Enantioselective Synthesis of Chiral-at-Cage o-Carboranes via Pd

4 mins ago - Carborane cage chirality is an outstanding issue of great interest as the icosahedral carboranes have wide applications in medicinal and ...
1 downloads 7 Views 2MB Size
Subscriber access provided by TUFTS UNIV

Enantioselective Synthesis of Chiral-at-Cage oCarboranes via Pd-Catalyzed Asymmetric B-H Substitution Ruofei Cheng, Bowen Li, Jie Wu, Jie Zhang, Zaozao Qiu, Wenjun Tang, Shu-Li You, Yong Tang, and Zuowei Xie J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 26 Mar 2018 Downloaded from http://pubs.acs.org on March 26, 2018

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 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 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.

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

Journal of the American Chemical Society

Enantioselective Synthesis of Chiral-at-Cage o -Carboranes via Pd-Catalyzed Asymmetric B−H Substitution Ruofei Cheng,† Bowen Li,‡ Jie Wu,† Jie Zhang,§ Zaozao Qiu,*,†,ǁ Wenjun Tang,‡ Shu-Li You,⊥ Yong Tang,⊥ and Zuowei Xie*,†,§ †

Shanghai-Hong Kong Joint Laboratory in Chemical Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Rd, Shanghai 200032, China ‡ State Key Laboratory of Bio-Organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Rd, Shanghai 200032, China § Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China ǁ Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Rd, Shanghai 200032, China ⊥

State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Rd, Shanghai 200032, China Supporting Information Placeholder

ABSTRACT: Carborane cage chirality is an outstanding issue of great interest as the icosahedral carboranes have wide applications in medicinal and materials chemistry. The synthesis of optically active carborane derivatives, whose chirality is associated with the substitution patterns on the polyhedron, will open new avenues to carborane chemistry. We report herein an efficient method to achieve chiral-at-cage arylation of o-carboranes with high regioand enantio-selectivities by a strategy of palladium-catalyzed asymmetric intramolecular B−H arylation and cyclization. This represents the first example of the enantioselective reaction on carboranes, providing an efficient way for the construction of chiral-at-cage compounds with new skeletons.

als science and medicinal chemistry, where chirality plays an important role in molecular design. It has been documented that addition of substituents to ocarborane cage can lower the symmetry of the resultant molecules.9 For example, the presence of a substituent at the position 4/5 of 1-substituted o-carborane results in the chirality of the molecule (Chart 1, The observer looks onto the pentagonal plane of C(2)-B(3)-B(4)-B(5)-B(6) in o-carborane and then examines the positions of substituents according to the Cahn-Ingold-Prelog rule for the determination of the cage chirality (R or S)10).11 Inspired by the recent reports on fullerene cage chirality12 and ferrocene planar chirality,13 we have established a research program to develop enantioselective methods for the synthesis of optically pure chiral-at-cage o-carborane derivatives, which should add a new page in carborane chemistry.

The importance of chiral compounds and their enantioselective synthesis has been fully acknowledged to date by scientists in both pharmaceutical industry and academia. The stereoselective creation can be achieved by chiral pool, chiral auxiliary, chiral reagents and enantioselective catalysis of transition-metal complexes, as well as organo- and bio-catalysts. Among these asymmetric syntheses, transition-metal-catalyzed enantioselective reaction is one of the most important methods to obtain enantiomerically enriched compounds.1 In the past decades, many excellent asymmetric reactions have been developed for the synthesis of optically pure organic compounds.2 However, none of these reactions has been extended to the preparation of chiral-at-cage carboranes or boron clusters.

Chart 1. The Inherent Cage B(4/5) Chirality of oCarboranes

Icosahedral carboranes are carbon-boron molecular clusters, often viewed as three-dimensional analogues to benzene, which are finding many applications in medicine as boron neutron capture therapy agents or pharmacophores,3 in coordination/organometallic chemistry as versatile ligands,4 in supramolecular design/nanomaterials as functional building blocks,5 in optoelectronics as unique electron sinks and more.6 Although the inherent chirality of carborane cage has been reported, they are only restricted to chiral resolution7 or those tethered with asymmetric substituents.8 The inherent cage chirality is an important yet unresolved issue in the fields of asymmetric synthesis, materi-

