No. 1] Proc. Jpn. Acad., Ser. B 90 (2014) 1

Review Transition metal catalyzed borylation of functional :-systems

† By Hiroshi SHINOKUBO*1,

(Communicated by Akira SUZUKI, M.J.A.)

Abstract: Borylated functional :-systems are useful building blocks to enable efficient synthesis of novel molecular architectures with beautiful structures, intriguing properties and unique functions. Introduction of boronic substituents to a variety of extended :-systems can be achieved through either iridium-catalyzed direct C–H borylation or the two-step procedure via electrophilic halogenation followed by palladium-catalyzed borylation. This review article focuses on our recent progress on borylation of large :-conjugated systems such as porphyrins, perylene bisimides, hexabenzocoronenes and dipyrrins.

Keywords: transition-metal catalyst, C–H activation, boron, porphyrin, polyaromatic hydrocarbons, BODIPY

Recently, direct functionalization through C–H Introduction bond cleavage with transition metal complexes Functional :-systems have gained its impor- has proven to be powerful tools for regioselective tance as organic optelectronic materials as well as the modification of aromatic compounds.2) Among such classical but widespread use in dyes and pigments.1) a type of reactions, iridium-catalyzed direct C–H Prospective application of functional :-systems borylation of aromatic compounds developed by covers a whole range of organic materials for OFET Smith, Hartwig, Ishiyama and Miyaura has emerged (organic field effect transistors), OLED (organic as an efficient route to organoboron compounds.3),4) light-emitting diodes), OPV (organic photovoltaic A dioxaborolanyl group can be efficiently introduced cells), non-linear optics, biosensors, optical memory to aromatic and heteroaromatic compounds under and so forth. To obtain desirable properties such as very mild reaction conditions (Scheme 1). This optical and electronic characters as well as stability, reaction is not only interesting in light of its reaction solubility and morphology of materials, introduction mechanism involving an efficient C–H cleavage of appropriate substituents to the periphery of :- process, but also provides organoboranes which systems is often essential. This kind of modification of are otherwise difficult to prepare by conventional :-systems has been achieved through conventional methods, clearly demonstrating the power of tran- electrophilic aromatic substitution reactions such as sition metal catalysis in organic synthesis. Friedel–Crafts reactions. However, these classical As a further extension of this strategy, Miyaura, methodologies generally require rather harsh reaction Ishiyama and coworkers have reported iridium- conditions, which are sometimes incompatible with catalyzed C–H borylation of benzoate and reactive functional groups. Moreover, regioselectivity aryl with electron-deficient phosphine li- of these electrophilic reactions generally controlled gands (Scheme 2).5) This protocol allows regioselec- by the intrinsic electronic factor of the individual :- tive introduction of a boryl substituent at the ortho conjugated system, resulting in difficulty to attain position to the carbonyl group on aromatic rings. different types of regiocontrol. In addition, aromatic boronic esters can be conveniently prepared through palladium-catalyzed *1 Department of Applied Chemistry, Graduate School of borylation of aryl halides with the diboron reagent Engineering, Nagoya University, Nagoya, Japan. 6) † (Scheme 3). When aryl halides are readily available, Correspondence should be addressed: H. Shinokubo, this protocol is often quite effective to access Department of Applied Chemistry, Graduate School of Engineer- ing, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, functionalized aryl- and heteroarylboronic esters. Japan (e-mail: [email protected]). Importantly, iridium-catalyzed C–H borylation re- doi: 10.2183/pjab.90.1 ©2014 The Japan Academy 2 H. SHINOKUBO [Vol. 90,

[Ir(OMe)cod]2 Borylation dtbpy B2pin2 H + B2pin2 Bpin hexane, rt [Ir(OMe)cod]2 FG FG dtbpy pinB Bpin FG = functional group cyclohexane 80 °C 97% 1 2 [Ir(OMe)cod]2 dtbpy + B pin pinB Bpin 2 2 B pin H hexane, rt Bpin 2 2 X X [Ir(OMe)cod]2 X = O, NH, S dtbpy cyclohexane 80 °C t-Bu t-Bu pinB Bpin O O 3 4 83% B2pin2 = B B dtbpy = O O N N Scheme 4.

