Oxidative Coupling of N-Methoxyamides and Related Compounds toward Aromatic Hydrocarbons by Designer μ-Oxo Hypervalent Iodine Catalyst

Published as part of the 50 Years SYNTHESIS – Golden Anniversary Issue

Abstract

Oxidative coupling strategies that can directly convert the C–H group for chemical transformations are, in theory, ideal synthetic methods to reduce the number of synthetic steps and byproduct generation. Hypervalent iodine reagents have now become one of the most promising tools in developing oxidative couplings due to their unique reactivities that are replacing metal oxidants. As part of our continuous development of oxidative coupling reactions, we describe in this report highly efficient μ-oxo hypervalent iodine catalysts for the direct oxidative coupling of N-methoxyamides and related compounds with aromatic hydrocarbons. The excellent TONs, up to over 100 times, with a best catalyst loading of 0.5 mol% were determined for the oxidative C–H/N–H coupling method, which can provide the most straightforward route to obtaining these unique arylamide compounds.

Key words

hypervalent compound - iodine - oxidative coupling - amidation - electrophilic substitution

• References


For selected reviews, accounts, and publications, see:
• 1a Anastasia L, Negishi E. Handbook of Organopalladium Chemistry for Organic Synthesis . Wiley; New York: 2002: 311-334
• 1b Metal-Catalyzed Cross-Coupling Reactions . Diederich F, Stang PJ. Wiley-VCH; Weinheim: 2004
• 1c Negishi E. Angew. Chem. Int. Ed. 2011; 50: 6738, Nobel Lecture
• 1d Suzuki A. Angew. Chem. Int. Ed. 2011; 50: 6722; Nobel Lecture
• 1e Science of Synthesis: Cross Coupling and Heck-Type Reactions 1 . Molander GA. Wolfe JP. Larhed M. Thieme; Stuttgart: 2013

For reviews, see:
• 2a Yang BH, Buchwald SL. J. Organomet. Chem. 1999; 576: 125
• 2b Hartwig JF. Handbook of Organopalladium Chemistry for Organic Synthesis . Negishi E.-i. Wiley; New York: 2002: 1051
• 2c Janey JM. Name Reactions for Functional Group Transformations . Li JJ, Corey EJ. John Wiley & Sons; Hoboken: 2007: 564-609
• 2d Ruiz-Castillo P, Buchwald SL. Chem. Rev. 2016; 116: 12564
• 2e Heravi MM, Kheilkordi Z, Zadsirjan V, Heydari M, Malmir M. J. Organomet. Chem. 2018; 861: 17

For selected summarizations, see:
• 3a Torborg C, Beller M. Adv. Synth. Catal. 2009; 351: 3027
• 3b Biffis A, Centomo P, Del Zotto A, Zecca M. Chem. Rev. 2018; 118: 2249
• 3c Palladium-Catalyzed Coupling Reactions: Practical Aspects and Future Developments. Molnár A. Wiley–VCH; Weinheim: 2013
• 3d Cooper T, Campbell I, Macdonald S. Angew. Chem. Int. Ed. 2010; 49: 8082
• 3e Brown DG, Bostrom J. J. Med. Chem. 2016; 59: 4443
• 3f Cernak T, Dykstra KD, Tyagarajan S, Vachalb P, Krska SW. Chem. Soc. Rev. 2016; 45: 546
• 3g Devendar P, Qu R, Kang W.-M, He B, Yang G.-F. J. Agric. Food Chem. 2018; 66: 8914

Heck reaction is an early pioneer for the C–H coupling toward organic halides. See:
• 4a Heck RF. Org. React. 1982; 27: 345

For the trials reported in 2000s for other types of C–H coupling reactions, see:
• 4b Alberico D, Scott ME, Lautens M. Chem. Rev. 2007; 107: 174
• 4c Seregin IY, Gevorgyan V. Chem. Soc. Rev. 2007; 36: 1173
• 4d Chen X, Engle KM, Wang D.-H, Yu J.-Q. Angew. Chem. Int. Ed. 2009; 48: 5094
• 4e Lyons TW, Sanford MS. Chem. Rev. 2010; 110: 1147
• 4f Zhang Y.-F, Shi Z.-J. Acc. Chem. Res. 2019; 52: 161

