Perfluorinated Aryls in the Design of Chiral Brønsted Acid Catalysts

Research Article pubs.acs.org/acscatalysis

Perfluorinated Aryls in the Design of Chiral Brønsted Acid Catalysts: Catalysis of Enantioselective [4 + 2] Cycloadditions and Ene Reactions of Imines with Alkenes by Chiral Mono-Phosphoric Acids with Perfluoroaryls Norie Momiyama,*,†,‡ Hiroshi Okamoto,# Jun Kikuchi,#,§ Toshinobu Korenaga,∥ and Masahiro Terada*,#,⊥ †

Institute for Molecular Science, Okazaki, Aichi 444-8787, Japan SOKENDAI (The Graduate School for Advanced Studies), Okazaki, Aichi 444-8787, Japan # Department of Chemistry, Graduate School of Science, and ⊥Analytical Center for Giant Molecules, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan § Graduate Research on Cooperative Education Program of IMS with Tohoku University, Okazaki, Aichi 444-8787, Japan ∥ Department of Chemistry and Bioengineering, Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551, Japan ‡

S Supporting Information *

ABSTRACT: Perfluorinated aryl-incorporating chiral monophosphoric acids were used for highly stereoselective reactions of N-acyl and N-acyloxy aldimines with styrenes. Their electronic and steric profiles were established in comparison with those of phenyl, binaphthyl, and partially fluorinated aryls. The [4 + 2] cycloaddition reactions of N-benzoyl aldimines with alkenes proceeded with excellent diastereo- and enantioselectivities in the presence of the perfluorophenyl-incorporating chiral monophosphoric acid catalysts 1a and 1c. The stereoselective elaboration of polysubstituted cycloadducts to amines is described. The imino−ene reactions of N-Fmoc imines with alkenes have been successfully developed in a three-component manner. This process uses aldehydes, 9-fluorenylmethyl carbamate, and alkenes in the presence of a chiral monophosphoric acid catalyst, 2a, possessing an F10binaphthyl skeleton. KEYWORDS: asymmetric catalysis, chiral Brønsted acid, perfluorinated aryls, cycloaddition, imino−ene reaction

1. INTRODUCTION Perfluorinated aryls are useful in the design of molecular catalysts. Their electronic and steric alterations lead to notable changes in the chemical yields and the stereoselectivities of reactions involving these catalysts.1,2 Unfortunately, the full

potential of perfluorinated aryls has not been exploited in the development of chiral Brønsted acid catalysts.3 We have previously reported the monophosphoric acids 1a4 and 2a,5 which incorporate perfluorinated aryls, as stronger chiral Brønsted acid catalysts than the chiral monophosphoric acid 3 (Figure 1). In 1a and 2a, the electron-withdrawing nature of the perfluoroaryl groups leads to higher Brønsted acidity,6 and 1a is a robust catalyst in the Hosomi−Sakurai reaction of N-acyl imines.4 Notably, 1a initiated this reaction even when less nucleophilic allyl- and crotyl trimethylsilanes, which do not possess a hydrogen bond donor site (Figure 2a upper reaction scheme), were used.7,8 Based on previous results, we decided to explore whether the chiral monophosphoric acids incorporating perfluoroaryls,9 which are stronger chiral Brønsted

Figure 1. Chiral monophosphoric acids. (a) 3,3′-Fluorinated arylincorporated chiral monophosphoric acid 1a. (b) Chiral monophosphoric acid with F10binaphthyl 2a. (c) 3,3′-Aryl-substituted chiral monophosphoric acid 3. © XXXX American Chemical Society

Received: September 24, 2015 Revised: January 3, 2016

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DOI: 10.1021/acscatal.5b02136 ACS Catal. 2016, 6, 1198−1204

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ACS Catalysis

Table 2. Optimization of Catalyst Substituents at 3,3′-Position and N-Benzoyl Substituents on the Iminea

Figure 2. Schematics of reactions in the present study. (a) Less reactive nucleophiles in previous and this study. (b) Highly reactive nucleophiles in previous reports.