Scheme 1. Halogenation Br O O [Ir(OMe)cod] NBS OR Ar3P OR + B2pin2 octane, 80°C H Bpin 1 5 F3C B pin , KOAc Bpin Ar3P = P 2 2 Pd cat, ligand F C 3 3

Scheme 2. 6 Scheme 5.

Pd cat, ligand Br + B2pin2 Bpin KOAc Bpin

Scheme 3. B2pin2 pinB 8 [Ir(OMe)cod]2 dtbpy + 80% (1 : 1) cyclohexane action often exhibits different regioselectivity from 80 °C 7 electrophilic halogenation of aromatic systems, since pinB Bpin the steric factor of substrates mainly dominates 9 iridium-catalyzed borylation. In contrast, regioselec- Scheme 6. tivity of halogenation is controlled by the electronic factor via electrophilic substitution. Consequently, iridium-catalyzed direct borylation and palladium- regioselectivity, which is quite different from the catalyzed borylation are often complementary. This conventional electrophilic halogenation to afford 1- feature is beneficial to fabricate functional :-systems bromopyrene 5 (Scheme 5). Now one can access both with substituents at a variety of positions. type of derivatives by the proper choice of function- Borylation of pyrene, perylene, oligoacene alization methods. and corannulene. After unique reactivity and Kobayashi and coworkers further extended selectivity were elucidated with substituted benzenes this protocol to oligoacenes such as antracene and and heteroaromatics, the direct borylation has been tetracene.8) Direct borylation of tetracene 7 provided applied to extended :-conjugated molecules. C–H a 1:1 mixture of 2,8- and 2,9-diborylated tetracenes 8 borylation of polyaromatic hydrocarbons was re- and 9 (Scheme 6). Borylated tetracenes were useful ported by Marder et al. in 2005 (Scheme 4).7) They building blocks for :-conjugated tetracenes for disclosed highly regioselective direct C–H borylation OFET application. Isobe also reported iridium- of naphthalene, pyrene 1 and perylene 3 by the catalyzed C–H borylation of phenacene.9) [Ir(OMe)cod]2/dtbpy catalyst combination. The in- In 2012, Scott et al. found that the addition of teresting feature of this transformation is specific a small amount of potassium tert-butoxide in the No. 1] Transition metal catalyzed borylation of functional :-systems 3

Bpin Ar Ar B2pin2 meso-position [Ir(OMe)cod]2 pinB N N N t-BuOK N E dmbpy Bpin Ar M Ar M E THF N N N N 85 °C pinB E = Br, NO2, CHO, etc. 10 11 Ar 15 Ar 16 Bpin Me Me 70% Scheme 9. dmbpy = N N Ar Ar Scheme 7. pin2B2 Bpin [Ir(cod)OMe]2 N N N N dtbpy -position Ar M Ar M B pin 2 2 N N dioxane N N [IrCl(cod)]2 100 °C bipyridine 82% (M = Ni) Bpin Ar 15 Ar 17 cyclohexane reflux 70% 12 13 Scheme 10. Bpin + the case of meso-unsubstituted porphyrins such as 15 14 10% (Scheme 9). We envisioned the potential of transition metal-catalyzed direct C–H functionalization of Scheme 8. porphyrins because porphyrins have several aromatic Csp2–H bonds. This rather naive idea led us to borylation facilitates equilibrium of the kinetic attempt iridium-catalyzed direct borylation of triar- products to more thermodynamically stable bory- ylporphyrins 15, which actually took place efficiently lated products. With an excess amount of borylating and regioselectively to provide borylated porphyrins 13) agent (B2pin2) and a catalytic amount of t-BuOK, 17 in good to excellent yields (Scheme 10). 1,3,5,7,9-pentaborylated corannulene 11 was ob- Borylation proceeded exclusively at the O-positions. tained in excellent yield through direct borylation Importantly, this type of regioselectivity had never of corannulene 10 (Scheme 7).10) been accomplished by the conventional electrophilic Iridium-catalyzed direct borylation also pro- substitution reactions.14) ceeded on azulene, which is a representative non- Borylated porphyrins are quite useful building benzenoid aromatic hydrocarbon. Murafuji and blocks for the synthesis of novel and exotic porphyrin Sugihara reported C–H borylation of azulene 12 to derivatives,15) which are otherwise difficult to access afford a mixture of 2- and 1-borylated azulenes by the conventional porphyrin synthesis. Borylated 13 and 14 in 70% and 10% yields, respectively porphyrins were employed for preparing porphyrin (Scheme 8).11) oligomers16) with unique shapes and interesting Borylation of porphyrins and related mole- optical properties, highly conjugated porphyrins17) cules. Porphyrins are one of the most important for dye-sensitized solar cell application, cyclometal- functional molecules, which are planar polypyrrole lated porphyrins,18) cyclophane-like diporphyrins19) macrocycle with an 18: distinct aromatic charac- and so forth. For example, tetraborylated porphyrin ter.12) This molecule has its long history of extensive 18 is a key intermediate for construction of a researches covering a wide field of natural sciences. porphyrin tube 20 (Scheme 11).20) The material science related to porphyrin includes In the case of 5,10,15,20-tetraarylporphyrins, artificial photosynthesis, organic solar cells, photo- iridium-catalyzed borylation does not take place on dynamic therapy, light-emitting materials, near- the porphyrin skeleton. The aryl substituents instead infrared dyes, non-linear optical materials, molecular of the porphyrin core can be selectively borylated.21) wires, catalysis, supramolecules and so forth. For example, porphyrin tetramer 21 can be borylated However, functionalization of porphyrin deriva- exclusively on the methoxyphenyl groups to provide tives had been limited to electrophilic substitution diborylated product 22 because 21 has accessible such as halogenation, nitration and formylation, C–H bonds only on the terminal aryl substituents which proceed selectively at the meso-positions in (Scheme 12). This procedure would be useful for 4 H. SHINOKUBO [Vol. 90,

