Letter pubs.acs.org/macroletters
Chirality-Switchable 2,2′-Bipyridine Ligands Attached to Helical Poly(quinoxaline-2,3-diyl)s for Copper-Catalyzed Asymmetric Cyclopropanation of Alkenes Yukako Yoshinaga, Takeshi Yamamoto,* and Michinori Suginome* Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan S Supporting Information *
ABSTRACT: Helical poly(quinoxaline-2,3-diyl)s copolymers PQXbpy consisting of a coordinating unit, which bears a varied achiral, substituted 2,2′-bipyridyl pendant, and a chiral unit bearing chiral side chains were synthesized and used as a ligand in copper-catalyzed asymmetric cyclopropanation of olefins with diazoacetates, giving up to 91:9 er with high chemical yield. The enantioselection relied on the helical structure of PQXbpy. A single PQXbpy afforded either of a pair of enantiomers with high enantioselectivity by switching its helical sense by changing the reaction solvent from pure toluene to a 3/1 mixture of toluene and 1,1,2-trichloroethane.
chiral scaffold to which 2,2′-bipyridine was noncovalently incorporated.7 We have been engaged in the development of helicalpolymer-based chiral catalysts for asymmetric synthesis,8,9 using poly(quinoxaline-2,3-diyl)s (PQX hereafter) as a general polymer scaffold for the covalent incorporation of achiral catalyst pendants.8 PQX features the formation of a singlehanded, rigid helical structure, whose helical sense depends strongly on the subtle difference in the nature of the solvents.9 To date, we have demonstrated highly enantioselective asymmetric reactions using PQX bearing diarylphosphino8a−e and 4-aminopyrid-3-yl8f pendants in several palladium-catalyzed reactions and nucleophilic organocatalysis. In both macromolecular catalyst systems, chiral polymer conformation provides a chiral reaction environment around the intrinsically achiral pendant groups. However, only two PQX derivatives bearing 2-(diarylphosphino)phenyl or 4-aminopyrid-3-yl pendants have so far been established as highly effective catalysts in asymmetric reactions. It is crucially important to demonstrate the generality of high applicability of the PQX skeleton in asymmetric catalysts by accommodating various pendant groups. We herein report on the application of this molecular
2,2′-Bipyridines have been widely utilized as ligands for transition metals in catalysis as well as in functional materials because of their unique electronic and coordinating properties. Particular attention has focused on the investigation of their chiral variants for use in asymmetric catalysis, although the variety of highly enantioselective chiral-bipyridine-catalyzed reactions is still limited.1 The design of chiral bipyridine ligands mostly relies on the attachment of chiral substituents on the pyridine rings in a C2-symmetrical fashion. In addition to chiral substituents containing point chirality,2 those bearing planar3 and axial chirality4 are utilized to create effective chiral reaction environments around the coordinated metal centers. However, because of the molecular symmetry, along with the tedious synthesis, fine-tuning of the ligand structure is often difficult. It seems likely that C1-symmetrical chiral bipyridine ligands would allow higher flexibility in the molecular design and easier access to a wide variety of ligand structures, although C1-symmetrical bipyridine ligands have seldom afforded high enantioselectivities in catalytic asymmetric reactions.2e−h,k,3a We envisioned that helical macromolecular scaffolds could serve as a platform for incorporation of the 2,2′-bipyridine group as a pendant for use in asymmetric catalysis.5,6 In spite of the C1 symmetry, the huge helical macromolecular structure is expected to provide an effective chiral reaction environment around the coordinated metal centers. The effect of a helical macromolecular structure on 2,2′-bipyridine/copper-mediated asymmetric reactions has been clearly demonstrated recently; natural DNA was used as a © XXXX American Chemical Society
Received: May 11, 2017 Accepted: June 16, 2017
705
DOI: 10.1021/acsmacrolett.7b00352 ACS Macro Lett. 2017, 6, 705−710
Letter
ACS Macro Letters design to chiral 2,2′-bipyridines (Figure 1). Nine derivatives having different 2,2′-bipyridyl groups were synthesized and
Table 1. Synthesis of PQXbpy from PQXboh by Postpolymerization Suzuki−Miyaura Cross-Couplinga
Figure 1. Structural Model of (P)-PQXbpy.