acid catalysts,10−13 can be used in reactions with other less reactive alkenes (Figure 2a lower reaction scheme).5 The reaction of N-acyl or N-acyloxy imines with styrenes allows ready access not only to substituted homoallylic amine derivatives14 but also to highly substituted heterocycles.15 Although a variety of chiral monophosphoric acids, 3, have been shown to catalyze enantioselective reactions of imines (Figure 2b),16 there are no successful examples of the control of enantioselective processes using styrenes as nucleophiles.17 Therefore, this presented an attractive opportunity to investigate the effect of perfluoroaryls on these reactions and establish them as versatile tools in the design of chiral Brønsted acid catalysts. Herein, we provide a detailed study on the catalytic

entry

catalyst

Ar in 4

yield (%)b

ee (%)c

cis:transd

1 2 3 4 5 6e,e 7e,f 8e,f

1a 1b 1c 3a 1a 1a 1a 1c

Ph Ph Ph Ph 3,5-F2C6H3 3,5-F2C6H3 3,5-F2C6H3 3,5-F2C6H3

81 43 67 27 95 86 95 90

80 −8 80 20 97 98 98 99

>20:1 8:1 >20:1 7:1 >20:1 >20:1 >20:1 >20:1

a

Reactions were conducted with 1.1 equiv of 4 and 1.0 equiv of 5a in the presence of 10 mol % 1 in toluene at 40 °C. bIsolated yield. c Determined by chiral HPLC. dDetermined by 1H NMR analysis. e At 0 °C. f5 mol % of 1.

performance of perfluoroaryl-incorporated monophosphoric acids 1 and 2 in the catalytic enantioselective [4 + 2] cycloaddition and imino−ene reactions.

Table 1. Chiral Mono-Phosphoric Acid-Catalyzed Enantioselective Reaction of N-Acyl or N-Acyloxy Imines with Alkenesa

entry

catalyst

(mol %)

−(CO)G

product

yield (%)b

ee (%)c

cis:transd

1 2 3 4 5 6e 7

1a 2a 3a 1a 1a 2a 3a

(10) (10) (10) (5) (5) (5) (5)

Bz Bz Bz Cbz Fmoc Fmoc Fmoc

6 6 6 6+7 7 7 7

81 36 27 ∼30f ∼45f 41 ∼40f

80 (cis) 6 (cis) 20 (cis) na 73 80 na

>20:1 5:1 7:1

Reactions were conducted with 1.1 equiv of 4 and 1.0 equiv of 5a in the presence of catalyst 1a, 2a, or 3a in toluene at 40 °C. bIsolated yield. Determined by chiral HPLC. dDetermined by 1H NMR analysis. eAt 30 °C. fApproximate yields due to the production of an inseparable byproduct.

a c

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ACS Catalysis Table 3. Enantioselective [4 + 2] Cycloaddition of N-Benzoyl Imines with Alkenesa

Reactions were conducted with 1.1 equiv of 4a and 1.0 equiv of 5 in the presence of 5 mol % 1c in toluene at 0 °C. bIsolated yield. cDetermined by chiral HPLC. d2 equiv of 5e. e3 equiv of 5f.

a

(Table 1). We made two important observations regarding the factors that control these transformations. First, the product formation was heavily contingent upon the carbonyl substituent on the imine nitrogen. The treatment of N-benzoyl imine with the catalysts resulted in the formation of the cycloadduct 6 (entries 1−3). On the other hand, the reaction of N-Fmoc imine gave rise to the imino−ene product 7 exclusively (entries 5−7).18 In contrast to the sole production of either the cycloadduct 6 or the imino−ene product 7, when the imine nitrogen was replaced with a Cbz group, the reaction yielded a mixture of 6 and 7 (entry 4). Second, the impact of different perfluoroaryls depended on the type of reactions that occurred. In the [4 + 2] cycloaddition reaction, the use of 1a with a pentafluorophenyl group was essential to obtain high yields and high diastereo- and enantioselectivities (entries 1 vs 2 and 3). For the imino−ene reaction, significant differences were not observed when changing from 1a to 2a even at lower temperatures; whereas a minor improvement from ∼45% yield and 73% ee to 41% yield and 80% ee was detected (entries 5 vs 6). 2.2. Development of Enantioselective [4 + 2] Cycloaddition Reaction of N-Benzoyl Imines with Alkenes. On the basis of our initial studies, we turned our attention to developing the catalytic, asymmetric [4 + 2] cycloaddition reaction of N-benzoyl imines with alkenes to yield polysubstitued 5,6-dihydro-4H-1,3-oxazines in a diastereo- and enantioselective fashion (Table 2). 5,6-Dihydro-4H-1,3-oxazines, 6, are known to be key intermediates for the stereoselective synthesis of amine and amido derivatives; however, the only report of reactions of the N-acyliminium ion with alkenes indicated that