Ar Ar C6F5 C6F5 B2pin2 pinB Bpin [Ir(OMe)cod] Bpin Br N N Br N HN 2 N HN N N N N dtbpy C F C F 6 5 dioxane 6 5 Ni + Ni NH HN NH HN 100 °C N N N N Br N N Br pinB Bpin C6F5 23 91% C6F5 24 Ar 18Ar 19 Scheme 13. Ar

N N C F C F N 6 5 6 5 Ni N Ar N Chloroacetone N C6F5 N N HN N H PdCl2(dppb) N NH Ar 24 N NNi HN Pd2(dba)3, PPh3 Ar N N Cs2CO3 H NH N C6F5 N Cs2CO3, CsF N 82% N C6F5 C6F5 toluene/DMF/H2O NiN N 25 reflux Ar N N C F C F N N 6 5 6 5 Ar N Ni N N N DDQ NH N N HN 10% C6F5 C6F5 Ar 83% 20 N HN NH N Scheme 11. C6F5 26 C6F5

Ar Scheme 14.

N OMe N Zn N Ar Ar N N 21 highly regioselective synthesis of 2-borylated corrole N Zn N 23) N 24, which turned out to be a useful platform for N Ar Ar N functionalization of corroles (Scheme 13). Zn N Ar Ar pinB On the basis of regioselective C–H borylation of N N N Zn N C–H borylation MeO N OMe corrole 23, we synthesized and characterized singly N 95% N Ar Ar Zn and doubly linked corrole dimers 25 and 26 N Ar Ar N N 22 (Scheme 14). The corrole dimer 26 exhibits very N Zn N N N Ar Ar broad absorption bands, which reach to 1700 nm N 24) Zn because of its substantial biradical character. Ar N N N Expanded porphyrins are porphyrin-like :-con- N Zn N MeO N jugated macrocyclic molecules with more than four Ar Ar units.25) Aromatic substituents on expanded pinB porphyrins such as hexaphyrin can be also borylated. Scheme 12. In this case, borylation occurred on 28:-hexaphyrin 27 but not on 26:-hexaphyrin 29 probably because of oxidative nature of 29 (Scheme 15).26) terminal selective functionalization of molecular Synthesis of cyclic tetraindole through direct wires. borylation. Direct C–H borylation is also useful for Corrole is a representative porphyrin analogue the preparation of the intermediate to a porphyrin- with one direct pyrrole–pyrrole linkage.22) Corrole is like cyclic tetraindole 32.27) The synthesis of cyclic also 18: aromatic molecule that exhibits interesting tetraindole 32, which has a similar structure to the optical properties and unique metal coordination porphyrin system, had been quite difficult by conven- chemistry. However, the synthesis of corrole deriva- tional method due to steric repulsion of inner four tives remains rather limited due to lack of regiose- NH protons in the central cavity. We accomplished lective functionalization of corroles. On the basis preparation of this molecule through direct boryla- of iridium-catalyzed C–H borylation, we achieved tion of bisindole 30 as the key step. Iridium-catalyzed No. 1] Transition metal catalyzed borylation of functional :-systems 5