used in the copper-catalyzed asymmetric cyclopropanation of alkenes.2c,h,k,10,11 We found that the substituents on the bipyridyl groups significantly affected the enantioselectivities of the reaction. In addition to high enantioselectivities, the present system features a switch in enantioselection by changing the reaction solvent, by virtue of the solventdependent switch of helical chirality of the PQX skeleton. Various PQXbpys bearing different 2,2′-bipyridyl groups were synthesized from single-handed PQXboh 200mer,9f which carries 10 boronyl-containing units along with 190 chiral units, on average, through Suzuki−Miyaura cross-coupling with 6bromo-2,2′-bipyridines (Table 1). In addition to PQXbpy L1 bearing an unsubstituted 2,2′-bipyridyl, L2−7 bearing various 6′-substituted 2,2′-bipyridyl groups, and L8 and L9 having two or three methyl groups were synthesized in high yields. Complete conversion of the boronyl groups to the corresponding bipyridyl groups was confirmed by 1H NMR spectroscopy. The structure of L8 was further confirmed by 2D NMR analysis (see the Supporting Information, SI). For L7 bearing a 6trifluoromethyl group, the incorporation ratio of the 6trifluoromethyl-2,2′-bipyridyl group was estimated to be at least 90% by 19F NMR analysis (see the SI). All PQXbpys showed identical CD spectra, from which the induction of pure right-handed helical structures was indicated (see the SI). The obtained PQXbpys were used as chiral ligands in the asymmetric Cu-catalyzed cyclopropanation of 1,1-diphenylethene (1a) with diazoacetates (2a). To a catalyst prepared from Cu(OTf)2 (1.25 mol %) and PQXbpy (1.9 mol % bpy units) in chloroform, 1a and 2 were added successively at 0 °C (Table 2). PQXbpy L1 bearing an unsubstituted 2,2′-bipyridine group resulted in the formation of the cyclopropanation product (R)3aa12 with 74:26 er (enantiomeric ratio) albeit in low yield. Carbene dimerization was found to be the side reaction causing lower chemical yield. The yield was later improved by utilizing a slow addition procedure. We then investigated PQXbpys bearing substituents at 6′-position. 6′-Methyl (L2), 6′-propyl (L3), and 6′-isopropyl (L4) derivatives showed much higher er than the unsubstituted PQXbpy L1, affording enantioselectivities around 85:15 er. In contrast, the introduction of the 6′-tbutyl group (L5) along with 6′-methoxy (L6) and 6′trifluoromethyl (L7) groups resulted in much lower enantioselectivities. It should be noted that 4′,6′-dimethyl-2,2′bipyridine derivative L8 showed the highest selectivity among the PQXbpys examined, while the additional introduction of a 4-methyl group (L9) resulted in much lower enantioselectivity. These results clearly suggest that substituents on the bipyridine ring significantly alter the enantioselectivity of the reaction and
ligand
yieldb (%)
Mn/104c
Mw/Mnc
gabs × 103d
L1 L2 L3 L4 L5 L6 L7 L8 L9
93 93 90 91 91 82 95 74 89
6.7 7.8 7.3 7.4 7.3 8.1 6.9 7.4 6.6
1.15 1.30 1.18 1.15 1.19 1.34 1.11 1.13 1.16
2.53 2.59 2.65 2.55 2.48 2.54 2.59 2.47 2.49
a
Reaction conditions: PQXboh (1 equiv B), 6-bromobipyridyl derivatives (10 equiv), Pd(PPh3)4 (10 mol %), Na2CO3 (3 equiv) in THF/H2O (5/1), at 110 °C for 30 h. bIsolated yield. cDetermined by GPC analysis. dKuhn’s dissymmetry factor gabs at 369.5 nm, in chloroform at 20 °C.