For recent summaries, see:
• 5a From C–H to C–C Bonds: Cross-Dehydrogenative-Coupling . Li C.-J. RSC Green Chemistry Series; Cambridge: 2015
• 5b Tang S, Zeng L, Lei A. J. Am. Chem. Soc. 2018; 140: 13128
• 5c Yang Y, Lan J, You J. Chem. Rev. 2017; 117: 8787
• 5d Varun BV, Dhineshkumar J, Bettadapur KR, Siddaraju Y, Alagiri K, Prabhu KR. Tetrahedron Lett. 2017; 58: 803
• 5e He K.-H, Li Y. ChemSusChem 2014; 7: 2788

For early discussions, see:
• 6a Dhingra OP. Oxidation in Organic Chemistry . In Organic Chemistry, Part D, Vol. 5. Trahanovsky WS. Academic Press; New York: 1982: 207
• 6b Brunow G, Kilpeläinen I, Sipilä J, Syrjänen K, Karhunen P, Setälä H, Rummakko P. Lignin and Lignan Biosynthesis . Lewis NG, Sarkanen S. ACS Symposium Series 687; American Chemical Society; Washington: 1998: 131
• 6c Lessene G, Feldman KS. Modern Arene Chemistry . Astruc D. Wiley-VCH; Weinheim: 2002: 479-538

For recent interest of metal-free couplings and the use of hypervalent iodine reagent, see the following reviews:
• 7a Sun C.-L, Shi Z.-J. Chem. Rev. 2014; 114: 9219; and references therein
• 7b Chan TL, Wu Y, Choy PY, Kwong FY. Chem. Eur. J. 2013; 19: 15802
• 7c Mehta VP, Punji B. RSC Adv. 2013; 3: 11957
• 7d Mousseau JJ, Charette AB. Acc. Chem. Res. 2013; 46: 412
• 7e Narayan R, Manna S, Antonchick AP. Synlett 2015; 26: 1785
• 7f Narayan R, Matcha K, Antonchick AP. Chem. Eur. J. 2015; 21: 14678
• 7g Rossi R, Lessi M, Manzini C, Marianetti G, Bellina F. Adv. Synth. Catal. 2015; 357: 3777
• 7h Qin Y, Zhu L, Luo S. Chem. Rev. 2017; 117: 9433

For recent comprehensive reviews and publications, see:
• 8a Zhdankin VV, Stang PJ. Chem. Rev. 2016; 116: 3328
• 8b Zhdankin VV, Stang PJ. Chem. Rev. 2008; 108: 5299
• 8c Zhdankin VV. J. Org. Chem. 2011; 76: 1185
• 8d Silva LF. Jr, Olofsson B. Nat. Prod. Rep. 2011; 28: 1722
• 8e The Chemistry of Hypervalent Halogen Compounds . Marek I, Olofsson B, Rappoport Z. John Wiley & Sons; Chichester: 2018
• 8f Hypervalent Iodine Chemistry . In Topics in Current Chemistry, Vol. 373. Wirth T. Springer; Switzerland: 2016
• 8g Hypervalent Iodine Chemistry: Modern Developments in Organic Synthesis. In Topics in Current Chemistry, Vol. 224. Wirth T. Springer; Berlin: 2003

For our reviews and accounts, see:
• 9a Kita Y, Tohma H, Yakura T. Trends Org. Chem. 1992; 3: 113
• 9b Kita Y, Takada T, Tohma H. Pure Appl. Chem. 1996; 68: 627
• 9c Tohma H, Kita Y. Top. Curr. Chem. 2003; 224: 209
• 9d Dohi T, Ito M, Yamaoka N, Morimoto K, Fujioka H, Kita Y. Tetrahedron 2009; 65: 10797
• 9e Kita Y, Dohi T, Morimoto K. J. Synth. Org. Chem. Jpn. 2011; 69: 1241
• 9f Kita Y, Dohi T. Chem. Rec. 2015; 15: 886
• 9g Dohi T, Kita Y. Curr. Org. Chem. 2016; 20: 580
• 9h Dohi T, Kita Y. Top. Curr. Chem. 2016; 373: 1
• 9i Morimoto K, Dohi T, Kita Y. Synlett 2017; 28: 1680
• 10 Dilute peracetic acid is known as a safe and environmentally friendly oxidant that releases nontoxic acetic acid as the co-product. It is commercially available and frequently employed in industrial-scale oxidations, such as epoxidation. Furthermore, its aqueous 0.2–0.3% solution is widely used as a disinfectant in medical situations.