We have recently reported a Pd-catalyzed intramolecular B(4)H arylation of o-carboranes in the presence of phosphine ligands.14 We speculated that the use of chiral phosphine ligands may lead to the development of asymmetric version of such arylation reaction. Herein, we report the first example of enantioselective synthesis of chiral-at-cage o-carborane derivatives via Pdcatalyzed asymmetric catalysis. Theoretically, palladium-catalyzed intramolecular arylation of 1-C(O)(o-C6H4Br)-1,2-C2B10H11 (1a) can afford four isomers (Scheme 1). In our previous work, the B(4)/(5)-arylated products (R)-2a and (S)-2a were obtained as racemate via direct cage B−H

ACS Paragon Plus Environment

Journal of the American Chemical Society 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

arylation.14 They are chiral by virtue of the substitution patterns on the icosahedral cluster. When PPh3 was used as a ligand, both enantiomers of (R)-2a and (S)-2a were formed in 1:1 ratio, which were able to be separated by HPLC on the Chiralpak IA-3 column (see Fig. S1-S3 in the SI). Their circular dichroism (CD) spectra exhibited unambiguously mirror images to each other, indicating a pair of enantiomers (Fig. 1). In addition, the absolute configuration of (R)-2a and (S)-2a was determined via single-crystal X-ray analyses of their corresponding B(12) iodinated derivatives (R)-4a and (S)-4a, respectively (Fig. 1). The optical rotation [α]D28 is 176.2 (c = 1.00, CH2Cl2) for (R)-2a and +186.8 (c = 1.00, CH2Cl2) for (S)-2a.

Page 2 of 5

Table 1. Optimization of Pd Sources and Chiral Ligandsa

Scheme 1. Palladium-Catalyzed Intramolecular B−H Arylation of o-Carborane

Entry

[Pd]

L

1

[Pd(allyl)Cl]2

2 3 4 5

Yieldb (%)

ee of

2a

3a

(S)-2a (%)

L1

-

-

-

Pd(OTf)2

L1

97

3

87

Pd(CN)4(BF4)2

L1

97

3

82

Pd(OAc)2

L1

98

2

90

Pd(OAc)2

L2

78

3

-75

6

Pd(OAc)2

L3

84

3

-53

7

Pd(OAc)2

L4

94

5

39

8

Pd(OAc)2

L5

23

2

13

9

Pd(OAc)2

L6

32

3

-33

10

Pd(OAc)2

L7

18

1

-34

11

Pd(OAc)2

L8

68

4

83

Fig. 1. CD Spectra of (R)-2a (blue)/(S)-2a (red) in MeCN (c = 1.33 mM) and Molecular Structures of (R)-4a and (S)-4a

a

Having aforementioned data on (R)-2a and (S)-2a, we then investigated Pd-catalyzed enantioselective intramolecular B−H arylation of o-carborane using chiral phosphine ligand (R)-BIDIME (L1).15 The screening results with L1 ligand were summarized in Table S1 in the SI. A complete consumption of 1a in the presence of 10 mol% of Pd(OAc)2, 10 mol% of L1 and 2 equiv of Cs2CO3 was observed in toluene, giving 90% ee of 2a at 0 oC for 14 h, followed by room temperature (25 oC) for 26 h. The absolute structure of the product 2a from this reaction was assigned as S-configuration by comparing the HPLC and optical rotation of the standard samples (R)- and (S)-2a shown in Scheme 1. We further screened the Pd sources and phosphine chiral ligands using 1a as a model substrate. Compared with Pd(OAc)2, Pd(OTf)2 and Pd(CN)4(BF4)2 gave slightly lower ee of (S)-2a, while [Pd(allyl)Cl]2 was inactive (Table 1, entries 1-4). Different chiral ligands were also examined. As shown in Table 1, L1 proved to be the most efficient chiral ligand in terms of enantioselectivity and reactivity, giving (S)-2a in 98% GC yield with 90% ee (Table 1, entry 4). L2 with methyl group at the 2-position of the oxophosphole ring and 9’-anthracenyl substituted L3 provided diminished reactivities and opposite enantioselectivities (Table 1, entries 5 and 6). L4 offered high activity but moderate ee (Table 1, entry 7). Bisphosphine ligands L5 and L6 were much less active (Table 1, entries 8 and 9). L7 afforded a very low activity (Table 1, entry 10). L8 gave (S)-2a in 68% GC yield and 83% ee (Table1, entry 11). Under the optimized reaction conditions (Table 1, entry 4), the