that L8 is the chiral ligand of choice in the asymmetric cyclopropanation reaction. Further optimization of the reaction conditions indicated that the reaction should be carried out at −20 °C in toluene with slow addition of diazoacetate (2.2 equiv) using 2.5 mol % Cu(OTf)2 with 3.0 mol % L8 and 3.0 mol % phenylhydrazine (see the SI). Under these reaction conditions, reaction of 1a with 2a afforded 3aa in 95% yield with 91:9 er (Table 3, entry 1). Use of p-methoxybenzyl, 2-naphthylmethyl, and 3,5bis(trifluoromethyl)benzyldiazoacetates resulted in slightly lower ers (87:13−89:11; entries 2−4), although the use of the bulky 2,4,6-trimethylbenzyl ester resulted in low er (entry 5). Phenyl and 2-phenylethyl dizoacetates afforded high enantioselectivities, comparable to the benzyl diazoacetate (entries 6 and 7). t-Butyl ester also afforded high enantioselectivity (entry 8). Other alkenes were also subjected to the cyclopropanation. 1,1-Diarylethenes 1b,c afforded the corresponding cyclopropane derivatives with good enentioselectivities, around 90:10 er (entries 9 and 10). Reactions of 706
DOI: 10.1021/acsmacrolett.7b00352 ACS Macro Lett. 2017, 6, 705−710
Letter
ACS Macro Letters Table 2. Asymmetric Cyclopropanation of 1,1Diphenylethene 1a with Benzyl Diazoacetate in the Presence of PQXbpy L1−9a
ligand
yieldb (%)
erc
L1 L2 L3 L4 L5 L6 L7 L8 L9
16 34 44 46 23 30 22 34 30
74:26 85:15 86:14 83:17 53:47 64:36 64:36 88:12 66:34
Table 4. Asymmetric Cyclopropanation of Styrenes 1 with Diazoacetate 2 in the Presence of PQXbpy L8a
entry
Ar
3
yieldb (%) cis/trans
erc (%) cis/trans
1 2 3
Ph 1-naphtyl mesityl
3da 3ea 3fa
37/49 41/35 62/36
73:27/73:27 78:22/76:24 87:13/87:13
Reaction conditions: Cu(OTf)2 (2.5 μmol) and (P)-(R)-L8 (3.0 μmol) were stirred in THF (500 μL). The solvent was evaporated in vacuo. After addition of toluene (500 μL), phenylhydrazine (0.10 M in toluene, 30 μL, 3.0 μmol), and 1 (0.1 mmol), a solution of 2 (0.22 mmol) in toluene (150 μL) was slowly added over 12 h at −20 °C, and the mixture was stirred for 1 h. bNMR yield. cDetermined by chiral SFC analysis. a
Reaction conditions: Cu(OTf)2 (1.25 μmol) and (P)-(R)-PQXbpy (1.9 μmol) were stirred in THF (500 μL) for 1 h. The solvent was evaporated in vacuo. Chloroform (500 μL), phenylhydrazine (0.05 M in chloroform, 30 μL, 1.5 μmol), 1 (0.1 mmol), and a solution of 2 (0.22 mmol) in chloroform (150 μL) were added, and the mixture was stirred at 0 °C for 1 h. bNMR yield. cDetermined by chiral SFC analysis.
We used PQXbpy with inverted helical chirality in the cyclopropanation reaction (Scheme 1). The right-handed (P)(R)-PQXbpy L8 was dissolved in a mixture of toluene and 1,1,2-trichloroethane (1,1,2-TCE; 3/1) and stirred at room temperature for 6 h. CD spectra showed complete inversion of the helical sense to the left-handed structure (Scheme 1a). The
Table 3. Asymmetric Cyclopropanation of 1,1-Diarylethenes 1 with Diazoacetate 2 in the Presence of PQXbpy L8a
Scheme 1. (a) CD Spectra of L8 in Various Solvents at 20 °C; (b) Use of L8 with Inverted Helical Chirality in Asymmetric Cyclopropanation of 1 with 2
a
entry
R1
R2
3
yieldb (%)
erc
1 2 3 4 5 6 7 8 9 10
Ph Ph Ph Ph Ph Ph Ph Ph p-Tol p-FC6H5
Bn p-MeOC6H4CH2 2-NapCH2 3,5-(CF3)2C6H3CH2 2,4,6-Me3C6H2CH2 Ph PhCH2CH2 t-Bu Bn Bn
3aa 3ab 3ac 3ad 3ae 3af 3ag 3ah 3ba 3ca
95 94 52 83 81 93 95 71 92 88
91:9 89:11 88:12 87:13 63:37 90:10 90:10 89:11 90:10 89:11