1 1 Ar H Ar Ar2 H Ar2 t-Bu O t-Bu N N pin2B2 t-Bu t-Bu [Ir(cod)OMe]2 N NH dtbpy NH N 1 N N Ar1 Ar Ar2 Ar2 dioxane H Br2, H2O HN N NH N NH HN Br Br 100 °C NH NH H N N 71% N N Ar1 H Ar1 27 Ar2 H Ar2 28 Cl Cl t-Bu t-Bu t-Bu t-Bu O Ar1 = Ar2 = Bpin 32 63% 33

Cl Cl O t-Bu t-Bu

Ar1 Ar1 N pin2B2 N [Ir(cod)OMe] M(OAc)2 N 2 Br M Br NH N dtbpy N Ar1 Ar1 dioxane N N NH

N t-Bu Ar1 Ar1 29 t-Bu O 34 M = Cu, Zn, Ni Scheme 15. Scheme 17.

t-Bu t-Bu R R (pinB)2 Bpin O N O O N O N [Ir(OMe)cod]2 N H dtbpy H 2 5 NH t-BuOMe NH 60 °C 1 6 Br Br Br Br Br 2 30 Br Br 31 12 7 t-Bu t-Bu 8 t-Bu 11 t-Bu O N O O N O Pd (dba) /S-phos N R R 2 3 H Cs2CO3 HN 35 36 NH toluene/DMF H 100 °C N Scheme 18.

t-Bu t-Bu 32 20% (in 2 steps) important class of dyes and pigments for widespread Scheme 16. use.28) Recently, PBI derivatives have received much attention for applications toward organic optelec- tronic materials. The conventional synthesis of PBI C–H borylation of bisindole 30 provided borylated derivatives employs halogenation at the bay area indole 31 in almost quantitative yield. Dimerization (1,6,7,12-positions) to furnish halogenated PBIs of 31 under the Suzuki–Miyaura coupling conditions such as 36 (Scheme 18).29) This is due to the high provided cyclic tetraindole 32 in 20% yield reactivity of the bay area toward electrophilic (Scheme 16). substitutions. Regioselective functionalization at The highly distorted structure of cyclic tetrain- 2,5,8,11-positions of PBIs had been unavailable until dole 32 was elucidated on the basis of X-ray our reports on direct alkylation and arylation of PBIs crystallographic analysis. In addition, 32 was un- at 2,5,8,11-positions by Murai–Chatani–Kakiuchi stable under air. We then found that tetraindole 32 reaction (Scheme 19).30) can be oxidized into a highly planar macrocycle 33 We also accomplished regioselective four-fold through oxidation with bromine (Scheme 17). The C–H borylation of PBI 35 with a [Ir(OMe)cod]2/ 31),32) oxidized macrocycle 34 can capture metal ions such (C6F5)3P catalyst system (Scheme 20). The as Cu(II), Zn(II) and Ni(II) in its porphyrin-like inner boron substituents in borylated PBI 39 can be cavity. The metalated macrocycles 34 exhibited the oxidized to hydroxy groups with hydroxylamine. broad and wide absorption band, which covered over Interestingly, introduction of the hydroxy group the visible region. 2,5,8,11-positions induced substantial blue-shift in Borylation of perylene bisimides. Perylene the UV/vis absorption spectrum due to intramolec- tetracarboxylic acid bisimide (35, PBI) is an ular hydrogen bonding interactions. In addition, 6 H. SHINOKUBO [Vol. 90,

R Bpin O N O

Ar Ar Ar Ar R R B2pin2 [Ir(OMe)cod]2 dtbpy R R mesitylene/t-BuOMe O N O 3) 3 80 °C Ar Ar Ar Ar (CO)(PPh 2 41 88% RuH °C 165 R R Bpin 42 37 O O N O OH O R Ar B O RuH O R Ar Ar Ar Ar 2 (CO)(PPh O N O H2O2 NaOH PIFA 140 3 ) O N O °C 3 Ar Ar R O 35 Ar Ar Ar Ar t-Bu 85% 84% O OH 43O 44

Ar Ar Scheme 21.