Scheme 1. Stereoselective Elaboration of Polysubstituted 5,6-Dihydro-4H-1,3-oxazine Derivatives

2. RESULTS AND DISCUSSION 2.1. Initial Study of Fluorinated Aryl-Incorporated Mono-Phosphoric Acids: Enantioselective Reactions of N-Acyl or N-Acyloxy Imine with α-Methylstyrene. We initially explored the reaction of the N-acyl or N-acyloxy imine 4 with α-methylstyrene (5a) in the presence of 1a or 2a 1200

DOI: 10.1021/acscatal.5b02136 ACS Catal. 2016, 6, 1198−1204

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aldehydes and a 9-fluorenylmethyl carbamate (FmocNH2).10a Thus, we exploited the enantioselective imino−ene reaction in a three-component manner. The development of the enantioselective three-component imino−ene reaction complements the substrate generality of the previous method. Furthermore, it extends the realm of chiral Brønsted acid catalyzed reactions for homoallylic amine synthesis beyond that of allylation reactions using allyl metal reagents.24,25 The development of the enantioselective three-component imino−ene reaction led us to evaluate the capabilities of fluorinated chiral monophosphoric acids in terms of yield and enantioselectivity (Table 4). Catalyst 1a facilitated the reaction

these were not enantioselective, and no successful examples for the catalytic asymmetric version of this reaction have been reported.15,19 We began our investigation by evaluating the effect of fluorinated aryl substituents at the 3,3′-position of 1. In order to assess the necessity of the perfluorinated phenyl group, the reaction was examined in the presence of a 3,4,5-trifluorophenyl-incorporated monophosphoric acid, 1b. It was found that 1b neither afforded a high yield nor stereoselectivity; in particular, the diastereo- and enantioselectivities dropped significantly in comparison to those obtained with 1a and 1c (entries 1 and 3 vs 2). This result, including the result by 3a, suggests that the perfluorination of the aryl substituents is important not only to realize an adequate catalytic activity but also to construct a sophisticated chiral environment.20 Encouraged by the 1a catalyzed [4 + 2] cycloaddition reaction, we used the modification of the benzoyl group on the imine to improve the enantioselectivity of the reaction. This study showed that 3,5-difluorobenzoyl group is an attractive substituent that led to promising enantioselectivities (entries 5−7). Finally, the reaction carried out at 0 °C in the presence of 5 mol % of 1c proceeded efficiently to yield cis adduct 6 in high yield with excellent enantioselectivity (entry 8). Having optimized the reaction conditions for the synthesis of 6-cis, we investigated the scope of 1c-catalyzed diastereo- and enantioselective [4 + 2] cycloaddition reactions of imines 4 with a variety of alkenes 5. These reactions proceeded well with a wide variety of imine carbon substituents and alkenes (Table 3). Not only with imines 4a−g, but, also, reactions with a heterocyclic imine such as 2-thienyl imine, 4h, proceeded smoothly to furnish the cycloadducts 6 with high diastereo- and enantiofacial control (entries 1−8). Moreover, the scope of the reaction was successfully extended to other alkenes under similar conditions; for example, 1c enabled the formation of cycloadducts 6 with excellent diastereo- and enantioselectivities in all cases (entries 9−11). Reactions of imine 4a with alkenes 5e or 5f produced the desired cycloadducts in low yields under the standard conditions; however, the yields could be improved by the use of 2 or 3 equiv of 5 (entries 12 and 13). The 1a- and 1c-catalyzed [4 + 2] cycloaddition reactions constitute the first examples of the diastereo- and enantioselective reactions of N-acyl imines and styrene compounds. The diastereo- and enantioselectivity of the process is vital for further synthetic applications of the polysubstituted 5,6-dihydro-4H-1,3-oxazine derivatives (Scheme 1). For instance, the ring opening of optically pure 6aa by hydrogenation, followed by the deprotection of 3,5-difluorobenzoyl group, yielded (1R,3S)-1,3-diphenylbutan-1-amine without any significant loss of enantioselectivity.21,22 The reduction of methylated 6aa, followed by the ring opening by the treatment of trifluoroacetic acid, afforded the 1,3-amino alcohol. Furthermore, no loss of stereochemical integrity was observed during the transformation of 6aa into the amino alcohol.23 2.3. Development of Enantioselective Imino−Ene Reaction of N-Fmoc Imines with Alkenes. In the context of the imino−ene reaction, an N-tosyl-α-iminoester has been used as the chelating and highly electrophilic component in all previous reports of chiral Lewis acid catalysis.14a−e Our initial study suggested that the imino−ene reaction proceeds when the benzaldehyde-derived N-Fmoc imine 4 was used as an electrophile (Table 1, entries 5 and 6).5 We expected that relatively stronger chiral Brønsted acids, such as 1a, 1c, and 2a, might generate N-Fmoc aldimines directly from the condensation of the