Reaction conditions: Cu(OTf)2 (2.5 μmol) and (P)-(R)-L8 (3.0 μmol bpy) were stirred in THF (500 μL). The solvent was evaporated in vacuo. After addition of toluene (500 μL), phenylhydrazine (0.10 M in toluene, 30 μL, 3.0 μmol), and 1 (0.1 mmol), a solution of 2 (0.22 mmol) in toluene (150 μL) was slowly added over 12 h at −20 °C, and the mixture was stirred for 1 h. bNMR yield. cDetermined by chiral SFC analysis. a
styrene (1d) and 1-vinylnaphthalene (1e) resulted in the formation of cis and trans isomers, which showed comparable enantiomeric ratios (Table 4). Reaction of 2,4,6-trimethylstyrene preferentially afforded the cis diastereomer in a 62/36 ratio with 87:13 er for both isomers. These results indicated that the PQX scaffold provides an effective chiral reaction environment around the copper to discriminate the chirality α to the ester group. 707
DOI: 10.1021/acsmacrolett.7b00352 ACS Macro Lett. 2017, 6, 705−710
Letter
ACS Macro Letters
(2) 2,2′-Bipyridine bearing point chirality: (a) Hopkins, R. B.; Hamilton, A. D. Iron(III) Complexes of Chiral Bipyridine Macrocycles as Novel Metallo-catalysts. J. Chem. Soc., Chem. Commun. 1987, 3, 171. (b) Bolm, C.; Zehnder, M.; Bur, D. Optically Active Bipyridines in Asymmetric Catalysis. Angew. Chem., Int. Ed. Engl. 1990, 29, 205. (c) Ito, K.; Tabuchi, S.; Katsuki, T. Synthesis of New Chiral Bipyridine Ligands and Their Application to Asymmetric Cyclopropanation. Synlett 1992, 34, 2661. (d) Nishiyama, H.; Yamaguchi, S.; Park, S.-B.; Itoh, K. New Chiral Bis(oxazolinyl)bipyridine Ligand (Bipymox): Enantioselection in the Asymmetric Hydrosilylation of Ketones. Tetrahedron: Asymmetry 1993, 4, 143. (e) Collomb, P.; von Zelewsky, A. Synthesis of new chiral catalysts, pyridyl- and bipyridylalcohols, for the enantioselective addition of diethylzinc to benzaldehyde. Tetrahedron: Asymmetry 1998, 9, 3911. (f) Chelucci, G.; Pinna, G. A.; Saba, A. Enantioselective palladium catalyzed allylic substitution with 2,2′-bipyridine ligands. Tetrahedron: Asymmetry 1998, 9, 531. (g) Kwong, H.-L.; Lee, W.-S. New chiral 2,2′-bipyridine diols as catalysts for enantioselective addition of diethylzinc to benzaldehyde. Tetrahedron: Asymmetry 1999, 10, 3791. (h) Malkov, A. V.; Baxendale, I. R.; Bella, M.; Langer, V.; Fawcett, J.; Russell, D. R.; Mansfield, D. J.; Valko, M.; Kočovský, P. Synthesis of New Chiral 2,2′Bipyridyl-Type Ligands, Their Coordination to Molybdenum(0), Copper(II), and Palladium(II), and Application in Asymmetric Allylic Substitution, Allylic Oxidation, and Cyclopropanation. Organometallics 2001, 20, 673. (i) Kobayashi, S.; Ogino, T.; Shimizu, H.; Ishikawa, S.; Hamada, T.; Manabe, K. Bismuth Triflate-Chiral Bipyridine Complexes as Water-Compatible Chiral Lewis Acids. Org. Lett. 2005, 7, 4729. (j) Azoulay, S.; Manabe, K.; Kobayashi, S. Catalytic Asymmetric Ring Opening of meso-Epoxides with Aromatic Amines in Water. Org. Lett. 2005, 7, 4593. (k) Lyle, M.P. A.; Draper, N. D.; Wilson, P. D. Synthesis and evaluation of new chiral nonracemic C2symmetric and unsymmetric 2,2′-bipyridyl ligands. Org. Biomol. Chem. 2006, 4, 877. (l) Kitanosono, T.; Ollevier, T.; Kobayashi, S. Iron- and Bismuth-Catalyzed Asymmetric Mukaiyama Aldol Reactions in Aqueous Media. Chem. - Asian J. 2013, 8, 3051. (m) Gao, X.; Wu, B.; Huang, W.-X.; Chen, M.-W.; Zhou, Y.-G. Enantioselective Palladium-Catalyzed C−H Functionalization of Indoles Using an Axially Chiral 2,2′-Bipyridine Ligand. Angew. Chem., Int. Ed. 2015, 54, 11956. (n) Kitanosono, T.; Zhu, L.; Liu, C.; Xu, P.; Kobayashi, S. An Insoluble Copper(II) Acetylacetonate−Chiral Bipyridine Complex that Catalyzes Asymmetric Silyl Conjugate Addition in Water. J. Am. Chem. Soc. 2015, 137, 15422. (o) Zhu, L.; Kitanosono, T.; Xu, P.; Kobayashi, S. Cu(II)-Catalyzed asymmetric boron conjugate addition to α,β-unsaturated imines in water. Chem. Commun. 