O N O 38 R Ar Ar Scheme 19. Ar Bpin Ar OTf

R R R 1) oxidation O N O O N O O N O 2) Tf2O/pyridine pinB Bpin HO OH B2pin2 NH OH•HCl Ar Bpin Ar OTf [Ir(OMe)cod]2 2 NaOH (C6F5)3P 81% 45 dioxane EtOH rt Ar Ar 46 110 °C Ar pinB Bpin HO OH

O N O O N O O N O R R R Ar X 35 3978% 40 82%

Scheme 20.

Ar X borylated PBIs 39 serve as a building block for 47 Ar molecular assemblies on the basis of PBI though X = NHR, OR, CN, aryl, alkynyl palladium-catalyzed cross coupling reaction.33) The substitutions at 2,5,8,11-positions maintain planar Scheme 22. geometry of the perylene :-plane while the conven- tional modification at the bay areas generally induce difficult to prepare by the conventional HBC synthe- molecular distortion due to steric repulsion between sis. In addition, :-extended quinone 44 was synthe- substituents. sized for the first time through oxidation of dihy- Borylation of hexa-peri-hexabenzocoronens. droxy HBC 43. Hexa-peri-hexabenzocoronene (HBC) has attracted Borylation of HBCs allows efficient installation much attention as a fragment of graphene.34) The of various functionalities after construction of the edge structure of graphene results in significant HBC skeleton.36) The boryl groups in borylated HBC changes its physical property. Consequently, effective 45 can be transformed to triflate groups, which are functionalization of HBCs is needed to access model versatile intermediate for further functionalization compounds for functionalized graphenes. (Scheme 22). We demonstrated that iridium-catalyzed direct Borylated boron dipyrrins. Boron dipyrrin borylation of substituted HBC 41 proceeded effi- (BODIPY) is also an important class of :-systems, ciently to furnish borylated HBC 42 in good yield which has wide-spread application in labeling re- (Scheme 21).35) The borylated HBC 42 was success- agents, fluorescent switches, chemosensors, near IR fully converted into hydroxy HBC 43, which is absorbing/emitting dyes and dyes-sensitized solar No. 1] Transition metal catalyzed borylation of functional :-systems 7

Ar B2pin2 Ar Ar Ar Ar B2pin2 Ar [Ir(OMe)cod]2 Pd2(dba)3 dtbpy NBS X-Phos pinB Bpin + Bpin Br Bpin N N dioxane N N N N N N N N KOAc N N B B B B rt B B 100 °C dioxane F F 48 F F 49 F F 50 F F 82% 73% -selective F F 110 °C F F 10% 48 28%

Ar Ar Ar Scheme 25. B2pin2 [Ir(OMe)cod]2 dtbpy + NH HN NH HN NH HN dioxane 52 53 Ar 51 100 °C pinB Bpin Bpin Ar -selective 80% 15% Bpin + Br Br N N N N Scheme 23. B B F F 50 F F 57 (2.4 equiv) Ar F F Ar Pd2(dba)3 B t-Bu3P N N CO2Me Ar Cs2CO3 N N N N [Rh(OH)(cod)]2 B B 49 THF/H2O N N F F 58 Ar F F dioxane/H2O rt rt MeO2C B CO2Me 71% F F 54 1% Scheme 26. Ar