Table 4. Optimization of the Three-Component Imino−Ene Reactiona

entry d

1 2d 3d 4 5 6

catalyst

(mol %)

5

yield (%)b

ee (%)c

1a 1c 2a 2a 2b 3a

(5) (5) (5) (2.5) (2.5) (2.5)

5a 5a 5a 5d 5d 5d

46 ∼8e 99 97 55 7

65 56 83 82 69 58

a Reactions were conducted with 1.0 equiv of 8a, 1.05 equiv of FmocNH2, 5.0 equiv of 5a, or 3.0 equiv of 5d, and MS5Å in the presence of catalyst in toluene at 40 °C for 24 h. bIsolated yield. c Determined by chiral HPLC. d48 h. eApproximate yield due to the production of an inseparable byproduct.

of benzaldehyde (8a), FmocNH2, and α-methylstyrene (5a) to give an imino−ene product 7aa in moderate yield with moderate enantioselectivity (entry 1). Catalyst 1c, which was the best catalyst in [4 + 2] cycloaddition reaction, unable to give 7aa due to low solubility in toluene (entry 2). The same reaction, when conducted in the presence of 2a, proceeded smoothly to provide 7aa in quantitative yield with high enantioselectivity (entry 3). These experiments clearly indicate that 2a, with its F10binaphthyl skeleton, is more proficient at this reaction than 1a and 1c, which has a 3,3′-perfluoroarylincorporated binaphthyl, concerning catalytic activity and chiral efficiency (entries 1 and 2 vs 3). Further, we sought to determine the capability of 2a in catalyzing the imino−ene reaction of an alkene, α-methylentetralin (5d), because 5d has not been used as a nucleophilic component in the imino−ene reaction. When 2a was employed in the catalytic asymmetric 1201

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Table 5. Enantioselective Three-Component Imino−Ene Reaction of Aldehydes, 9-Fluorenylmethyl Carbamate, and Alkenesa

a Reactions were conducted with 1.0 equiv of 8, 1.05 equiv of FmocNH2, and 3.0 equiv of 5 in the presence of 2.5 mol % 2a in toluene at 40 °C for 24 h. bIsolated yield. cDetermined by chiral HPLC. dReaction was conducted with 1.0 equiv of 8a, 1.05 equiv of FmocNH2, and 5.0 equiv of 5 in the presence of 5.0 mol % 2a for 48 h. eReaction was conducted with 1.0 equiv of 8a, 1.05 equiv of FmocNH2, and 10 equiv of 5j in the presence of 10 mol % 2a for 72 h.

its analogs (5b, 5g, 5h) gave the desired imino−ene products in excellent yields with high enantioselectivites (entries 9−12). Moreover, methylenecyclohexane (5i) and 7-methoxy-1-methylidene-1,2,3,4-tetrahydronaphthalene (5j) were used successfully (entries 13−14).