For early studies, see:
• 11a Tamura Y, Yakura T, Haruta J, Kita Y. J. Org. Chem. 1987; 52: 3927
• 11b Tamura Y, Yakura T, Tohma H, Kikuchi K, Kita Y. Synthesis 1989; 126
• 11c Kita Y, Yakura T, Tohma H, Kikuchi K, Tamura Y. Tetrahedron Lett. 1989; 30: 1119
• 11d Kita Y, Tohma H, Kikuchi K, Inagaki M, Yakura T. J. Org. Chem. 1991; 56: 435
• 11e Kita Y, Tohma H, Inagaki M, Hatanaka K, Kikuchi K, Yakura T. Tetrahedron Lett. 1991; 32: 2035
• 11f Kita Y, Tohma H, Inagaki M, Hatanaka K, Yakura T. J. Am. Chem. Soc. 1992; 114: 2175
• 12a Kita Y, Tohma H, Inagaki M, Hatanaka K, Yakura T. Tetrahedron Lett. 1991; 32: 4321
• 12b Kita Y, Tohma H, Hatanaka K, Takada T, Fujita S, Mitoh S, Sakurai H, Oka S. J. Am. Chem. Soc. 1994; 116: 3684

For the utility of fluoroalcohol solvents, see ref. 9b and the following reviews and accounts:
• 13a Eberson L, Hartshorn MP, Persson O, Radner F. Chem. Commun. 1996; 2105
• 13b Bégué JP, Bonnet-Delpon D, Crousse B. Synlett 2004; 18
• 13c Shuklov IA, Dubrovina NV, Boerner A. Synthesis 2007; 2925
• 13d Khaksar S. J. Fluorine Chem. 2015; 172: 51

Intramolecular cyclizations of azides:
• 14a Kita Y, Egi M, Okajima A, Ohtsubo M, Takada T, Tohma H. Chem. Commun. 1996; 1491
• 14b Kita Y, Watanabe H, Egi M, Saiki T, Fukuoka Y, Tohma H. J. Chem. Soc., Perkin Trans. 1 1998; 635
• 14c Kita Y, Egi M, Tohma H. Chem. Commun. 1999; 143
• 14d Kita Y, Egi M, Ohtsubo M, Saiki T, Okajima A, Takada T, Tohma H. Chem. Pharm. Bull. 1999; 47: 241
• 14e Kita Y, Egi M, Takada T, Tohma H. Synthesis 1999; 885

See ref. 9b and selected examples for introducing heteroatoms:
• 15a Kita Y, Takada T, Mihara S, Tohma H. Synlett 1995; 211
• 15b Kita Y, Takada T, Mihara S, Whelan BA, Tohma H. J. Org. Chem. 1995; 60: 7144
• 15c Kita Y, Egi M, Ohtsubo M, Saiki T, Takada T, Tohma H. Chem. Commun. 1996; 2225
• 15d Hamamoto H, Hata K, Nambu H, Shiozaki Y, Tohma H, Kita Y. Tetrahedron Lett. 2004; 45: 2293
• 15e Hata K, Hamamoto H, Shiozaki Y, Cämmerer SB, Kita Y. Tetrahedron 2007; 63: 4052; and references cited therein

Recent reviews on dehydrogenative aromatic C–H aminations:
• 16a Louillat M.-L, Patureau FW. Chem. Soc. Rev. 2014; 43: 901
• 16b Subramanian P, Rudolf GC, Kaliappan KP. Chem. Asian J. 2016; 11: 168
• 16c Jiao J, Murakami K, Itami K. ACS Catal. 2016; 6: 610
• 16d Kim H, Chang S. ACS Catal. 2016; 6: 2341
• 16e Henry MC, Mostafa MA. B, Sutherland A. Synthesis 2017; 49: 4586
• 16f Park Y, Kim Y, Chang S. Chem. Rev. 2017; 117: 9247
• 16g Timsina YN, Gupton BF, Ellis KC. ACS Catal. 2018; 8: 5732

Metal-free hypervalent iodine strategy:
• 16h Samanta R, Matcha K, Antonchick AP. Eur. J. Org. Chem. 2013; 5769
• 16i Samanta R, Antonchick AP. Synlett 2012; 23: 809
• 17 Kikugawa Y, Kawase M. Chem. Lett. 1990; 581
• 18a Kikugawa Y, Nagashima A, Sakamoto T, Miyazawa E, Shiiya M. J. Org. Chem. 2003; 68: 6739
• 18b Miyazawa E, Sakamoto T, Kikugawa Y. Heterocycles 2003; 59: 149
• 18c Serna S, Tellitu I, Dominguez E, Moreno I, SanMartin R. Tetrahedron 2004; 60: 6533

