carbonyls. Angew. Chem.,

Int. Ed. 2017, 56, 9512–9516.

(16) Hoshimoto, Y.; Kinoshita, T.; Hazra, S.; Ohashi, M.; Ogoshi, S. Main-GroupCatalyzed Reductive Alkylation of Multiply Substituted Amines with Aldehydes Using H2.

J. Am. Chem. Soc. 2018, 140, 7292–7300.

(17) For selected recent examples, see: (a) Chadwick, R. C.; Kardelis, V.; Lim, P.; Adronov, A. Metal-Free Reduction of Secondary and Tertiary N-Phenyl Amides by Tris(pentafluorophenyl)boron-Catalyzed Hydrosilylation. J. Org. Chem. 2014, 79, 7728−7733. (b) Gandhamsetty, N.; Joung, S.; Park, S. W.; Park, S.; Chang, S. BoronCatalyzed Silylative Reduction of Quinolines: Selective sp3 C-Si Bond Formation. J. Am.


28

Page 29 of 34 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

Chem. Soc. 2014, 136, 16780–16783. (c) Gandhamsetty, N.; Jeong, J.; Park, J.; Park, S.; Chang, S. Boron-Catalyzed Silylative Reduction of Nitriles in Accessing Primary Amines and Imines. J. Org. Chem. 2015, 80, 7281–7287. (d) Huang, P. Q.; Lang, Q. W.; Wang, Y. R. Mild Metal-Free Hydrosilylation of Secondary Amides to Amines. J. Org.

Chem. 2016, 81, 4235−4243. (e) Khan, I.; Manzotti, M.; Tizzard, G. J.; Coles, S. J.; Melen, R. L.; Morrill, L. C. Frustrated Lewis Pair (FLP)-Catalyzed Hydrogenation of Aza-MoritaBaylis-Hillman Adducts and Sequential Organo-FLP Catalysis. ACS Catal. 2017, 7, 7748– 7752. (f) Li, R.; Chen, Y.; Jiang, K.; Wang, F.; Lu, C.; Nie, J.; Chen, Z.; Yang, G.; Chen, Y. C.; Zhao, Y.; Ma, Chao. B(C6F5)3-Catalyzed Redox-Neutral β-Alkylation of Tertiary Amines Using p -Quinone Methides via Borrowing Hydrogen. Chem. Commun. 2019, 55, 1217–1220. (g) Sitte, N. A.; Bursch, M.; Grimme, S.; Paradies, J. Frustrated Lewis Pair Catalyzed Hydrogenation of Amides: Halides as Active Lewis Base in the Metal-Free Hydrogen Activation. J. Am. Chem. Soc. 2019, 141, 159–162. For recent reviews, see: (h) Chardon, A.; Morisset, E.; Rouden, J.; Blanchet, J. Recent Advances in Amide Reductions. Synthesis 2018, 50, 984–997. (i) Hackel, T.; McGrath, N. A.


29

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Page 30 of 34

Tris(Pentafluorophenyl)Borane-Catalyzed Reactions Using Silanes. Molecules 2019, 24, 432.

(18) For selected recent reviews on B(C6F5)3, see: (a) Piers, W. E.; Chivers, T. Pentafluorophenylboranes: From Obscurity to Applications. Chem. Soc. Rev. 1997, 26, 345–354. (b) Erker, G. Tris(pentafluorophenyl)borane: a special boron Lewis acid for special reactions Dalton Trans. 2005, 1883–1890. (c) Melen, R. L. Applications of Pentafluorophenyl Boron Reagents in the Synthesis of Heterocyclic and Aromatic Compounds. Chem. Commun. 2014, 50, 1161–1174. (d) Lawson, J. R.; Melen, R. L. Tris(Pentafluorophenyl)Borane and Beyond: Modern Advances in Borylation Chemistry.

Inorg. Chem. 2017, 56, 8627–8643.

(19) (a) Rokob, T. A.; Hamza, A.; Stirling, A.; Pápai, I. On the Mechanism of B(C6F5)3Catalyzed Direct Hydrogenation of Imines: Inherent and Thermally Induced Frustration.

J. Am. Chem. Soc. 2009, 131, 2029–2036. (b) Privalov, T. The Role of Amine–B(C6F5)3 Adducts in the Catalytic Reduction of Imines with H2: A Computational Study. Eur. J.

Inorg. Chem. 2009, 2229–2237. (c) Tussing, S.; Greb, L.; Tamke, S.; Schirmer, B.; Muhle-


30

Page 31 of 34 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

Goll, C.; Luy, B.; Paradies, J. Autoinduced Catalysis and Inverse Equilibrium Isotope Effect in the Frustrated Lewis Pair Catalyzed Hydrogenation of Imines. Chem. Eur. J. 2015, 21, 8056–8059. (d) Tussing, S.; Kaupmees, K.; Paradies, J. Structure-Reactivity Relationship in the Frustrated Lewis Pair (FLP)-catalyzed Hydrogenation of Imines.

Chem. Eur. J. 2016, 22, 7422–7426.