three-component imino−ene reaction of 8a, FmocNH2, and 5d, it afforded product 7ad in excellent yield with high enantioselectivity (entry 4).14a,b,d To assess the importance of the F10binaphthyl framework, we conducted the reaction in the presence of 2b, assembled with the 3,3′-diphenyl F8binaphthyl,26 and 3a, assembled with the 3,3′-diphenyl binaphthyl. In both cases, a considerable decline in both the yields and the enantioselectivities was observed; from 97% yield and 82% ee to 55% yield and 69% ee and 7% yield and 58% ee, for 2b (entries 4 vs 5) and 3a (entry 6), respectively. These results clearly indicate that the F10binaphthyl skeleton is a valuable catalyst framework and that the fluorine at the 4,4′-position contributes to the excellent yields and high enantioselectivities observed. After optimizing catalyst 2a for the highly enantioselective three-component imino−ene reaction, we tested its performance for substrate generality (Table 5). Reactions of both aromatic and aliphatic aldehydes were carried out with 2a, affording high yields and enantioselectivities (entries 1−8). Notably, heterocyclic aldehydes such as 2-furancarboxaldehyde (8f), an alkenyl aldehyde such as 2-methylcinnamaldehyde (8g), and an aliphatic aldehyde such as cyclohexanecarboxaldehyde (8h) were well suited to this reaction; however, their N-acyloxy imines are difficult to synthesize and purify (entries 6−8).27 Also, the reaction of 8a with α-methylstyrene (5a) and

3. CONCLUSIONS The vast number of recent reports of reactions catalyzed by chiral phosphoric acids and their analogs fall into the category of highly reactive alkenes that possess a hydrogen bond donor site. These alkenes interact with the phosphoryl oxygen (PO) of the chiral phosphoric acids assisting in the progress of the reaction. In this report, we have shown that chiral monophosphoric acids incorporating perfluoaryls can be used as chiral Brønsted acid catalysts and deliver high yields and stereoselectivities in reactions with alkenes that do not have a hydrogen bond donor site. We have described the first examples of diastereo- and enantioselective [4 + 2] cycloaddition reactions of N-benzoyl imines, as well as enantioselective three-component imino−ene reactions using aldehydes and FmocNH2. Furthermore, we have also discussed the impact of the electronic and steric properties of the fluorine in the design of chiral monophosphoric acid catalysts. In particular, the F10binaphthyl skeleton is essential for asymmetric induction 1202