CO2Me [Rh(OH)(cod)]2 1) DDQ N N 52 B 2) BF •OEt /Et N Conclusion dioxane/H2O 3 2 3 F F 100 °C 55 9% MeO2C CO2Me The use of organic molecules for electronic devise has come into reality. In our daily life, we rely on Scheme 24. smart phones and tablets, into which functional organic materials are fabricated. It is quite sure that cells owing to their advantageous photophysical organic materials would further substitute inorganic properties such as photostability, high absorption materials in many ways during this century. To coefficients and high fluorescence quantum yields.37) support this shift, synthesis of the organic materials Functionalization of BODIPY dyes is important should be more efficient, cost-effective and environ- for fine-tuning of the spectroscopic and electronic mentally benign. Direct C–H functionalization properties. should be the key technology to enable the straight- We applied iridium-catalyzed direct borylation forward preparation of organic :-conjugated mole- to BODIPY dye 48 and dipyrromethane 51 cules with excellent optical and electronic functions. (Scheme 23).38) We demonstrated that borylation In this sense, C–H borylation is not still ideal was highly regioselective and complementary. C–H since the boron group is not incorporated in the borylation occurs exclusively at the ,-position for final products and is wasted during the synthesis. dipyrromethane 51 and at the O-positions for Synthetic organic chemists should devote their BODIPY 48. This regioselectivity allows synthesis efforts more to achieve the ideal synthesis of organic of a variety of ,- and O-substituted BODIPY dyes. functional materials. The introduction of unsaturated ester moieties to BODIPY was achieved through rhodium-catalyzed Acknowledgements Heck-type addition (Scheme 24). I am deeply indebted to all of my colleagues for O-Borylated BODIPY 50 was also prepared their enthusiastic contributions and efforts. These through palladium-catalyzed borylation of bromo works were supported by grants-in-aid for Scientific BODIPY 56, which was obtained by regioselective Research from MEXT, Japan. I am also grateful bromination of BODIPY 48 with N-bromosuccini- for the PRESTO project at Japan Science and mide (Scheme 25).39) Although this protocol required Technology Agency. two reaction steps, the total yields were better than those via iridium-catalyzed direct borylation, References as shown in Scheme 23. Borylated BODIPY 50 was employed for the efficient construction of linear 1) Müller, T.J.J. and Bunz, U.H.F. (2007) Functional Organic Materials. Wiley-VCH, Weinheim. BODIPY dimer and trimer 58, which exhibit 2) (a) Murai, S. (1999) Activation of unreactive bonds strong absorption and emission in near IR region and organic synthesis, Springer, Berlin; (b) (Scheme 26). Kakiuchi, F. and Chatani, N. (2003) Catalytic 8 H. SHINOKUBO [Vol. 90,