For other early applications, see:
• 19a Romero AG, Darlington WH, McMillan MW. J. Org. Chem. 1997; 62: 6582
• 19b Correa A, Tellitu I, Dominguez E, Moreno I, SanMartin R. J. Org. Chem. 2005; 70: 2256
• 19c Wardrop DJ, Basak A. Org. Lett. 2001; 3: 1053
• 19d Wardrop DC, Zhang W. Org. Lett. 2001; 3: 2353

For reviews on catalytic utilizations of hypervalent iodine reagents, see:
• 20a Richardson RD, Wirth T. Angew. Chem. Int. Ed. 2006; 45: 4402
• 20b Ochiai M, Miyamoto K. Eur. J. Org. Chem. 2008; 4429
• 20c Dohi T, Kita Y. Chem. Commun. 2009; 2073
• 20d Yusubov MS, Zhdankin VV. Mendeleev Commun. 2010; 20: 2073
• 20e Singh FV, Wirth T. Chem. Asian J. 2014; 9: 950

For the first report of C–N bond-forming reaction using a catalytic amount of hypervalent iodine, see:
• 21a Dohi T, Maruyama A, Minamitsuji Y, Takenaga N, Kita Y. Chem. Commun. 2007; 1224
• 21b Moroda A, Togo H. Synthesis 2008; 1257

For early studies, see:
• 22a Alcock NW, Waddington TC. J. Chem. Soc. 1963; 4103
• 22b Gallos J, Varvoglis A, Alcock NW. J. Chem. Soc., Perkin Trans. 1 1985; 757

We have recently met the notably high reactivity of μ-oxo-bridged PIFA dimer in organic solvents as well as in water, see:
• 23a Dohi T, Uchiyama T, Yamashita D, Washimi N, Kita Y. Tetrahedron Lett. 2011; 52: 2212
• 23b Takenaga N, Uchiyama T, Kato D, Fujioka H, Dohi T, Kita Y. Heterocycles 2011; 82: 1327
• 23c Dohi T, Nakae T, Takenaga N, Uchiyama T, Fukushima K, Fujioka H, Kita Y. Synthesis 2012; 44: 1183
• 24 Dohi T, Takenaga N, Fukushima K, Uchiyama T, Kato D, Shiro M, Fujioka H, Kita Y. Chem. Commun. 2010; 46: 7697
• 25 For utilizations of our μ-oxo catalysts in other reactions, see: Ito M, Kubo H, Itani I, Morimoto K, Dohi T, Kita Y. J. Am. Chem. Soc. 2013; 135: 14078 ; see also ref. 26
• 26a Dohi T, Nakae T, Ishikado Y, Kato D, Kita Y. Org. Biomol. Chem. 2011; 9: 6899
• 26b Dohi T, Kato D, Hyodo R, Yamashita D, Shiro M, Kita Y. Angew. Chem. Int. Ed. 2011; 50: 3784
• 26c Dohi T, Mochizuki E, Yamashita D, Miyazaki K, Kita Y. Heterocycles 2014; 88: 245

X-ray crystal structure data of PIFA:
• 27a Stergioudis GA, Kokkou SC, Bozopoulos AP, Rentzeperis PJ. Acta Crystallogr., Sect. C 1984; 40: 877

PIDA:
• 27b Lee C.-K, Mak TC. W, Li W.-K. Acta Crystallogr., Sect. B 1977; 33: 1620
• 27c The reported bond lengths of iodine(III) ligands in the hypervalent iodine reagents, PIDA and PIFA as well as μ-oxo-bridged PIFA dimer and our biaryl alternative Ib (see Figure 1 for the structures), are summarized in Table 2 below.

The existence of strong secondary bondings between the iodine atoms and the ligand’s carbonyl oxygens appears in the structure, which was confirmed by the lower shift of carbonyl frequencies for the μ-oxo PIFA in the infrared resonance spectra compared to that of PIFA. These observations clearly account for the enhanced cationic character of the iodine center, see:
• 28a Alcock NW, Countryman RM, Esperas S, Sawyer JF. J. Chem. Soc., Dalton Trans. 1979; 854
• 28b Alcock NW, Harrison WD. J. Chem. Soc., Dalton Trans. 1984; 1709
• 28c Bell R, Morgan KJ. J. Chem. Soc. 1960; 1209
• 29 Samanta R, Bauer JO, Strohmann C, Antonchick AP. Org. Lett. 2012; 14: 5518
• 30a Minamitsuji Y, Kato D, Fujioka H, Dohi T, Kita Y. Aust. J. Chem. 2009; 62: 648
• 30b Dohi T, Yamaoka N, Itani I, Kita Y. Aust. J. Chem. 2011; 64: 529
• 31 The TON of a catalyst, 1,2-diiodobenzene, at the 4 mol% loading reached 18 times for the reaction between the same substrates (toluene 2a, 15 equiv) in HFIP/DCE (1:1), see: Lucchetti N, Scalone M, Fantasia S, Muñiz K. Adv. Synth. Catal. 2016; 358: 2093