2015, 51, 11685. (p) Kitanosono, T.; Miyo, M.; Kobayashi, S. A Cu(II)-based strategy for catalytic enantioselective β-borylation of α,β-unsaturated acceptors. ACS Sustainable Chem. Eng. 2016, 4, 6101. (3) 2,2′-Bipyridine bearing planar chirality: (a) Wörsdörfer, U.; Vögtle, F.; Nieger, M.; Waletzke, M.; Grimme, S.; Glorius, F.; Pfaltz, A. A New Planar Chiral Bipyridine Ligand. Synthesis 1999, 4, 597. (b) Rios, R.; Liang, J.; Lo, M. M.-C.; Fu, G. C. Synthesis, resolution and crystallographic characterization of a new C2-symmetric planarchiral bipyridine ligand: application to the catalytic enantioselective cyclopropanation of olefins. Chem. Commun. 2000, 5, 377. (4) 2,2′-Bipyridine bearing axial chirality: Wong, H. L.; Tian, Y.; Chan, K. S. Electronically controlled asymmetric cyclopropanation catalyzed by a new type of chiral 2,2′-bipyridine. Tetrahedron Lett. 2000, 41, 7723. (5) Chiral macromolecules: (a) Cornelissen, J. J. L. M.; Rowan, A. E.; Nolte, R. J. M.; Sommerdijk, N. A. J. M. Chiral Architectures from Macromolecular Building Blocks. Chem. Rev. 2001, 101, 4039. (b) Nakano, T.; Okamoto, Y. Synthetic Helical Polymers: Confirmation and Function. Chem. Rev. 2001, 101, 4013. (c) Huc, I. Aromatic Oligoamide Foldamers. Eur. J. Org. Chem. 2004, 1, 17. (d) Yashima, E.; Maeda, K.; Iida, H.; Furusho, Y.; Nagai, K. Helical Polymers: Synthesis, Structures, and Functions. Chem. Rev. 2009, 109, 6102. (e) Yashima, E.; Ousaka, N.; Taura, D.; Shimomura, K.; Ikai, T.; Maeda, K. Supramolecular Helical Systems: Helical Assemblies of
thus obtained (M)-(R)-PQXbpy L8 was used in the reaction of 1a and 2a under the same reaction conditions to right-handed (P)-(R)-L8, except for the use of a 3/1 mixture of toluene and 1,1,2-TCE as solvent. The reaction provided cyclopropanation product 3aa, whose absolute configuration is opposite to the one obtained with right-handed (P)-(R)-L8 in toluene. Notably, the er (9:91) was exactly the same as that obtained with (P)-(R)-L8 (91:9 er), suggesting that the high enantioselectivity arises exclusively from the main chain chirality of PQX. The same level of switch in enantioselection was observed in the reaction of 3ab. In conclusion, we synthesized PQX bearing various 2,2′bipyridyl pendants for use in the copper-catalyzed cyclopropanation reaction. A significant effect of the substituents of the bipyridine rings on the enantioselectivity was observed, leading us to the choice of PQXbpy bearing 4′,6′-dimethyl-2,2′bipyridine pendants as the optimal ligand. Even though the bipyridine groups have C1 symmetry, high enantioselectivities up to 91:9 er were obtained. Our results clearly suggest that the PQX skeleton provides an effective chiral reaction environment to the catalytically active copper metal center. Inversion of the helical chirality of the catalyst was attained by using a 1,1,2TCE-based solvent, providing an opportunity to obtain both enantiomers using a single chiral catalyst. Application of the new macromolecular bipyridine ligand system to other transition metals in catalysis is currently underway in our laboratory.
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsmacrolett.7b00352. Experimental details and characterization data of the products (PDF).
■
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Takeshi Yamamoto: 0000-0002-5184-7493 Michinori Suginome: 0000-0003-3023-2219 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by JSPS KAKENHI Grant Number JP15H05811 in Precisely Designed Catalysts with Customized Scaffolding.