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sibility. J. Am. Chem. Soc. 134, 15169–15172. (2010) Strategic synthesis of 2,6-pyridylene- 11) Kurotobi, K., Miyauchi, M., Takakura, K., Murafuji, bridged O-to-O porphyrin nanorings through T. and Sugihara, Y. (2003) Direct introduction of a cross-coupling. Chemistry 16, 3009–3012. boryl substituent into the 2-position of azulene: 17) (a) Baba, H., Chen, J.P., Shinokubo, H. and Osuka, application of the Miyaura and Smith methods to A. (2008) Efficient rhodium-catalyzed installation azulene. Eur. J. Org. Chem. 3663–3665. of unsaturated ester functions onto porphyrins: 12) (a) Kadish, K.M., Smith, K.M. and Guilard, R. site-specific Heck-type addition versus conjugate (2000) The Porphyrin Handbook. Vol. 1–10, Aca- addition. Chemistry 14, 4256–4262; (b) Chen, demic Press, San Diego; (b) Kadish, K.M., Smith, J.P., Aratani, N., Shinokubo, H. and Osuka, A. K.M. and Guilard, R. (2003) The Porphyrin (2009) Post-modification of meso–meso-linked Handbook. 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(2011) Palladium-catalyzed O-selective meso directly linked porphyrin dimer sensitizers direct arylation of porphyrins. Angew. Chem. Int. for photovoltaics. J. Phys. Chem. C 113, 21956– Ed. 50, 8867–8870; (b) Tokuji, S., Awane, H., 21963. Yorimitsu, H. and Osuka, A. (2013) Direct 18) (a) Yamaguchi, S., Katoh, T., Shinokubo, H. and arylation of meso-formyl porphyrin. Chemistry Osuka, A. (2007) Porphyrin pincer complexes: 19,64–68; (c) Yamamoto, Y., Tokuji, S., peripherally cyclometalated porphyrins and their Tanaka, T., Yorimitsu, H. and Osuka, A. (2013) catalytic activities controlled by central metals. J. Direct arylation of porphyrins with :-extended Am. Chem. Soc. 129, 6392–6393; (b) Yamaguchi, aryl bromides under ligand-free Fagnou–Hartwig S., Katoh, T., Shinokubo, H. and Osuka, A. (2008) conditions. Asian J. Org. Chem. 2, 320–324. Pt(II)- and Pt(IV)-Bridged cofacial diporphyrins 15) (a) Shinokubo, H. and Osuka, A. (2009) Marriage via carbon-transition metal <-bonds. J. Am. Chem. of porphyrin chemistry with metal-catalysed Soc. 130, 14440–14441; (c) Yamaguchi, S., reactions. Chem. Commun. (Camb.) 1011–1021; Shinokubo, H. and Osuka, A. (2009) Double (b) Hiroto, S., Yamaguchi, S., Shinokubo, H. and cleavage of sp2 C–H and sp3 C–H bonds on one Osuka, A. (2009) Porphyrin derivatives with metal center: DMF-appended cyclometalated plat- carbon-metal bonds. J. Synth. Org. Chem. Jpn. inum(II) and -(IV) porphyrins. Inorg. Chem. 48, 67, 688–700. 795–797; (d) Yamaguchi, S., Shinokubo, H. and 16) (a) Hisaki, I., Hiroto, S., Kim, K.S., Noh, S.B., Kim, Osuka, A. (2010) 22-Porphyrin Ru(II) : complexes. D., Shinokubo, H. and Osuka, A. (2007) Synthesis J. Am. Chem. Soc. 132, 9992–9993; (e) Yoshida, of doubly O-to-O 1,3-butadiyne-bridged diporphyr- K., Yamaguchi, S., Osuka, A. and Shinokubo, H. ins: enforced planar structures and large two- (2010) Platinum(II) and platinum(IV) porphyrin photon absorption cross sections. Angew. Chem. pincer complexes: synthesis, structures, and reac- Int. Ed. 46, 5125–5128; (b) Song, J., Jang, S.Y., tivity. Organometallics 29, 3997–4000; (f ) Yamaguchi, S., Sankar, J., Hiroto, S., Aratani, N., Yoshida, K., Nakashima, T., Yamaguchi, S., Shin, J.Y., Easwaramoorthi, S., Kim, K.S., Kim, Osuka, A. and Shinokubo, H. (2011) Peripherally D., Shinokubo, H. and Osuka, A. (2008) 2,5- cyclometalated iridium complexes of dipyridylpor- Thienylene-bridged triangular and linear porphy- phyrin. Dalton Trans. 40, 8773–8775; (g) rin trimers. Angew. Chem. Int. Ed. 47, 6004–6007; Yamamoto, J., Shimizu, T., Yamaguchi, S., (c) Song, J.X., Aratani, N., Kim, P., Kim, D., Aratani, N., Shinokubo, H. and Osuka, A. (2011) Shinokubo, H. and Osuka, A. (2010) Porphyrin Synthesis of a diimidazolylporphyrin pincer palla- “lego block” strategy to construct directly meso-O dium complex. J. Porphyrins Phthalocyanines 15, doubly linked porphyrin rings. Angew. Chem. Int. 534–538. Ed. 49, 3617–3620; (d) Song, J.X., Aratani, N., 19) Hiroto, S., Hisaki, I., Shinokubo, H. and Osuka, A. Heo, J.H., Kim, D., Shinokubo, H. and Osuka, A. (2008) Synthesis of directly and doubly linked (2010) Directly Pd(II)-bridged porphyrin belts dioxoisobacteriochlorin dimers. J. Am. Chem. Soc. with remarkable curvatures. J. Am. Chem. Soc. 130, 16172–16173. 132, 11868–11869; (e) Song, J.X., Aratani, N., 20) Song, J.X., Aratani, N., Shinokubo, H. and Osuka, Shinokubo, H. and Osuka, A. (2011) A O-to-O 2,5- A. (2010) A porphyrin nanobarrel that encapsu- thienylene-bridged cyclic porphyrin tetramer: its lates C60. J. Am. Chem. Soc. 132, 16356–16357. rational synthesis and 1:2 binding mode with C60. 21) Hata, H., Yamaguchi, S., Mori, G., Nakazono, S., Chem. Sci. 2, 748–751; (f ) Song, J.X., Kim, P., Katoh, T., Takatsu, K., Hiroto, S., Shinokubo, H. Aratani, N., Kim, D., Shinokubo, H. and Osuka, A. and Osuka, A. (2007) Regioselective borylation of 10 H. SHINOKUBO [Vol. 90,