For utilities of N-methoxy anilides for unique transformations, see:
• 32a Kikugawa Y, Shimada M. J. Chem. Soc., Chem. Commun. 1989; 1450
• 32b Matsumoto K, Kato M, Sakamoto T, Kikugawa Y. J. Chem. Res., Synop. 1995; 34
• 32c Nakamura I, Jo T, Ishida Y, Tashiro H, Terada M. Org. Lett. 2017; 19: 3059
• 32d Ishida Y, Nakamura I, Terada M. J. Am. Chem. Soc. 2018; 140: 8629; and references cited therein

See ref 9d and:
• 33a Dohi T, Ito M, Morimoto K, Minamitsuji Y, Takenaga N, Kita Y. Chem. Commun. 2007; 4152
• 33b Ito M, Ogawa C, Yamaoka N, Fujioka H, Dohi T, Kita Y. Molecules 2010; 15: 1918
• 33c Ito M, Itani I, Toyoda Y, Morimoto K, Dohi T, Kita Y. Angew. Chem. Int. Ed. 2012; 51: 12555

For the reactivities of diaryliodonium(III) salt, see:
• 34a Merritt EA, Olofsson B. Angew. Chem. Int. Ed. 2009; 48: 9052
• 34b Yusubov MS, Maskaev AV, Zhdankin VV. ARKIVOC 2011; (i): 370
• 34c Olofsson B. Top. Curr. Chem. 2016; 373: 135
• 34d Stuart DR. Chem. Eur. J. 2017; 23: 15852
• 34e Yoshimura A, Saito A, Zhdankin VV. Chem. Eur. J. 2018; 24: 15156
• 34f Stang PJ, Zhdankin VV. Chem. Rev. 1996; 96: 1123
• 34g Müller U. Trends Photochem. Photobiol. 1999; 5: 117
• 35 For ortho-directing effect of amide-containing reagent involving pseudo-cyclic intermediate in electrophilic aromatic substitutions, see: Shen H, Vollhardt KP. C. Synlett 2012; 23: 208

Transition-metal-catalyzed oxidative amidations for aromatic hydrocarbons with stoichiometric hypervalent iodine reagent, see:
• 36a Shrestha R, Mukherjee P, Tan Y, Litman ZC, Harwig JF. J. Am. Chem. Soc. 2013; 135: 8480
• 36b Marchetti L, Kantak A, Davis R, DeBoef B. Org. Lett. 2015; 17: 358
• 36c Berzina B, Sokolovs I, Suna E. ACS Catal. 2015; 5: 7008
• 36d Ito E, Fukushima T, Kawakami T, Murakami K, Itami K. Chem 2017; 2: 383

The combination of transition metal ([Co]) with photocatalyst:
• 36e Niu L, Yi H, Wang S, Liu T, Liu J, Lei A. Nat. Commun. 2017; 8: 14226

The use of 0.5 mol% amount of iridium-based photocatalyst was reported, while the product yields was up to 52% in this case:
• 36f Kim H, Kim T, Lee DG, Roh SW, Lee C. Chem. Commun. 2014; 50: 9273
• 37a Brasche G, García-Fortanet J, Buchwald SL. Org. Lett. 2008; 10: 2207

For a recent review of transition-metal-catalyzed ortho C–H functionalizations of aniline derivatives, see:
• 37b Leitch JA, Frost CG. Synthesis 2018; 50: 2693
• 38 Antonchick reported this type of coupling reaction using PIDA as a stoichiometric amount: Antonchick AP, Samanta R, Kulikov K, Lategahn J. Angew. Chem. Int. Ed. 2011; 50: 8605

Representative examples:
• 39a Kim HJ, Kim J, Cho SH, Chang S. J. Am. Chem. Soc. 2011; 133: 16382
• 39b Kantak AA, