A Convenient Preparation Method for Benzophenone Imine Catalyzed

Communication Cite This: Org. Process Res. Dev. XXXX, XXX, XXX−XXX

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A Convenient Preparation Method for Benzophenone Imine Catalyzed by Tetrabutylammonium Fluoride Yuta Kondo, Kazuhiro Morisaki,† Yoshinobu Hirazawa, Hiroyuki Morimoto,* and Takashi Ohshima* Graduate School of Pharmaceutical Sciences, Kyushu University, Maidashi 3-1-1, Higashi-ku, Fukuoka 812-8582, Japan

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S Supporting Information *

Scheme 1. Approaches for Synthesizing Benzophenone Imine

ABSTRACT: Benzophenone imine is a useful ammonia equivalent in the Buchwald−Hartwig amination and an important intermediate for the synthesis of N-protected primary amines. However, the conventional synthesis of benzophenone imine requires stoichiometric amounts of metal reagents or high-pressure conditions. Herein we report a facile method for preparing benzophenone imine to enhance its potential utility. The reaction is performed by mixing commercially available benzophenone and bis(trimethylsilyl)amine in the presence of a catalytic amount of tetrabutylammonium fluoride at ambient temperature and pressure and can be readily applied to a multigram-scale synthesis even in a standard academic laboratory setup. Preliminary mechanistic studies and the application of the reaction to one-pot benzophenone imine synthesis/Buchwald−Hartwig amination are also reported. KEYWORDS: tetrabutylammonium fluoride, benzophenone imine, Buchwald−Hartwig amination, one-pot synthesis

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INTRODUCTION Benzophenone imine, one of the most frequently used Nunsubstituted ketimines, is a well-established ammonia equivalent in Buchwald−Hartwig amination reactions.1−3 It is also an important synthetic intermediate, especially for the synthesis of glycine Schiff base, one of the most well-known starting materials for the synthesis of non-natural amino acid derivatives4 and related N-substituted ketimine derivatives.5 Benzophenone imine was also recently applied as a substrate for catalytic C−H functionalization reactions.6 Therefore, an efficient method for preparing benzophenone imine is important for the synthesis of nitrogen-containing compounds. Conventional preparation methods for benzophenone imine, however, have several drawbacks that limit their potential utility. For example, the addition of phenylmagnesium halides to benzonitrile, one of the most practical methods for preparing benzophenone imine, requires the use of air- and moisture-sensitive Grignard reagents and generates stoichiometric amounts of metal waste (Scheme 1, eq a). 7 Benzophenone imine is also accessible from benzophenone and excess ammonia, but this reaction requires the use of stoichiometric amounts of titanium chloride or a high-pressure apparatus (Scheme 1, eqs b and c).8 Although the recent development of synthetic methodologies allows for the synthesis of benzophenone imine in a catalytic manner © XXXX American Chemical Society

(Scheme 1, eqs d and e),9 the azide starting material is not readily applicable for large-scale synthesis, and benzhydrylamine is generally obtained by reductive amination of the parent benzophenone. Therefore, a much simpler and more convenient method for synthesizing benzophenone imine is highly desirable. To overcome these limitations, and in accordance with our recent interest in the chemistry of N-unsubstituted ketimines,10 we were interested in the transformation of benzophenone to benzophenone imine using bis(trimethylsilyl)amine as a nitrogen source and tetrabutylammonium fluoride (TBAF) as Special Issue: Honoring 25 Years of the Buchwald-Hartwig Amination Received: May 15, 2019

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DOI: 10.1021/acs.oprd.9b00226 Org. Process Res. Dev. XXXX, XXX, XXX−XXX

Organic Process Research & Development

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fluoride anion is important, several other tetrabutylammonium salts were examined, but none afforded 3 (entries 10−13). Finally, extending the reaction time of TBAF to 6 h afforded 3 in 97% isolated yield (entry 14). We next applied the optimized reaction conditions to a large-scale synthesis of 3. The reaction proceeded on a 10 mmol scale, and the crude mixture was purified by silica gel column chromatography to give 3 in 97% yield (Scheme 2, eq a). Furthermore, the reaction proceeded smoothly on a 60 mmol scale in a 100 mL flask to give 10 g of 3 after extraction and distillation (Scheme 2, eq b).