■
REFERENCES
(1) Reviews for chiral 2,2′-bipyridine ligands for asymmetric catalysis: (a) Chelucci, G.; Thummel, R. P. Chiral 2,2′-Bipyridines, 1,10Phenanthrolines, and 2,2′:6′,2″-Terpyridines: Syntheses and Applications in Asymmetric Homogeneous Catalysis. Chem. Rev. 2002, 102, 3129. (b) Fletcher, N. C. Chiral 2,2′-bipyridines: ligands for asymmetric induction. J. Chem. Soc., Perkin Trans. 1. 2002, 16, 1831. (c) Kwong, H.-L.; Yeung, H.-L.; Yeung, C.-T.; Lee, W.-S.; Lee, C.-S.; Wong, W.-L. Chiral pyridine-containing ligands in asymmetric catalysis. Coord. Chem. Rev. 2007, 251, 2188. 708
DOI: 10.1021/acsmacrolett.7b00352 ACS Macro Lett. 2017, 6, 705−710
Letter
ACS Macro Letters
noxaline-Based Phosphines. Angew. Chem., Int. Ed. 2011, 50, 8844. (c) Akai, Y.; Yamamoto, T.; Nagata, Y.; Ohmura, T.; Suginome, M. Enhanced Catalyst Activity and Enantioselectivity with ChiralitySwitchable Polymer Ligand PQXphos in Pd-Catalyzed Asymmetric Silaborative Cleavage of meso-Methylenecyclopropanes. J. Am. Chem. Soc. 2012, 134, 11092. (d) Yamamoto, T.; Akai, Y.; Suginome, M. Chiral Palladacycle Catalysts Generated on a Single-Handed Helical Polymer Skelton for Asymmetric Arylative Ring Opening of 1,4Epoxy-1,4-dihydronaphthalene. Angew. Chem., Int. Ed. 2014, 53, 12785. (e) Akai, Y.; Konnert, L.; Yamamoto, T.; Suginome, M. Asymmetric Suzuki−Miyaura cross-coupling of 1-bromo-2-naphthoates using the helically chiral polymer ligand PQXphos. Chem. Commun. 2015, 51, 7211. (f) Yamamoto, T.; Murakami, R.; Suginome, M. Single-Handed Helical Poly(quinoxaline-2,3-diyl)s Bearing Achiral 4-Aminopyrid-3-yl Pendants as Highly Enantioselective, Reusable Chiral Nucleophilic Organocatalysts in the Steglich Reaction. J. Am. Chem. Soc. 2017, 139, 2557. (9) (a) Nagata, Y.; Yamada, T.; Adachi, T.; Akai, Y.; Yamamoto, T.; Suginome, M. Solvent-Dependent Switch of Helical Main-Chain Chirality in Sergeants-and-Soldiers-Type Poly(quinoxaline-2,3-diyl)s: Effect of the Position and Structures of the “Sergeant” Chiral Units on the Screw-Sense Induction. J. Am. Chem. Soc. 2013, 135, 10104. (b) Nagata, Y.; Kuroda, T.; Takagi, K.; Suginome, M. Ether Solventinduced Chirality Inversion of Helical Poly(quiunoxaline-2,3-diyl)s Containing L-Lactic Acid Derived Side Chains. Chem. Sci. 2014, 5, 4953. (c) Nagata, Y.; Nishikawa, T.; Suginome, M. Poly(quinoxaline2,3-diyl)s Bearing (S)-3-Octylmethyl Side Chains as an Efficient Amplifier of Alkene Solvent Effect Leading to Switch of Main Chain Helical Chirality. J. Am. Chem. Soc. 2014, 136, 15901. (10) Reviews for asymmetric cyclopropanation: (a) Doyle, M. P.; Protopopova, M. N. New aspects of catalytic asymmetric cyclopropanation. Tetrahedron 1998, 54, 7919. (b) Pellissier, H. Recent developments in asymmetric cyclopropanation. Tetrahedron 2008, 64, 7041. (c) Caballero, A.; Prieto, A.; Díaz-Requejo, M. M.; Pérez, P. J. Metal-Catalyzed Olefin Cyclopropanation with Ethyl Diazoacetate: Control of the Diastereoselectivity. Eur. J. Inorg. Chem. 2009, 9, 1137. (d) Bartoli, G.; Bencivenni, G.; Dalpozzo, R. Asymmetric Cyclopropanation Reactions. Synthesis 2014, 46, 979. (11) Cyclopropanation using diazo compounds with metal catalysis: (a) Nozaki, H.; Moriuti, S.; Takaya, H.; Noyori, R. Asymmetric Induction in Carbenoid Reaction by Means of a Dissymmetric Copper Chelate. Tetrahedron Lett. 1966, 7, 5239. (b) Doyle, M. P.; Bagheri, V.; Wandless, T. J.; Harn, N. K.; Brinker, D. A.; Eagle, C. T.; Loh, K.