porphyrins by C–H bond activation under iridium Org. Chem. 71, 5051–5066; (d) Langhals, H. catalysis to afford useful building blocks for (2005) Control of the interactions in multichromo- porphyrin assemblies. Chem. Asian J. 2, 849–859. phores: novel concepts. perylene bis-imides as 22) (a) Aviv, I. and Gross, Z. (2007) Corrole-based components for larger functional units. Helv. applications. Chem. Commun. (Camb.) 1987– Chim. Acta 88, 1309–1343. 1999; (b) Gryko, D.T. (2002) Recent advances in 29) (a) Rajasingh, P., Cohen, R., Shirman, E., Shimon, the synthesis of corroles and core-modified corroles. L.J.W. and Rybtchinski, B. (2007) Selective Eur. J. Org. Chem. 1735–1743; (c) Gross, Z. and bromination of perylene diimides under mild Gray, H.B. (2004) Oxidations catalyzed by metal- conditions. J. Org. Chem. 72, 5973–5979; (b) locorroles. Adv. Synth. Catal. 346, 165–170. Handa, N.V., Mendoza, K.D. and Shirtcliff, L.D. 23) Hiroto, S., Hisaki, I., Shinokubo, H. and Osuka, A. 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Harriman, A. (2007) The chemistry of Bodipy: connected BODIPY oligomers through Suzuki– a new El Dorado for fluorescence tools. New J. Miyaura coupling. Org. Lett. 13, 2992–2995; (b) Chem. 31, 496–501. Hayashi, Y., Obata, N., Tamaru, M., Yamaguchi, 38) Chen, J.P., Mizumura, M., Shinokubo, H. and S., Matsuo, Y., Saeki, A., Seki, S., Kureishi, Y., Osuka, A. (2009) Functionalization of boron Saito, S., Yamaguchi, S. and Shinokubo, H. (2012) dipyrrin (BODIPY) dyes through iridium and Facile synthesis of biphenyl-fused BODIPY and its rhodium catalysis: a complementary approach to property. Org. Lett. 14, 866–869. ,- and O-substituted BODIPYs. Chemistry 15, 5942–5949. 39) (a) Hayashi, Y., Yamaguchi, S., Cha, W.Y., Kim, D. (Received Sep. 19, 2013; accepted Nov. 14, 2013) and Shinokubo, H. (2011) Synthesis of directly

Profile

Hiroshi Shinokubo was born in Kyoto in 1969. He received his B.Eng in 1992 and Ph.D. in 1998 from Kyoto University under the guidance of Profs. Kiitiro Utimoto and Koichiro Oshima. He became Assistant Professor in 1995, at Graduate School of Engineering, Kyoto University, working for Prof. Oshima. He worked with Prof. Rick L. Danheiser at MIT from 1999 to 2000 as a visiting scientist. He then collaborated with Prof. Atsuhiro Osuka at Graduate School of Science, Kyoto University, as Associate Professor from 2003 to 2008. He was also selected as a PRESTO researcher at Japan Science and Technology Agency from 2003 to 2007. In 2008, he became Professor at Graduate School of Engineering, Nagoya University. He received the Chemical Society of Japan Award for Young Chemists in 2004, the Minister Award for Distinguished Young Scientists from MEXT in 2008, the JSPS Prize in 2012 and SSOCJ DIC Award for Functional Material Chemistry 2013. He is exploring efficient syntheses of novel organic molecules, which have fascinating structures, properties and functions. His current targets include new porphyrin analogues and large polyaromatic molecules.