substrate scope was then examined and the results were summarized in Table 2. The reaction worked well for 9,12-dimethyl substituted o-carborane, affording (S)-2b in 65% yield and 96% ee. Various substituted arylbromides bearing either electron-donating or electron-withdrawing group were well-tolerated to afford the corresponding chiral cyclization products in good to excellent yields (63−90%) with moderate to excellent enantioselectivity (67−92% ee) (2c−2m), in which 4-methyl and 3-fluoro substituted arylbromides 1g and 1j gave high ee values of 92% and 90%, respectively. The aryl chloride was also tolerated in (S)-2m, which provided opportunities for further functionalization. The reaction with naphthylbromide 1n proceeded smoothly to afford the desired product (S)-2n in 93% yield and 83% ee. Notably, the conversion of different thienylbromide substrates was equally well (86-91% yields), albeit with different enantioselectivity. 2Acylthienyl-3-bromide (1p) gave the B−H arylated o-carborane (S)-2p in 71% ee, whereas 1-acylthienyl-2-bromide (1o) and 2acylthienyl-1-bromide (1q) resulted in very low ee’s of 9% and 26%, respectively, which may be related to the chelation of sulfur atom to Pd center.

Reactions were conducted at 0.02 mmol scale in 0.5 mL of toluene at 0 oC for 14 h, then rt for 26 h. bGC yields.

A catalytic cycle for the enantioselective formation of (S)-2a, involving oxidative addition of the C(sp2)−Br bond onto palladium(0), intramolecular B−H palladation and reductive elimination was proposed in Schemes S2-S3 (see the SI). In the crucial B−H bond activation step, the Pd with a chiral ligand can discriminate one among four ortho-B−H bonds. The regioselectivity between B(4/5)- and B(3/6)-positions on o-carborane cage may result from

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

Journal of the American Chemical Society Table 2. Reaction Scopea,b,c

nyl group in TS-R, leading to a bigger Pd-P-C(tBu) angle of 123.9o than that of 116.1o in TS-S. The calculated energy of TS-R is 2.0 kcal/mol higher than that of TS-S, which is in accord with the enantioselectivity observed experimentally. In summary, the first enantioselective synthesis of chiral-atcage o-carboranes has been developed via Pd-catalyzed asymmetric intramolecular B–H arylation under mild reaction conditions. The absolute configuration of the products has been unambiguously assigned. Generally good to excellent yields with up to 96% ee can be achieved. The use of chiral monophosphine ligand is essential for such enantioselective B–H arylation. This work opens avenues to a new class of chiral-at-cage o-carboranes, and also sets a very good example for the development of enantioselective B–H functionalization in other carborane/borane clusters.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Experimental procedures, characterization of the products (PDF), and crystal structures (CIF)

AUTHOR INFORMATION Corresponding Author [email protected] [email protected]

Notes The authors declare no competing financial interests. a

Reaction conditions: 1a (0.2 mmol), Pd(OAc)2 (10 mol%), L1 (10 mol%) and Cs2CO3 (0.4 mmol) in toluene (2 mL) in a closed flask at 0 oC for 14 h, then rt for 26 h. bIsolated yield. cDetermined by chiral HPLC analysis and optical rotation data.

ACKNOWLEDGMENT This work was supported by grants from National Natural Science Foundation of China (no. 21772223 to Z.Q.), CAS-Croucher Funding Scheme, and NSFC/RGC Joint Research Scheme (N_CUHK442/14 to Z.X. and 21461162002 to Y.T.). We thank X.-L. Wan in Shanghai Institute of Organic Chemistry for his assistance with HPLC analysis.