-L. Exceptionally High Trans (Anti) Stereoselectivity in Catalytic Cyclopropanation Reactions. J. Am. Chem. Soc. 1990, 112, 1906. (c) Nishiyama, H.; Itoh, Y.; Matsumoto, H.; Park, S.-B.; Itoh, K. New Chiral Ruthenium Bis(oxazolinyl)pyridine Catalyst. Efficient Asymmetric Cyclopropanation of Olefins with Diazoacetates. J. Am. Chem. Soc. 1994, 116, 2223. (d) Puglisi, A.; Benaglia, M.; Annunziata, R. Bologna, A. Enantiomerically pure phenanthroline or bipyridine containing macrocycles: a new class of ligands for asymmetric catalysis. Tetrahedron Lett. 2003, 44, 2947. (e) Estevan, F.; Lloret, J.; Sanaú, M.; Ú beda, M. A. Enantio- and Diastereocontrol in Intermolecular Cyclopropanation Reaction of Styrene Catalyzed by Dirhodium(II) Complexes with Bulky ortho-Metalated Aryl Phosphines: Catalysis in Water as Solvent. Study of a (+)-Nonlinear Effect. Organometallics 2006, 25, 4977. (f) Uchida, T.; Katsuki, T. α-Diazoacetates as Carbene Precursors: Metallosalen-Catalyzed Asymmetric Cyclopropanation. Synthesis 2006, 10, 1715. (g) Lindsay, V. N. G.; Fiset, D.; Gritsch, P. J.; Charette, A. B. Stereoselective Rh2(S-IBAZ)4-Catalyzed Cyclopropanation of Alkenes, Alkynes, and Allenes: Asymmetric Synthesis of Diacceptor Cyclopropylphosphonates and Alkylidenecyclopropanes. J. Am. Chem. Soc. 2013, 135, 1463. (h) Negretti, S.; Cohen, C. M.; Chang, J. J.; Guptill, D. M.; Davies, H. M. L. Enantioselective dirhodium(II)-catalyzed cyclopropanations with trimethylsilylethyl and trichloroethyl aryldiazoacetates. Tetrahedron 2015, 71, 7415. (i) Chanthamath, S.; Iwasa, S. Enantioselective Cyclopropanation of a Wide Variety of Olefins Catalyzed by Ru(II)-Pheox Complexes. Acc. Chem. Res. 2016, 49, 2080.
Small Molecules, Foldamers, and Polymers with Chiral Amplification and Their Functions. Chem. Rev. 2016, 116, 13752. (6) Helical polymer for asymmetric catalysis: (a) Yashima, E.; Maeda, Y.; Okamoto, Y. Synthesis of Poly[N-(4-ethynylbenzyl)ephedrine] and Its Use as a Polymeric Catalyst fot Enantioselective Addition of Dialkylzincs to Benzaldehyde. Polym. J. (Tokyo, Jpn.) 1999, 31, 1033. (b) Reggelin, M.; Schultz, M.; Holbach, M. Helical Chiral Polymers without Additional Stereogenic Units: A New Class of Ligands in Asymmetric Catalysis. Angew. Chem., Int. Ed. 2002, 41, 1614. (c) Reggelin, M.; Doerr, S.; Klussmann, M.; Schultz, M.; Holbach, M. Helically chiral polymers: A class of ligands for asymmetric catalysis. Proc. Natl. Acad. Sci. U. S. A. 2004, 101, 5461. (d) Hasegawa, T.; Furusho, Y.; Katagiri, H.; Yashima, E. Enantioselective Synthesis of Complementary Double-Helical Molecules that Catalyze Asymmetric Reactions. Angew. Chem., Int. Ed. 2007, 46, 5885. (e) Miyabe, T.; Hase, Y.; Iida, H.; Maeda, K.; Yashima, E. Synthesis of Functional Poly(phenyl isocyanide)s with Macromolecular Helicity Memory and Their Use as Asymmetric Organocatalysts. Chirality 2009, 21, 44. (f) Terada, K.; Masuda, T.; Sanda, F. Asymmetric Reduction of Aromatic Ketimines in the Presence of Helical Polyner as Catalyst. J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 4971. (g) Megens, R. P.; Roelfes, G. Asymmetric Catalysis with Helical Polymers. Chem. - Eur. J. 2011, 17, 8514. (h) Ikeda, A.; Terada, K.; Shiotsuki, M.; Sanda, F. Synthesis of Polymers Bearing Proline Moieties in the Side Chains and Their Application as Catalysts for Asymmetric Induction. J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 3783. (i) Itsuno, S. Polymeric Chiral Catalyst Design and Chiral Polymer Synthesis; John Wiley and Sons: Hoboken, NJ, 2011; pp 223−266. (j) Miyake, G. M.; Iida, H.; Hu, H.Y.; Tang, Z.; Chen, E. Y.-X.; Yashima, E. Synthesis of Helical Poly(phenylacetylene)s Bearing Cinchona Alkaloid Pendants and Their Application to Asymmetric Organocatalysis. J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 5192. (k) Tang, Z.; Iida, H.; Hu, H.-Y.; Yashima, E. Remarkable Enhancement of the Enantioselectivity of an Organocatalyzed Asymmetric Henry Reaction Assisted by Helical Poly(phenylacetylene)s Bearing Cinchona Alkaloid Pendants via an Amide Linkage. ACS Macro Lett. 2012, 1, 261. (l) Zhang, D.; Ren, C.; Yang, W.; Deng, J. Helical Poymer as Mimetic Enzyme Catalyzing Asymmetric Aldol Reaction. Macromol. Rapid Commun. 2012, 33, 652. (m) Itsuno, S.; Hassan, M. M. Polymer-immobilized chiral catalysts. RSC Adv. 2014, 4, 52023. (n) Ousaka, N.; Yamaguchi, T.; Yashima, E. Remarkable Enhancement of Stability and Helix-sense Excess of Oligo(phenylene ethynylene) Foldamers Assisted by Linking with Achiral (Metallo)salen Tethers and Their Application to Asymmetric Catalysis. Chem. Lett. 2014, 43, 512. (o) Wang, H.; Zhang, N. L. J.; Wan, X. Synthesis and Properties of a Novel Pyridineoxazoline Containing Optically Active Helical Polymer as a Catalyst Ligand for Asymmetric Diels-Alder Reaction. Chirality 2015, 27, 523. (p) Zhang, H.; Deng, J. Helical Polymers Showing Inverse Helicity and Synergistic Effect in Chiral Catalysis: Catalytic Functionality Determining Enantioconfiguration and Helical Frameworks Providing Asymmetric Microenvironment. Macromol. Chem. Phys. 2016, 217, 880. (7) (a) Roelfes, G.; Feringa, B. L. DNA-Based Asymmetric Catalysis. Angew. Chem., Int. Ed. 2005, 44, 3230. (b) Boersma, A. J.; Megens, R. P.; Feringa, B. L.; Roelfes, G. DNA-based asymmetric catalysis. Chem. Soc. Rev. 2010, 39, 2083. (c) Boersma, A. J.; Conquière, D.; Geerdink, D.; Rosati, F.; Feringa, B. L.; Roelfes, G. Chiral information harvesting in dendric metallopeptides. Nat. Chem. 2010, 2, 991. (d) G.Fernández, A.; Megens, R. P.; Villarino, L.; Roelfes, G. DNAAccelerated Copper Catalysis of Friedel-Crafts Conjugate Addition/ Enantioselective Protonation Reactions in Water. J. Am. Chem. Soc. 2016, 138, 16308. (8) (a) Yamamoto, T.; Yamada, T.; Nagata, Y.; Suginome, M. HighMolecular-Weight Polyquinoxaline-Based Helically Chiral Phosphine (PQXphos) as Chirality-Switchable, Reusable, and Highly Enantioselective Monodentate Ligand in Catalytic Asymmetric Hydrosilylation of Styrenes. J. Am. Chem. Soc. 2010, 132, 7899. (b) Yamamoto, T.; Akai, Y.; Nagata, Y.; Suginome, M. Highly-Enantioselective Synthesis of Axially Chiral Biarylphosphonates: Asymmetric Suzuki−Miyaura Coupling Using High-Molecular-Weight, Helically Chiral Polyqui709
DOI: 10.1021/acsmacrolett.7b00352 ACS Macro Lett. 2017, 6, 705−710
Letter
ACS Macro Letters (12) Absolute configuration of product 3aa was determined by hydrolysis and comparing its optical rotation with the data shown in: (a) Walborsky, H. M.; Pitt, C. G. Cyclopropanes. XIII. The Absoute Configuration of 1-Methyl-2,2-diphenylcyclopropane. J. Am. Chem. Soc. 1962, 84, 4831. (b) Walborsky, H. M.; Impastato, F. J. Cyclopropanes. VI. Retention of Optical Activity and Configuration in the Cyclopropyl Carbanion. J. Am. Chem. Soc. 1959, 81, 5835.
710
DOI: 10.1021/acsmacrolett.7b00352 ACS Macro Lett. 2017, 6, 705−710