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C.; Dudding, T.; Drury, W. J.; Ryzhkov, L.; Taggi, A. E.; Lectka, T. J. Am. Chem. Soc. 2002, 124, 67−77. (9) For representative review of chiral phosphoric acid, see: (a) Terada, M. Synthesis 2010, 2, 1929−1982. (b) Akiyama, T. In Asymmetric Synthesis II; Christmann, M., Brase, S., Eds.; Wiley-VCH: Weinheim, 2012; pp 261−266. (c) Parmar, D.; Sugiono, E.; Raja, S.; Rueping, M. Chem. Rev. 2014, 114, 9047−9153. (10) For representative examples of chiral disulfonimide, see: (a) List, B.; Gandhi, S. Angew. Chem., Int. Ed. 2013, 52, 2573−2576. (b) Gemmeren, M.; Lay, F.; List, B. Aldrichimica Acta 2014, 47, 3−13. (11) For representative examples of N-triflyl phosphoramide, see: (a) Nakashima, D.; Yamamoto, H. J. Am. Chem. Soc. 2006, 128, 9626− 9627. (b) Jiao, P.; Nakashima, D.; Yamamoto, H. Angew. Chem., Int. Ed. 2008, 47, 2411−2413. (c) Rueping, M.; Nachtsheim, B. J.; Ieawsuwan, W.; Atodiresei, I. Angew. Chem., Int. Ed. 2011, 50, 6706− 6720. (d) Hashimoto, T.; Nakatsu, H.; Yamamoto, K.; Maruoka, K. J. Am. Chem. Soc. 2011, 133, 9730−9733. (e) Han, Z. Y.; Chen, D. F.; Wang, Y. Y.; Guo, R.; Wang, P. S.; Wang, C.; Gong, L. Z. J. Am. Chem. Soc. 2012, 134, 6532−6535. (12) For representative examples of 1,1′-binaphthyl-2,2′-disulfonic acid (BINSA), see: (a) Hatano, M.; Maki, T.; Moriyama, K.; Arinobe, M.; Ishihara, K. J. Am. Chem. Soc. 2008, 130, 16858−16860. (b) Hatano, M.; Sugiura, Y.; Ishihara, K. Tetrahedron: Asymmetry 2010, 21, 1311−1314. (c) Hatano, M.; Sugiura, Y.; Akakura, M.; Ishihara, K. Synlett 2011, 2011, 1247−1250. (d) Hatano, M.; Ozaki, T.; Sugiura, Y.; Ishihara, K. Chem. Commun. 2012, 48, 4986−4988. (e) Hatano, M.; Ishihara, K. Asian J. Org. Chem. 2014, 3, 352−365. (13) For representative examples of 1,1′-binaphthol-based imidodiphosphoric acid, see: (a) Coric, I.; List, B. Nature 2012, 483, 315−319. (b) Liao, S.; Coric, I.; Wang, Q.; List, B. J. Am. Chem. Soc. 2012, 134, 10765−10768. (c) Kim, J. H.; Coric, I.; Vellalath, S.; List, B. Angew. Chem., Int. Ed. 2013, 52, 4474−4477. (14) (a) Meer, F. T.; Feringa, B. L. Tetrahedron Lett. 1992, 33, 6695− 6696. (b) Drury, W. J.; Ferraris, D.; Cox, C.; Young, B.; Lectka, T. J. Am. Chem. Soc. 1998, 120, 11006−11007. (c) Yao, S.; Fang, X.; Jørgensen, A. K. Chem. Commun. 1998, 2547−2548. (d) Ferraris, D.; Young, B. C.; Dudding, T.; Drury, W. J.; Ryzhkov, L.; Taggi, A. E.; Lectka, T.; Cox, C. J. Am. Chem. Soc. 2002, 124, 67−77. (e) Caplan, N.; Hancock, F. E.; Bulman Page, P. C.; Hutchings, G. J. Angew. Chem., Int. Ed. 2004, 43, 1685−1688. (f) Oliver, L. H.; Puls, L. A.; Tobey, S. L. Tetrahedron Lett. 2008, 49, 4636−4639. (15) (a) Katritzky, A. R.; Ghiviriga, I.; Chen, K.; Tymoshenko, D. O.; Abdel-Fattah, A. A. A. J. Chem. Soc., Perkin Trans. 2 2001, 530−537. (b) Uddin, N.; Ulicki, J. S.; Foersterling, F. H.; Hossain, M. M. Tetrahedron Lett. 2011, 52, 4353−4356. (16) For seminal studies, see: (a) Akiyama, T.; Itoh, J.; Yokota, K.; Fuchibe, K. Angew. Chem., Int. Ed. 2004, 43, 1566−1568. (b) Uraguchi, D.; Terada, M. J. Am. Chem. Soc. 2004, 126, 5356−5357. (c) Terada, M.; Kanomata, K. Synlett 2011, 2011, 1255−1258. (17) (a) For highly enantioselective organocatalytic carbonyl−ene reaction, see: Rueping, M.; Theissmann, T.; Kuenkel, A.; Koenigs, R. M. Angew. Chem., Int. Ed. 2008, 47, 6798−6801. (b) For chiral Brønsted acid catalyzed cycloaddition of ortho-quinone methides with alkenes, see: Hsiao, C. C.; Raja, S.; Liao, H. H.; Atodiresei, I. A.; Rueping, M. Angew. Chem., Int. Ed. 2015, 54, 5762−5765. (18) The switch in reaction pathway may be due to the differences of the catalyst coordination to either the s-cis conformation of the Nbenzoyl imine or the s-trans conformation of the N-Fmoc imine. (19) Gizecki, P.; Dhal, R.; Poulard, C.; Gosselin, P.; Dujardin, G. J. Org. Chem. 2003, 68, 4338−4344. (20) The significant decline of enantioselectivity by 1b arises from the replacement of the fluorine atom (F) with the hydrogen atom (H). We speculate three possibilities: (i) the dihedral angle of phenyl− naphthyl axis of 1a may be different with that of 1b, due to the different types of interactions, i.e. noncovalent bond interaction F··· OP of 1a versus hydrogen bonding interaction H···OP of 1b, (ii) the steric effect of fluorine atom may significantly affect enantioselectivities, although there have been no significant differences of the size between hydrogen atom (H) and fluorine atom (F), and (iii) the

in the imino−ene reaction. Further studies regarding the perfluoroaryl based chiral molecular catalysts are ongoing in our group and will be reported in due course.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acscatal.5b02136. Experimental details, characterization data, HPLC enantiomer analysis, NMR spectra for new compounds, X-ray diffraction analysis (PDF) Crystal structure of the compound derived from 7aa (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (N.M.). *E-mail: [email protected] (M.T.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We sincerely thank Dr. Koji Yamamoto, Research Center of Integrative Molecular System, Institute for Molecular Science for the X-ray crystallographic analysis. Support was partially provided by JSPS via Grant-in-Aid for Young Scientist B (No. 21750087). We sincerely thank Central Glass Co., Ltd., for providing us octafluoronaphthalene.

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REFERENCES

(1) For representative reviews and reports, see: (a) Ishihara, K.; Yamamoto, H. Eur. J. Org. Chem. 1999, 1999, 527−538. (b) Hasegawa, A.; Ishihara, K.; Yamamoto, H. Angew. Chem., Int. Ed. 2003, 42, 5731− 5733. (c) Piers, W. E. Adv. Organomet. Chem. 2004, 52, 1−76. (d) Payette, J. N.; Yamamoto, H. J. Am. Chem. Soc. 2007, 129, 9536− 9537. (e) Hatano, M.; Mizuno, T.; Izumiseki, A.; Usami, R.; Asai, T.; Akakura, M.; Ishihara, K. Angew. Chem., Int. Ed. 2011, 50, 12189− 12192. (2) (a) Organofluorine Chemistry; Uneyama, K., Ed.; Wiley-Blackwell: Oxford, 2006. (b) Modern Fluoroorganic Chemistry: Synthesis, Reactivity, Applications; Kirsch, P., Ed.; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 2013. (3) (a) Akiyama, T.; Itoh, J.; Fuchibe, K. Adv. Synth. Catal. 2006, 348, 999−1010. (b) Kampen, D.; Reisinger, C. M.; List, B. Top. Curr. Chem. 2009, 291, 395−456. (c) Peng, F. Z.; Shao, Z. H. Curr. Org. Chem. 2011, 15, 4144−4160. (d) Trkmen, Y. E.; Zhu, Y.; Rawal, V. H. In Comprehensive Enantioselective Organocatalysis; Dalko, P. I., Ed.; Wiley: Weinheim, 2013; Vol. 8, pp 241−288. (e) Mase, N.; Hayashi, Y. In Comprehensive Organic Synthesis, 2nd ed.; Knochel, P., Molander, G. A., Eds.; Elsevier: Oxford, 2014; Vol. 1, pp 751−769. (4) Momiyama, N.; Nishimoto, H.; Terada, M. Org. Lett. 2011, 13, 2126−2129. (5) Momiyama, N.; Okamoto, H.; Shimizu, M.; Terada, M. Chirality 2015, 27, 464−475. (6) (a) Christ, P.; Lindsay, A. G.; Vormittag, S. S.; Neudorfl, J. M.; Berkessel, A.; O’Donoghue, A. M. C. Chem. - Eur. J. 2011, 17, 8524− 8528. (b) Yang, C.; Xue, X. S.; Jin, J. L.; Cheng, J. P.; Li, X. J. Org. Chem. 2013, 78, 7076−7085. (7) Mayr, H.; Kempf, B.; Ofial, A. R. Acc. Chem. Res. 2003, 36, 66− 77. (8) For representative example of enantioselective reaction of imines with allyltrimethylsilane, see: (a) Nakamura, K.; Nakamura, H.; Yamamoto, Y. J. Org. Chem. 1999, 64, 2614−2615. (b) Fang, X.; Johannsen, M.; Yao, S.; Gathergood, N.; Hazell, R. G.; Jørgensen, K. A. J. Org. Chem. 1999, 64, 4844−4849. (c) Ferraris, D.; Young, B.; Cox, 1203

DOI: 10.1021/acscatal.5b02136 ACS Catal. 2016, 6, 1198−1204

Research Article

ACS Catalysis stronger hydrogen bond may more stabilize transition state in 1a catalyzed reaction than that in 1b catalyzed reaction. (21) (a) Kim, J. Y.; Mu, Y.; Jin, X.; Park, S. H.; Pham, V. T.; Song, D. K.; Lee, K. Y.; Ham, W. H. Tetrahedron 2011, 67, 9426−9432. (b) Jin, T.; Kim, J. S.; Mu, Y.; Park, S. H.; Jin, X.; Kang, J. C.; Oh, C. Y.; Ham, W. H. Tetrahedron 2014, 70, 2570−2575. (c) Szostak, M.; Spain, M.; Eberhart, A. J.; Procter, D. J. J. Am. Chem. Soc. 2014, 136, 2268−2271. (22) A slight loss of enantioselectivity was observed under hydrogenation. (23) Li, P.; Evans, C. D.; Wu, Y.; Cao, B.; Hamel, E.; Joullie, M. M. J. Am. Chem. Soc. 2008, 130, 2351−2364. (24) For representative reviews, see: (a) Yamamoto, Y.; Asao, N. Chem. Rev. 1993, 93, 2207−2293. (b) Masse, C. E.; Panek, J. S. Chem. Rev. 1995, 95, 1293−1316. (c) Bloch, R. Chem. Rev. 1998, 98, 1407− 1438. (d) Kennedy, J. W. J.; Hall, D. G. Angew. Chem., Int. Ed. 2003, 42, 4732−4739. (e) Ding, H.; Friestad, G. K. Synthesis 2005, 2005, 2815−2829. (f) Friestad, G. K.; Mathies, A. K. Tetrahedron 2007, 63, 2541−2569. (g) Yamamoto, H.; Wadamoto, M. Chem. - Asian J. 2007, 2, 692−698. (h) Kanai, M.; Wada, R.; Shibuguchi, T.; Shibasaki, M. Pure Appl. Chem. 2008, 80, 1055−1062. (i) Kobayashi, S.; Mori, Y.; Fossey, J. S.; Salter, M. M. Chem. Rev. 2011, 111, 2626−2704. (j) Yus, M.; González-Gómez, J. C.; Foubelo, F. Chem. Rev. 2011, 111, 7774− 7854. (k) Yus, M.; González-Gómez, J. C.; Foubelo, F. Chem. Rev. 2013, 113, 5595−5698. (25) Lou, S.; Moquist, P. N.; Schaus, S. E. J. Am. Chem. Soc. 2007, 129, 15398−15404. (26) (a) Yudin, A. K.; Martyn, L. J. P.; Pandiaraju, S.; Zheng, J.; Lough, A. Org. Lett. 2000, 2, 41−44. (b) Yekta, S.; Krasnova, L. B.; Mariampillai, B.; Picard, C. J.; Chen, G.; Pandiaraju, S.; Yudin, A. K. J. Fluorine Chem. 2004, 125, 517−525. (c) Suzuki, S.; Furuno, H.; Inanaga, J.; Yokoyama, Y. Tetrahedron: Asymmetry 2006, 17, 504−507. (e) Rasmusson, T.; Martyn, L. J. P.; Chen, G.; Lough, A.; Oh, M.; Yudin, A. K. Angew. Chem., Int. Ed. 2008, 47, 7009−7012. (27) (a) Kanazawa, A. M.; Denis, J.; Greene, A. E. J. Org. Chem. 1994, 59, 1238−1240. (b) Kupfer, R.; Meier, S.; Würthwein, E. U. Synthesis 1984, 1984, 688−690. (c) Vidal, V.; Guy, L.; Sterin, S.; Collet, A. J. Org. Chem. 1993, 58, 4791−4793. (d) Gololobov, Y. G.; Kasukhin, L. F. Tetrahedron 1992, 48, 1353−1406.

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DOI: 10.1021/acscatal.5b02136 ACS Catal. 2016, 6, 1198−1204