a catalyst (Scheme 1, eq f). Although TBAF is a known catalyst for the synthesis of N-sulfenyl imines from carbonyl compounds and bis(trimethylsilyl)sulfenamides,11 the method has not been applied to the synthesis of other imines, including benzophenone imine. We envisaged that benzophenone imine could be prepared from benzophenone if the parent bis(trimethylsilyl)amine could function as the nitrogen source. Herein we report our efforts to realize the reaction. Benzophenone and bis(trimethylsilyl)amine react in the presence of a catalytic amount of commercially available TBAF in THF to give benzophenone imine in good yield at ambient temperature and pressure, and the reaction can be readily applied to multigram-scale synthesis even in a simple academic laboratory setup. Preliminary mechanistic studies of the reaction and its application to one-pot benzophenone imine synthesis/Buchwald−Hartwig amination are also reported.

Scheme 2. Large-Scale Syntheses of Benzophenone Imine

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RESULTS AND DISCUSSION We initially examined the catalyst to test whether bis(trimethylsilyl)amine (2) could be used as a nitrogen source to transform benzophenone (1) to benzophenone imine (3) (Table 1). First, we evaluated several metal fluorides to find a Table 1. Catalyst Screeninga

entry

catalyst

3 (%)b

1 (%)b

1 2 3 4 5 6 7 8 9 10 11 12 13 14e

NaF KF CsF AgF TBAFc TBAF·xH2O TMAF TBAT DAST TBACl TBAOAc TBAOHd TBAH2F3 TBAFc

n.d. n.d. n.d. n.d. 87 77 4 7 n.d. n.d. n.d. n.d. n.d. >99 (97f)

>99 >99 >99 >99 13 23 96 93 >99 >99 >99 >99 >99 n.d.

To clarify the reaction pathway, we obtained preliminary mechanistic information. 1H NMR analysis of the crude mixture revealed that hexamethyldisiloxane was generated in the reaction mixture (Scheme 3, eq a), suggesting that the trimethylsilyl group in 2 acts as an oxygen scavenger. The reaction also proceeded in the presence of catalytic amounts of tetrabutylammonium chloride and potassium trimethylsilanolate (Scheme 3, eq b), while the same reaction did not proceed in the absence of tetrabutylammonium chloride. These results suggested that tetrabutylammonium trimethylsilanolate12 is one of the active species in the catalytic cycle. In addition, the presence of small amounts of water in the TBAF solution is important to promote the reaction effectively, as the addition of desiccants retarded the reaction to some extent (Scheme 3, eq c). On the basis of both the above experimental information and earlier studies in the literature,11c,13 we propose a possible reaction mechanism (Scheme 4). First, TBAF reacts with 2 in the presence of water to give tetrabutylammonium trimethylsilanolate I, which adds to 2 to give hexamethyldisiloxane and nucleophilic bis(trimethylsilyl)amide II. Next, the addition of II to 1 gives intermediate III, for which intramolecular migration of the trimethylsilyl group from the nitrogen atom to the oxygen atom gives intermediate IV. Finally, elimination of trimethylsilanolate from IV produces 3 and the starting tetrabutylammonium trimethylsilanolate I, closing the catalytic cycle. Finally, we applied our synthetic method for benzophenone imine to a one-pot Buchwald−Hartwig amination (Scheme 5).2b The expected cross-coupling reactions proceeded in a one-pot manner without isolation of 3, and the desired crosscoupling products 4a and 4b were obtained in high yields. These results demonstrated the potential applicability of our

a

The reactions were performed using 1 (1.0 mmol), 2 (2.0 equiv), and catalyst (10 mol %) in THF (0.10 mL) at room temperature for 2 h. Abbreviations: n.d. = not detected; TMAF = tetramethylammonium fluoride; TBAT = tetrabutylammonium difluorotriphenylsilicate; DAST = diethylaminosulfur trifluoride. bDetermined by 1H NMR analysis of the crude mixtures. cCommercially available TBAF solution (1.0 M in THF including 99% purity based on 1H NMR analysis). Preliminary Mechanistic Information 1: Intermediacy of Tetrabutylammonium Trimethylsilanolate (Scheme 3, Eq b). A 4 mL vial with a Teflon-lined screw cap equipped with a magnetic stir bar was dried under vacuum using a heat gun and refilled with argon. To the vial were added 1 (182 mg, 1.0 mmol), tetrabutylammonium chloride (27.8 mg, 0.10 mmol, 10 mol %), potassium trimethylsilanolate (12.8 mg, 0.10 mmol, 10 mol %), and THF (0.10 mL). The mixture was stirred at room temperature for 30 min before addition of 2 (0.42 mL, 2.0 mmol, 2.0 equiv). The resulting mixture was further stirred at room temperature (25 °C) for 2 h, and the yield of 3 was determined by 1H NMR analysis of the crude mixture. The above reaction was also performed in the absence of tetrabutylammonium chloride, and the product 3 was not detected by 1H NMR analysis of the crude mixture. Preliminary Mechanistic Information 2: Addition of Desiccants (Scheme 3, Eq c). A 4 mL vial with a Teflonlined screw cap equipped with a magnetic stir bar was charged with desiccant (100 mg/mmol), and the vial was dried under vacuum using a heat gun and refilled with argon. To the vial were added 1 (182 mg, 1.0 mmol), 2 (0.42 mL, 2.0 mmol, 2.0 equiv), and tetrabutylammonium fluoride (1.0 M in tetrahydrofuran) (0.10 mL, 0.10 mmol, 10 mol %). The vial was stirred at room temperature (25 °C) for 6 h, and the yield of 3 was determined by 1H NMR analysis of the crude mixture. General Procedure for One-Pot Catalytic Benzophenone Imine Synthesis and Buchwald−Hartwig Amination (Scheme 5). A 20 mL Schlenk tube equipped with a magnetic stir bar was dried under vacuum using a heat gun and refilled with argon. To the flask were added 1 (182 mg, 1.0 mmol), 2 (0.42 mL, 2.0 mmol, 2.0 equiv), and tetrabutylammonium fluoride (1.0 M in tetrahydrofuran) (0.10 mL, 0.10 mmol, 10 mol %). The tube was stirred at room temperature (25 °C) for 6 h. After the consumption of 1 was confirmed by 1H NMR analysis, Pd(OAc)2 (2.25 mg, 0.010 mmol, 1.0 mol %), DPPF (8.32 mg, 0.015 mmol, 1.5 mol %), NaOtBu (115 mg, 1.2 mmol, 1.2 equiv), toluene (5.0 mL, 0.20 M), and aryl bromide (1.2 mmol, 1.2 equiv) were added to the reaction mixture under an argon atmosphere. The mixture was further stirred at 100 °C for 6 h. After the consumption of 3 was confirmed by 1H NMR analysis, the crude mixture was directly purified by flash silica gel column chromatography to give the cross-coupling product 4. N-(4-Methoxyphenyl)-1,1-diphenylmethanimine (4a)2f (Scheme 5). The reaction was performed according to the general procedure with 4-bromoanisole (160 μL, 1.2 mmol), and the crude mixture was directly purified by flash silica gel column chromatography using 20:1 to 10:1 hexane/EtOAc with 1% NEt3 as the eluent to give N-(4-methoxyphenyl)-1,1diphenylmethanimine (4a) as a yellow oil (268 mg, 93% yield). 1H NMR (500 MHz, CDCl3): δ 7.74−7.71 (m, 2H), 7.46−7.43 (m, 1H), 7.40−7.37 (m, 2H), 7.31−7.27 (m, 3H), 7.13−7.11 (m, 2H), 6.70−6.66 (m, 4H), 3.72 (s, 3H). 13C NMR (125 MHz, CDCl3): δ 167.77, 155.83, 144.33, 140.02,

CDCl3 at 77.0 ppm for 13C{1H}). Coupling constants are reported in hertz. The following abbreviations are used: s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, br = broad. Benzophenone (1) was purchased from FUJIFILM Wako Pure Chemical Corporation. 1,1,1,3,3,3-Hexamethyldisilazane (2) was purchased from Tokyo Chemical Industry Co., Ltd. and dried over 4 Å molecular sieves before use. TBAF solution (1.0 M in THF including 99% purity based on 1H NMR analysis). Procedure for 60 mmol Scale Synthesis (Scheme 2, Eq b). A 100 mL flask equipped with a magnetic stir bar was dried under vacuum using a heat gun and refilled with argon. To the flask were added 1 (10.9 g, 60 mmol), 2 (25.2 mL, 120 mmol, 2.0 equiv), and tetrabutylammonium fluoride (1.0 M in tetrahydrofuran) (6.0 mL, 6.0 mmol, 10 mol %). The flask was stirred at room temperature for 6 h. After the consumption of 1 was confirmed by 1H NMR analysis (>99% conversion based on 1H NMR analysis of the crude mixture), the crude mixture was quenched with H2O (100 mL) and extracted with Et2O (60 mL × 2). The combined organic layer was dried over Na2SO4, filtered in a 100 mL flask, and evaporated under D



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Catalyzed C−N Cross-Coupling Reactions. Chem. Rev. 2016, 116, 12564−12649. (2) For selected examples using benzophenone imine as an ammonia equivalent in Buchwald−Hartwig amination, see: (a) Wolfe, J. P.; Åhman, J.; Sadighi, J. P.; Singer, R. A.; Buchwald, S. L. An Ammonia Equivalent for the Palladium-Catalyzed Amination of Aryl Halides and Triflates. Tetrahedron Lett. 1997, 38, 6367−6370. (b) Mann, G.; Hartwig, J. F.; Driver, M. S.; Fernández-Rivas, C. Palladium-Catalyzed C−N(sp2) Bond Formation: N-Arylation of Aromatic and Unsaturated Nitrogen and the Reductive Elimination Chemistry of Palladium Azolyl and Methyleneamido Complexes. J. Am. Chem. Soc. 1998, 120, 827−828. (c) Grasa, G. A.; Viciu, M. S.; Huang, J.; Nolan, S. P. Amination Reactions of Aryl Halides with Nitrogen-Containing Reagents Mediated by Palladium/Imidazolium Salt Systems. J. Org. Chem. 2001, 66, 7729−7737. (d) Kampmann, S. S.; Skelton, B. W.; Wild, D. A.; Koutsantonis, G. A.; Stewart, S. G. An Air-Stable Nickel(0) Phosphite Precatalyst for Primary Alkylamine C−N CrossCoupling Reactions. Eur. J. Org. Chem. 2015, 2015, 5995−6004. (e) Peacock, D. M.; Roos, C. B.; Hartwig, J. F. Palladium-Catalyzed Cross Coupling of Secondary and Tertiary Alkyl Bromides with a Nitrogen Nucleophile. ACS Cent. Sci. 2016, 2, 647−652. (f) Power, D. J.; Jones, K. D.; Kampmann, S. S.; Flematti, G. R.; Stewart, S. G. Nickel-Catalyzed C−N Cross-Coupling of Primary Imines with Subsequent In Situ [2 + 2] Cycloaddition or Alkylation. Asian J. Org. Chem. 2017, 6, 1794−1799. (3) For reviews of the use of other ammonia surrogates and ammonia itself in Buchwald−Hartwig amination reactions, see: (a) Aubin, Y.; Fischmeister, C.; Thomas, C. M.; Renaud, J.-L. Direct amination of aryl halides with ammonia. Chem. Soc. Rev. 2010, 39, 4130−4145. (b) Klinkenberg, J. L.; Hartwig, J. F. Catalytic Organometallic Reactions of Ammonia. Angew. Chem., Int. Ed. 2011, 50, 86−95. (c) Schranck, J.; Tlili, A. Transition-MetalCatalyzed Monoarylation of Ammonia. ACS Catal. 2018, 8, 405− 418. (d) Lavoie, C. M.; Stradiotto, M. Bisphosphines: A Prominent Ancillary Ligand Class for Application in Nickel-Catalyzed C−N Cross-Coupling. ACS Catal. 2018, 8, 7228−7250. For selected examples, see: (e) Jaime-Figueroa, S.; Liu, Y.; Muchowski, J. M.; Putman, D. G. Allyl amines as ammonia equivalents in the preparation of anilines and heteroarylamines. Tetrahedron Lett. 1998, 39, 1313− 1316. (f) Lee, S.; Jørgensen, M.; Hartwig, J. F. Palladium-Catalyzed Synthesis of Arylamines from Aryl Halides and Lithium Bis(trimethylsilyl)amide as an Ammonia Equivalent. Org. Lett. 2001, 3, 2729−2732. (g) Huang, X.; Buchwald, S. L. New Ammonia Equivalents for the Pd-Catalyzed Amination of Aryl Halides. Org. Lett. 2001, 3, 3417−3419. (h) Lee, D.-Y.; Hartwig, J. F. Zinc Trimethylsilylamide as a Mild Ammonia Equivalent and Base for the Amination of Aryl Halides and Triflates. Org. Lett. 2005, 7, 1169− 1172. (i) Shen, Q.; Hartwig, J. F. Palladium-Catalyzed Coupling of Ammonia and Lithium Amide with Aryl Halides. J. Am. Chem. Soc. 2006, 128, 10028−10029. (j) Surry, D. S.; Buchwald, S. L. Selective Palladium-Catalyzed Arylation of Ammonia: Synthesis of Anilines as Well as Symmetrical and Unsymmetrical Di- and Triarylamines. J. Am. Chem. Soc. 2007, 129, 10354−10355. (k) Schulz, T.; Torborg, C.; Enthaler, S.; Schäffner, B.; Dumrath, A.; Spannenberg, A.; Neumann, H.; Börner, A.; Beller, M. A General Palladium-Catalyzed Amination of Aryl Halides with Ammonia. Chem. - Eur. J. 2009, 15, 4528−4533. (l) Lundgren, R. J.; Peters, B. D.; Alsabeh, P. G.; Stradiotto, M. A P,N-Ligand for Palladium-Catalyzed Ammonia Arylation: Coupling of Deactivated Aryl Chlorides, Chemoselective Arylations, and Room Temperature Reactions. Angew. Chem., Int. Ed. 2010, 49, 4071−4074. (m) Isley, N. A.; Dobarco, S.; Lipshutz, B. H. Installation of protected ammonia equivalents onto aromatic & heteroaromatic rings in water enabled by micellar catalysis. Green Chem. 2014, 16, 1480−1488. (n) Green, R. A.; Hartwig, J. F. Palladium-Catalyzed Amination of Aryl Chlorides and Bromides with Ammonium Salts. Org. Lett. 2014, 16, 4388−4391. (o) Green, R. A.; Hartwig, J. F. Nickel-Catalyzed Amination of Aryl Chlorides with Ammonia or Ammonium Salts. Angew. Chem., Int. Ed. 2015, 54, 3768−3772. (p) Borzenko, A.; RottaLoria, N.; MacQueen, P. M.; Lavoie, C. M.; McDonald, R.; Stradiotto,

136.60, 130.48, 129.55, 129.17, 128.45, 128.13, 128.00, 122.56, 113.72, 55.28. 4-((Diphenylmethylene)amino)benzonitrile (4b) 2 f (Scheme 5). The reaction was performed according to the general procedure with 4-bromobenzonitrile (218 mg, 1.2 mmol), and the crude mixture was directly purified by flash silica gel column chromatography using 20:1 hexane/EtOAc with 1% NEt3 as the eluent to give 4-((diphenylmethylene)amino)benzonitrile (4b) as a pale-yellow solid (261 mg, 93% yield). 1H NMR (500 MHz, CDCl3): δ 7.75 (d, J = 7.5 Hz, 2H), 7.51 (t, J = 7.0 Hz, 1H), 7.43 (dt, J = 8.5, 2.0 Hz, 4H), 7.33−7.28 (m, 3H), 7.09 (d, J = 7.0 Hz, 2H), 6.77 (dt, J = 8.5, 2.0 Hz, 2H). 13C NMR (125 MHz, CDCl3): δ 169.44, 155.44, 138.53, 135.20, 132.71, 131.39, 129.50, 129.17, 129.17, 128.30, 128.13, 121.33, 119.25, 106.14.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.oprd.9b00226.

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NMR spectra of products and reaction mixtures (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Hiroyuki Morimoto: 0000-0003-4172-2598 Takashi Ohshima: 0000-0001-9817-6984 Present Address †

K.M.: Institute for Chemical Research, Kyoto University, Kyoto 611-0011, Japan. Notes

The authors declare the following competing financial interest(s): a part of the work in this article has been filed in a patent application.

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ACKNOWLEDGMENTS This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas (JSPS KAKENHI Grant JP15H05846 in Middle Molecular Strategy to T.O.) and Grants-in-Aid for Scientific Research (B) (JSPS KAKENHI Grant JP17H03972 to T.O.) and (C) (JSPS KAKENHI Grant JP18K06581 to H.M.) from JSPS and Basis for Supporting Innovative Drug Discovery and Life Science Research (BINDS) (Grant JP18am0101091) from AMED. Y.K. and K.M. thank JSPS for Research Fellowships for Young Scientists. Y.K. is grateful for the support from the Academic Challenge Program 2018 of Kyushu University.

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REFERENCES

(1) For general information, see: (a) Hartwig, J. F. Organotransition Metal Chemistry: From Bonding to Catalysis; University Science Books: Sausalito, CA, 2010. For selected reviews, see: (b) Surry, D. S.; Buchwald, S. L. Biaryl Phosphane Ligands in Palladium-Catalyzed Amination. Angew. Chem., Int. Ed. 2008, 47, 6338−6361. (c) Hartwig, J. F. Evolution of a Fourth Generation Catalyst for the Amination and Thioetherification of Aryl Halides. Acc. Chem. Res. 2008, 41, 1534− 1544. (d) Surry, D. S.; Buchwald, S. L. Dialkylbiaryl phosphines in Pd-catalyzed amination: a user’s guide. Chem. Sci. 2011, 2, 27−50. (e) Ruiz-Castillo, P.; Buchwald, S. L. Applications of PalladiumE



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M. Nickel-Catalyzed Monoarylation of Ammonia. Angew. Chem., Int. Ed. 2015, 54, 3773−3777. (q) Schranck, J.; Furer, P.; Hartmann, V.; Tlili, A. Nickel-Catalyzed Amination of Aryl Carbamates with Ammonia. Eur. J. Org. Chem. 2017, 2017, 3496−3500. (4) (a) O’Donnell, M. J.; Polt, R. L. A mild and efficient route to Schiff base derivatives of amino acids. J. Org. Chem. 1982, 47, 2663− 2666. (b) O’Donnell, M. J.; Bennett, W. D.; Wu, S. The stereoselective synthesis of α-amino acids by phase-transfer catalysis. J. Am. Chem. Soc. 1989, 111, 2353−2355. For selected recent reviews of the synthesis of amino acid derivatives using glycine Schiff base, see: (c) Shirakawa, S.; Maruoka, K. Recent Developments in Asymmetric Phase-Transfer Reactions. Angew. Chem., Int. Ed. 2013, 52, 4312−4348. (d) Tan, J.; Yasuda, N. Contemporary Asymmetric Phase Transfer Catalysis: Large-Scale Industrial Applications. Org. Process Res. Dev. 2015, 19, 1731−1746. O’Donnell, M. J. Benzophenone Schiff bases of glycine derivatives: Versatile starting materials for the synthesis of amino acids and their derivatives. Tetrahedron 2019, 75, 3667−3696. (5) For selected reviews, see: (a) O’Donnell, M. J. Benzophenone Imine. In Encyclopedia of Reagents for Organic Synthesis; John Wiley & Sons, 2001. (b) Tang, S.; Zhang, X.; Sun, J.; Niu, D.; Chruma, J. J. 2Azaallyl Anions, 2-Azaallyl Cations, 2-Azaallyl Radicals, and Azomethine Ylides. Chem. Rev. 2018, 118, 10393−10457. For selected recent examples, see: (c) Huang, H.; Chen, W.; Xu, Y.; Li, J. I−/TBHP catalyzed Csp3−N/Csp2−N bond formation via oxidative coupling with benzophenone imine in water. Green Chem. 2015, 17, 4715−4719. (d) Lim, J. J.; Leitch, D. C. Lewis Acid-Catalyzed Addition of Benzophenone Imine to Epoxides Enables the Selective Synthesis and Derivatization of Primary 1,2-Amino Alcohols. Org. Process Res. Dev. 2018, 22, 641−649. (e) Mao, R.; Balon, J.; Hu, X. Cross-Coupling of Alkyl Redox-Active Esters with Benzophenone Imines: Tandem Photoredox and Copper Catalysis. Angew. Chem., Int. Ed. 2018, 57, 9501−9504. (6) For selected examples of the use of benzophenone imine in C− H functionalization reactions, see: (a) Ueura, K.; Satoh, T.; Miura, M. Rhodium-Catalyzed Arylation Using Arylboron Compounds: Efficient Coupling with Aryl Halides and Unexpected Multiple Arylation of Benzonitrile. Org. Lett. 2005, 7, 2229−2231. (b) Fukutani, T.; Umeda, N.; Hirano, K.; Satoh, T.; Miura, M. Rhodium-catalyzed oxidative coupling of aromatic imines with internal alkynes via regioselective C−H bond cleavage. Chem. Commun. 2009, 5141− 5143. (c) Sun, Z.-M.; Chen, S.-P.; Zhao, P. Tertiary Carbinamine Synthesis by Rhodium-Catalyzed [3 + 2] Annulation of NUnsubstituted Aromatic Ketimines and Alkynes. Chem. - Eur. J. 2010, 16, 2619−2627. (d) Tran, D. N.; Cramer, N. syn-Selective Rhodium(I)-Catalyzed Allylations of Ketimines Proceeding through a Directed C−H Activation/Allene Addition Sequence. Angew. Chem., Int. Ed. 2010, 49, 8181−8184. (e) Tran, D. N.; Cramer, N. Enantioselective Rhodium(I)-Catalyzed [3 + 2] Annulations of Aromatic Ketimines Induced by Directed C−H Activations. Angew. Chem., Int. Ed. 2011, 50, 11098−11102. (f) He, R.; Huang, Z.-T.; Zheng, Q.-Y.; Wang, C. Manganese-Catalyzed Dehydrogenative [4 + 2] Annulation of N−H Imines and Alkynes by C−H/N−H Activation. Angew. Chem., Int. Ed. 2014, 53, 4950−4953. (g) Jia, T.; Zhao, C.; He, R.; Chen, H.; Wang, C. Iron-Carbonyl-Catalyzed Redox-Neutral [4 + 2] Annulation of N−H Imines and Internal Alkynes by C−H Bond Activation. Angew. Chem., Int. Ed. 2016, 55, 5268−5271. (h) Kim, J. H.; Greßies, S.; Glorius, F. Cooperative Lewis Acid/Cp*CoIII Catalyzed C−H Bond Activation for the Synthesis of Isoquinolin-3-ones. Angew. Chem., Int. Ed. 2016, 55, 5577−5581. (i) Xu, W.; Yoshikai, N. N−H Imine as a Powerful Directing Group for Cobalt-Catalyzed Olefin Hydroarylation. Angew. Chem., Int. Ed. 2016, 55, 12731−12735. (7) (a) Cornell, E. F. The Carbazylic Acids: The Ammonia Analogs of the Carboxylic Acids. J. Am. Chem. Soc. 1928, 50, 3311−3318. (b) Pickard, P. L.; Tolbert, T. L. An Improved Method of Ketimine Synthesis. J. Org. Chem. 1961, 26, 4886−4888. (c) Pickard, P. L.; Tolbert, T. L. Diphenyl Ketimine. Org. Synth. 1964, 44, 51−53.

(8) (a) Brenner, D. G.; Cavolowsky, K. M.; Shepard, K. L. Iminobridged heterocycles. IV. A facile synthesis of sulfenimines derived from diaryl ketones. J. Heterocycl. Chem. 1985, 22, 805−808. (b) Verardo, G.; Giumanini, A. G.; Strazzolini, P.; Poiana, M. Ketimines From Ketones and Ammonia. Synth. Commun. 1988, 18, 1501−1511. (9) (a) Lee, J. H.; Gupta, S.; Jeong, W.; Rhee, Y. H.; Park, J. Characterization and Utility of N-Unsubstituted Imines Synthesized from Alkyl Azides by Ruthenium Catalysis. Angew. Chem., Int. Ed. 2012, 51, 10851−10855. (b) Pramanik, S.; Reddy, R. R.; Ghorai, P. Transition Metal-Free Generation of N-Unsubstituted Imines from Benzyl Azides: Synthesis of N-Unsubstituted Homoallylic Amines. J. Org. Chem. 2015, 80, 3656−3663. (c) Damodara, D.; Arundhathi, R.; Likhar, P. R. Copper Nanoparticles from Copper Aluminum Hydrotalcite: An Efficient Catalyst for Acceptor- and Oxidant-Free Dehydrogenation of Amines and Alcohols. Adv. Synth. Catal. 2014, 356, 189−198. (10) For our recent contributions to the chemistry of Nunsubstituted ketimines, see: (a) Morisaki, K.; Morimoto, H.; Ohshima, T. Direct access to N-unprotected tetrasubstituted propargylamines via direct catalytic alkynylation of N-unprotected trifluoromethyl ketimines. Chem. Commun. 2017, 53, 6319−6322. (b) Sawa, M.; Morisaki, K.; Kondo, Y.; Morimoto, H.; Ohshima, T. Direct Access to N-Unprotected α- and/or β-Tetrasubstituted Amino Acid Esters via Direct Catalytic Mannich-Type Reactions Using NUnprotected Trifluoromethyl Ketimines. Chem. - Eur. J. 2017, 23, 17022−17028. (c) Yonesaki, R.; Kondo, Y.; Akkad, W.; Sawa, M.; Morisaki, K.; Morimoto, H.; Ohshima, T. 3-Mono-Substituted BINOL Phosphoric Acids as Effective Organocatalysts in Direct Enantioselective Friedel-Crafts-Type Alkylation of N-Unprotected αKetiminoester. Chem. - Eur. J. 2018, 24, 15211−15214. (d) Sawa, M.; Miyazaki, S.; Yonesaki, R.; Morimoto, H.; Ohshima, T. Catalytic Enantioselective Decarboxylative Mannich-Type Reaction of NUnprotected Isatin-Derived Ketimines. Org. Lett. 2018, 20, 5393− 5397. For selected recent contributions from other groups, see: (e) Jang, H.; Romiti, F.; Torker, S.; Hoveyda, A. H. Catalytic diastereo- and enantioselective additions of versatile allyl groups to N−H ketimines. Nat. Chem. 2017, 9, 1269−1275. (f) GallardoDonaire, J.; Hermsen, M.; Wysocki, J.; Ernst, M.; Rominger, F.; Trapp, O.; Hashmi, A. S. K.; Schäfer, A.; Comba, P.; Schaub, T. Direct Asymmetric Ruthenium-Catalyzed Reductive Amination of Alkyl−Aryl Ketones with Ammonia and Hydrogen. J. Am. Chem. Soc. 2018, 140, 355−361. (g) Rong, J.; Seeberger, P. H.; Gilmore, K. Chemoselective Photoredox Synthesis of Unprotected Primary Amines Using Ammonia. Org. Lett. 2018, 20, 4081−4085. (h) Miyagawa, M.; Yoshida, M.; Kiyota, Y.; Akiyama, T. Enantioselective Friedel−Crafts Alkylation Reaction of Heteroarenes with N-Unprotected Trifluoromethyl Ketimines by Means of Chiral Phosphoric Acid. Chem. - Eur. J. 2019, 25, 5677−5681. Also see ref 6. (11) (a) Morimoto, T.; Nezu, Y.; Achiwa, K.; Sekiya, M. A new synthetic method for sulphenimines. Fluoride-catalysed reaction of N,N-bis(trimethylsilyl)sulphenamides with aldehydes and ketones. J. Chem. Soc., Chem. Commun. 1985, 1584−1585. For related studies, see: (b) Morimoto, T.; Sekiya, M. A Convenient Synthetic Method for Schiff Bases. The trimethylsilyl trifluoromethanesulfonatecatalyzed reaction of N,N-bis(trimethylsilyl)amines with aldehydes and ketones. Chem. Lett. 1985, 14, 1371−1372. (c) Corriu, R. J. P.; Moreau, J. J. E.; Pataud-Sat, M. Silylamines in organic synthesis. Reactivity of N,N-bis(silyl)enamines toward electrophiles. A route to substituted 2-aza-1,3-butadienes and pyridines. J. Org. Chem. 1990, 55, 2878−2884. (d) Corriu, R. J. P.; Huynh, V.; Iqbal, J.; Moreau, J. J. E.; Vernhet, C. Silylamines in organic synthesis. Facile synthetic routes to unsaturated protected primary amines. Tetrahedron 1992, 48, 6231−6244. (12) For in situ generation of tetrabutylammonium trimethylsilanolate, see: (a) Di Bussolo, V.; Caselli, M.; Romano, M. R.; Pineschi, M.; Crotti, P. Stereospecific Uncatalyzed α-O-Glycosylation and α-CGlycosidation by Means of a New D-Gulal-Derived α-Vinyl Oxirane. J. Org. Chem. 2004, 69, 7383−7386. (b) Das, M.; O’Shea, D. F. Bu4N+ F



Communication

Alkoxide-Initiated/Autocatalytic Addition Reactions with Organotrimethylsilanes. J. Org. Chem. 2014, 79, 5595−5607. (13) Singh, R. P.; Cao, G.; Kirchmeier, R. L.; Shreeve, J. M. Cesium Fluoride Catalyzed Trifluoromethylation of Esters, Aldehydes, and Ketones with (Trifluoromethyl)trimethylsilane. J. Org. Chem. 1999, 64, 2873−2876. (14) We also examined 4,4′-dimethyl-, 4,4′-dimethoxy-, and 4,4′dichlorobenzophenone as substrates under the optimized reaction conditions, but the results were not optimal (39% yield, n.d., and 51% yield based on NMR analysis, respectively), and further screening of conditions is required. (15) Pintér, Á .; Haberhauer, G.; Hyla-Kryspin, I.; Grimme, S. Configurationally stable propeller-like triarylphosphine and triarylphosphine oxide. Chem. Commun. 2007, 3711−3713.

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A Convenient Preparation Method for Benzophenone Imine Catalyzed

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