REFERENCES

Fig 2. DFT calculated transition states TS-S and TS-R. The bond distances are given in Å and the bond angles are given in deg. both electronic and steric effects.16 For B(4)- and B(5)enantioselectivity, the P-chiral monophosphine ligand L1 plays a crucial role to achieve the cage chirality. To shed some light on the enantioselectivity in the current asymmetric B−H functionalization reactions, the transition states TS-R and TS-S leading to the final intramolecular arylation products in R and S configuration, respectively, were located by DFT calculations on the basis of concerted metalation-deprotonation (CMD) mechanism, in which the bicarbonate anion acts as the counteranion (Fig 2). In both calculated transition states, the Pd(II) has chiral ligand and one oxygen atom of the bicarbonate anion. The [(B···H)−C−P−O] dihedral angle of 20.3o in TS-R is bigger than that of 13.1o in TSS, suggesting a highly distorted coordination plane of the Pd center in TS-R. This difference arises from a greater steric influence of the t-butyl group of (R)-BI-DIME (L1) over the substrate phe-

(1) (a) Christmann, M.; Bräse, S. Asymmetric Synthesis II; Wiley-VCH: Weinheim, 2012. (b) Lin, G.-Q.; Li, Y.-M.; Chan, A. S. C. Principles and Applications of Asymmetric Synthesis; John Wiley & Sons: New York, 2002. (2) (a) Xie, J.-H.; Zhu, S.-F.; Zhou, Q.-L. Transition Metal-Catalyzed Enantioselective Hydrogenation of Enamines and Imines. Chem. Rev. 2011, 111, 1713-1760. (b) Cherney, A. H.; Kadunce, N. T.; Reisman, S. E. Enantioselective and Enantiospecific Transition-Metal-Catalyzed CrossCoupling Reactions of Organometallic Reagents To Construct C–C Bonds. Chem. Rev. 2015, 115, 9587-9652. (c) Newton, C. G.; Wang, S.-G.; Oliveira, C. C.; Cramer, N. Catalytic Enantioselective Transformations Involving C–H Bond Cleavage by Transition-Metal Complexes. Chem. Rev. 2017, 117, 8908-8976. (3) (a) Issa, F.; Kassiou, M.; Rendina, L. M. Boron in Drug Discovery: Carboranes as Unique Pharmacophores in Biologically Active Compounds. Chem. Rev. 2011, 111, 5701-5722. (b) Scholz, M.; HeyHawkins, E. Carbaboranes as Pharmacophores: Properties, Synthesis, and Application Strategies. Chem. Rev. 2011, 111, 7035-7062. (4) (a) Carboranes 3rd ed.; Grimes, R. N., Eds.; Elsevier: Oxford, UK, 2016. (b) Boron Science: New Technologies and Applications; Hosmane, N. S., Eds.; Taylor & Francis Books/CRC: Boca Raton, FL, 2011. (c) Spokoyny, A. M.; Machan, C. W.; Clingerman, D. J.; Rosen, M. S.; Wiester, M. J.; Kennedy, R. D.; Stern, C. L.; Sarjeant, A. A.; Mirkin, C. A. A Coordination Chemistry Dichotomy for Icosahedral Carborane-based Ligands. Nat. Chem. 2011, 3, 590-596. (d) Yao, Z.-J.; Jin, G.-X. Transition Metal Complexes Based on Carboranyl Ligands Containing N,

ACS Paragon Plus Environment

Journal of the American Chemical Society 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

P, and S Donors: Synthesis, Reactivity and Applications. Coord. Chem. Rev. 2013, 257, 2522-2535. (e) Xie, Z. Advances in the Chemistry of Metallacarboranes of f-Block Elements. Coord. Chem. Rev. 2002, 231, 2346. (5) (a) Koshino, M.; Tanaka, T.; Solin, N.; Suenaga, K.; Isobe, H.; Nakamura, E. Imaging of Single Organic Molecules in Motion. Science 2007, 316, 853-853. (b) Dash, B. P.; Satapathy, R.; Gaillard, E. R.; Maguire, J. A.; Hosmane, N. S. Synthesis and Properties of CarboraneAppended C3-Symmetrical Extended π Systems. J. Am. Chem. Soc. 2010, 132, 6578-6587. (c) Bauduin, P.; Prevost, S.; Farràs, P.; Teixidor, F.; Diat, O.; Zemb, T. A Theta-Shaped Amphiphilic Cobaltabisdicarbollide Anion: Transition From Monolayer Vesicles to Micelles. Angew. Chem. Int. Ed. 2011, 50, 5298-5300. (d) Qian, E. A.; Wixtrom, A. I.; Axtell, J. C.; Saebi, A.; Jung, D.; Rehak, P.; Han, Y.; Moully, E. H.; Mosallaei, D.; Chow, S.; Messina, M. S.; Wang, J. Y.; Royappa, A. T.; Rheingold, A. L.; Maynard, H. D.; Král, P.; Spokoyny, A. M. Atomically Precise Organomimetic Cluster Nanomolecules Assembled via Perfluoroaryl-Thiol SNAr Chemistry. Nat. Chem. 2017, 9, 333. (6) (a) Wee, K.-R.; Cho, Y.-J.; Jeong, S.; Kwon, S.; Lee, J.-D.; Suh, I.H.; Kang, S. O. Carborane-Based Optoelectronically Active Organic Molecules: Wide Band Gap Host Materials for Blue Phosphorescence. J. Am. Chem. Soc. 2012, 134, 17982-17990. (b) Furue, R.; Nishimoto, T.; Park, I. S.; Lee, J.; Yasuda, T. Aggregation-Induced Delayed Fluorescence Based on Donor/Acceptor-Tethered Janus Carborane Triads: Unique Photophysical Properties of Nondoped OLEDs. Angew. Chem. Int. Ed. 2016, 55, 7171-7175. (c) Núñez, R.; Tarrés, M.; Ferrer-Ugalde, A.; de Biani, F. F.; Teixidor, F. Electrochemistry and Photoluminescence of Icosahedral Carboranes, Boranes, Metallacarboranes, and Their Derivatives. Chem. Rev. 2016, 116, 14307-14378. (d) Naito, H.; Nishino, K.; Morisaki, Y.; Tanaka, K.; Chujo, Y. Solid-State Emission of the Anthracene-o-Carborane Dyad from the Twisted-Intramolecular Charge Transfer in the Crystalline State. Angew. Chem. Int. Ed. 2017, 56, 254-259. (e) Tu, D.; Leong, P.; Guo, S.; Yan, H.; Lu, C.; Zhao, Q. Highly Emissive Organic Single-Molecule White Emitters by Engineering o-CarboraneBased Luminophores. Angew. Chem. Int. Ed. 2017, 56, 11370-11374. (f) Guo, J.; Liu, D.; Zhang, J.; Zhang,J.; Miao, Q.; Xie, Z. o-Carborane Functionalized Pentacenes: Synthesis, Molecular Packing and Ambipolar Organic Thin-Film Transistors. Chem. Commun. 2015, 51, 12004-12207. (7) (a) Krasnov, V. P.; Levit, G. L.; Charushin, V. N.; Grishakov, A. N.; Kodess, M. I.; Kalinin, V. N.; Ol'shevskaya, V. A.; Chupakhin, O. N. Enantiomers of 3-Amino-1-methyl-1,2-dicarba-closo-dodecaborane. Tetrahedron: Asymmetry 2002, 13, 1833-1835. (b) Levit, G. L.; Demin, A. M.; Kodess, M. I.; Ezhikova, M. A.; Sadretdinova, L. S.; Ol’shevskaya, V. A.; Kalinin, V. N.; Krasnov, V. P.; Charushin, V. N. Acidic Hydrolysis of N-Acyl-1-Substituted 3-Amino-1,2-dicarba-closo-dodecaboranes. J. Organomet. Chem. 2005, 690, 2783-2786. (c) Levit, G. L.; Krasnov, V. P.; Gruzdev, D. A.; Demin, A. M.; Bazhov, I. V.; Sadretdinova, L. S.; Olshevskaya, V. A.; Kalinin, V. N.; Cheong, C. S.; Chupakhin, O. N.; Charushin, V. N. Synthesis of N-[(3-Amino-1,2-dicarba-closododecaboran-1-yl)acetyl] Derivatives of α-Amino Acids. Collect. Czech. Chem. Commun. 2007, 72, 1697-1706. (d) Krasnov, V. P.; Demin, A. M.; Levit, G. L.; Grishakov, A. N.; Sadretdinova, L. S.; Ol’shevskaya, V. A.; Glukhov, I. V.; Kalinin, V. N.; Charushin, V. N. Determination of Enantiomeric Purity of 1-Substituted 3-Amino-1,2-dicarba-closododecaboranes by HPLC on Chiral Stationary Phases. Russ. Chem. Bull. 2008, 57, 2535-2539. (8) (a) Endo, Y.; Sawabe, T.; Taoda, Y. Electronic Effects of Icosahedral Carboranes. Retentive Solvolysis of (1,2-Dicarba-closododecaboran-1-yl)benzyl p-Toluenesulfonates. J. Am. Chem. Soc. 2000, 122, 180-181. (b) Lee, J.-D.; Co, T. T.; Kim, T.-J.; Kang, S. O. New Types of o-Carborane-Based Chiral Phosphinooxazoline (Cab-PHOX) Ligand Systems: Synthesis and Characterization of Chiral Cab-PHOX Ligands and Their Application to Asymmetric Hydrogenation. Synlett 2009, 2009, 771-774. (c) Stadlbauer, S.; Frank, R.; Maulana, I.; Lönnecke, P.; Kirchner, B.; Hey-Hawkins, E. Synthesis and Reactivity of orthoCarbaborane-Containing Chiral Aminohalophosphines. Inorg. Chem. 2009, 48, 6072-6082. (d) El-Zaria, M. E.; Arii, H.; Nakamura, H. m-CarboraneBased Chiral NBN Pincer-Metal Complexes: Synthesis, Structure, and Application in Asymmetric Catalysis. Inorg. Chem. 2011, 50, 4149-4161. (e) Ching, H. Y. V.; Clifford, S.; Bhadbhade, M.; Clarke, R. J.; Rendina, L. M. Synthesis and Supramolecular Studies of Chiral Boronated Platinum(II) Complexes: Insights into the Molecular Recognition of Carboranes by β-Cyclodextrin. Chem. Eur. J. 2012, 18, 14413-14425. (f) Di Salvo, F.; Tsang, M. Y.; Teixidor, F.; Viñas, C.; Planas, J. G.; Crassous, J.; Vanthuyne, N.; Aliaga-Alcalde, N.; Ruiz, E.; Coquerel, G.; Clevers, S.;

Page 4 of 5

Dupray, V.; Choquesillo-Lazarte, D.; Light, M. E.; Hursthouse, M. B. A Racemic and Enantiopure Unsymmetric Diiron(III) Complex with a Chiral o-Carborane-Based Pyridylalcohol Ligand: Combined Chiroptical, Magnetic, and Nonlinear Optical Properties. Chem. Eur. J. 2014, 20, 1081-1090. (g) Tsang, M. Y.; Di Salvo, F.; Teixidor, F.; Viñas, C.; Planas, J. G.; Choquesillo-Lazarte, D.; Vanthuyne, N. Is Molecular Chirality Connected to Supramolecular Chirality? The Particular Case of Chiral 2Pyridyl Alcohols. Cryst. Growth Des. 2015, 15, 935-945. (9) (a) King, R. B. Chemical Applications of Topology and Group Theory. XXII: Lowest Degree Chirality Polynomials for Regular Polyhedra. J. Math. Chem. 1987, 1, 45-59. (b) Usatov, A. V.; Martynova, E. V.; Dolgushin, F. M.; Peregudov, A. S.; Antipin, M. Y.; Novikov, Y. N. Fullerene and Carborane in One Coordination Sphere: Synthesis and Structure of a Mixed η2-C60 and σ-Carboranyl Complex of Iridium. Eur. J. Inorg. Chem. 2002, 2002, 2565-2567. (c) Gona, K. B.; Gomez-Vallejo, V.; Padro, D.; Llop, J. [18F]Fluorination of o-Carborane via Nucleophilic Substitution: Towards a Versatile Platform for the Preparation of 18FLabelled BNCT Drug Candidates. Chem. Commun. 2013, 49, 1149111493. (d) Dziedzic, R. M.; Martin, J. L.; Axtell, J. C.; Saleh, L. M. A.; Ong, T.-C.; Yang, Y.-F.; Messina, M. S.; Rheingold, A. L.; Houk, K. N.; Spokoyny, A. M. Cage-Walking: Vertex Differentiation by PalladiumCatalyzed Isomerization of B(9)-Bromo-meta-Carborane. J. Am. Chem. Soc. 2017, 139, 7729-7732. (10) For convenience in the designation of the configuration of chiral carboranes and their derivatives, we have used the approach suggested for chiral 7,8-dicarba-nido-undecaborane derivatives. Brunner, H.; Apfelbacher, A.; Zabel, M. Palladium and Rhodium Complexes with Planar-Chiral Carborane Ligands. Eur. J. Inorg. Chem. 2001, 2001, 917924. (11) Plešek, J. G., V.;Heřmánek, S. Chemistry of Boranes. XX. Optical Isomerism in the o-Carborane Series. Collect. Czech. Chem. Commun. 1970, 35, 346-349. (12) (a) Thilgen, C.; Diederich, F. Structural Aspects of Fullerene Chemistry A Journey through Fullerene Chirality. Chem. Rev. 2006, 106, 5049-5135. (b) Nambo, M.; Wakamiya, A.; Itami, K. Palladium-Catalyzed Ttetraallylation of C60 with Allyl Chloride and Allylstannane: Mechanism, Regioselectivity, and Enantioselectivity. Chem. Sci. 2012, 3, 3474-3481. (c) Maroto, E. E.; Izquierdo, M.; Reboredo, S.; Marco-Martínez, J.; Filippone, S.; Martín, N. Chiral Fullerenes from Asymmetric Catalysis. Acc. Chem. Res. 2014, 47, 2660-2670. (d) Rickhaus, M.; Mayor, M.; Juricek, M. Chirality in Curved Polyaromatic Systems. Chem. Soc. Rev. 2017, 46, 1643-1660. (13) (a) Deng, R.; Huang, Y.; Ma, X.; Li, G.; Zhu, R.; Wang, B.; Kang, Y.-B.; Gu, Z. Palladium-Catalyzed Intramolecular Asymmetric C–H Functionalization/Cyclization Reaction of Metallocenes: An Efficient Approach toward the Synthesis of Planar Chiral Metallocene Compounds. J. Am. Chem. Soc. 2014, 136, 4472-4475. (b) Gao, D.-W.; Yin, Q.; Gu, Q.; You, S.-L. Enantioselective Synthesis of Planar Chiral Ferrocenes via Pd(0)-Catalyzed Intramolecular Direct C–H Bond Arylation. J. Am. Chem. Soc. 2014, 136, 4841-4844. (c) Gao, D.-W.; Gu, Q.; Zheng, C.; You, S.-L. Synthesis of Planar Chiral Ferrocenes via Transition-Metal-Catalyzed Direct C–H Bond Functionalization. Acc. Chem. Res. 2017, 50, 351-365. (14) Quan, Y.; Xie, Z. Palladium-Catalyzed Regioselective Intramolecular Coupling of o-Carborane with Aromatics via Direct Cage B–H Activation. J. Am. Chem. Soc. 2015, 137, 3502-3505. (15) Xu, G.; Fu, W.; Liu, G.; Senanayake, C. H.; Tang, W. Efficient Syntheses of Korupensamines A, B and Michellamine B by Asymmetric Suzuki-Miyaura Coupling Reactions. J. Am. Chem. Soc. 2014, 136, 570573. (16) (a) Quan, Y.; Xie, Z. Iridium Catalyzed Regioselective Cage Boron Alkenylation of o-Carboranes via Direct Cage B–H Activation. J. Am. Chem. Soc. 2014, 136, 15513-15516. (b) Lyu, H.; Quan, Y.; Xie, Z. Transition Metal Catalyzed Direct Amination of the Cage B(4)–H Bond in o-Carboranes: Synthesis of Tertiary, Secondary, and Primary oCarboranyl Amines. J. Am. Chem. Soc. 2016, 138, 12727-12730. (c) Quan, Y.; Xie, Z. Palladium-Catalyzed Regioselective Diarylation of oCarboranes by Direct Cage B−H Activation. Angew. Chem. Int. Ed. 2016, 55, 1295-1298. (d) Zhang, X.; Zheng, H.; Li, J.; Xu, F.; Zhao, J.; Yan, H. Selective Catalytic B–H Arylation of o-Carboranyl Aldehydes by a Transient Directing Strategy. J. Am. Chem. Soc. 2017, 139, 14511-14517. (e) Quan, Y.; Qiu, Z.; Xie, Z. Transition-Metal-Catalyzed Selective Cage B−H Functionalization of o-Carboranes. Chem. Eur. J. 2018, DOI: 10.1002/chem.201704937.

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

Journal of the American Chemical Society TOC

ACS Paragon Plus Environment

5