(20) (a) Chakraborty, D.; Rodriguez, A.; Chen, E. Y.-X. Catalytic Ring-Opening Polymerization of Propylene Oxide by Organoborane and Aluminum Lewis Acids.

Macromolecules 2003, 36, 5470–5481. (b) Naumann, D.; Butler, H.; Gnann, R. Preparation and Properties of New Tris(fluoroary1)boranes. Z. Anorg. Allg. Chem. 1992,

618, 74–76. (c) Greb, L.; Daniliuc, C. G.; Bergander, K.; Paradies, J. Functional-Group Tolerance in Frustrated Lewis Pairs: Hydrogenation of Nitroolefins and Acrylates. Angew.

Chem., Int. Ed. 2013, 52, 5876–5879. (d) Gyömöre, Á.; Bakos, M.; Földes, T.; Pápai, I.; Domján, A.; Soós, T. Moisture-Tolerant Frustrated Lewis Pair Catalyst for Hydrogenation of Aldehydes and Ketones. ACS Catal. 2015, 5, 5366–5372.


31

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Page 32 of 34

(21) (a) Parks, D. J.; Piers, W. E. Tris(pentafluorophenyl)boron-Catalyzed Hydrosilation of Aromatic Aldehydes, Ketones, and Esters. J. Am. Chem. Soc. 1996, 118, 9440–9441. (b) Parks, D. J.; Blackwell, J. M.; Piers, W. E. Studies on the Mechanism of B(C6F5)3Catalyzed Hydrosilation of Carbonyl Functions. J. Org. Chem. 2000, 65, 3090–3098. (c) Houghton, A. Y.; Hurmalainen, J.; Mansikkamäki, A.; Piers, W. E.; Tuononen, H. M. Direct observation of a borane–silane complex involved in frustrated Lewis-pair-mediated hydrosilylations. Nat. Chem. 2014, 6, 983–988. (d) Rendler, S.; Oestreich, M. Conclusive Evidence for an SN2-Si Mechanism in the B(C6F5)3-Catalyzed Hydrosilylation of Carbonyl Compounds: Implications for the Related Hydrogenation. Angew. Chem. Int. Ed. 2008,

47, 5997–6000.

(22) (a) Ishihara, K.; Hanaki, N.; Yamamoto, H. Tris(pentafluorophenyl)boron as an Efficient Catalyst in the Stereoselective Rearrangement of Epoxides. Synlett 1995, 7, 721–722. (b) Suda, K.; Kikkawa, T.; Nakajima, S. I.; Takanami, T. Highly Regio- and Stereoselective Rearrangement of Epoxides to Aldehydes Catalyzed by High-Valent Metalloporphyrin Complex, Cr(TPP)OTf. J. Am. Chem. Soc. 2004, 126, 9554–9555.


32

Page 33 of 34 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

(23) Sapsford, J. S.; Scott, D. J.; Allcock, N. J.; Fuchter, M. J.; Tighe, C. J.; Ashley, A. E. Direct Reductive Amination of Carbonyl Compounds Catalyzed by a Moisture Tolerant Tin(IV) Lewis Acid. Adv. Synth. Catal. 2018, 360, 1066–1071.

(24) (a) Lindqvist, M.; Borre, K.; Axenov, K.; Kótai, B.; Nieger, M.; Leskelä, M.; Pápai, I.; Repo, T. Chiral Molecular Tweezers: Synthesis and Reactivity in Asymmetric Hydrogenation. J. Am. Chem. Soc. 2015, 137, 4038–4041. (b)

Süsse, L.; Hermeke,

J.; Oestreich, M. The Asymmetric Piers Hydrosilylation. J. Am. Chem. Soc. 2016, 138, 6940–6943. (c) Lam, J.; Günther, B. A. R.; Farrell, J. M.; Eisenberger, P.; Bestvater, B. P.; Newman, P. D.; Melen, R. L.; Crudden, C. M.; Stephan, D. W. Chiral Carbene-Borane Adducts: Precursors for Borenium Catalysts for Asymmetric FLP Hydrogenations. Dalton

Trans. 2016, 45, 15303–15316. (d) Ye, K.-Y.; Wang, X.; Daniliuc, C. G.; Kehr, G.; Erker, G. A Ferrocene-Based Phosphane/Borane Frustrated Lewis Pair for Asymmetric Imine Reduction. Eur. J. Inorg. Chem. 2017, 368–371. (e) Tu, X. S.; Zeng, N. N.; Li, R. Y.; Zhao, Y. Q.; Xie, D. Z.; Peng, Q.; Wang, X. C. C2-Symmetric Bicyclic Bisborane Catalysts: Kinetic or Thermodynamic Products of a Reversible Hydroboration of Dienes. Angew.


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Page 34 of 34

Chem., Int. Ed. 2018, 57, 15096–15100. (f) Li, X.; Tian, J.; Liu, N.; Tu, X.; Zeng, N.; Wang, X.

Spiro-Bicyclic

Bisborane

Catalysts

for

Metal-Free

Chemoselective

and

Enantioselective Hydrogenation of Quinolines. Angew. Chem., Int. Ed. 2019, 58, 4664– 4668.

TOC


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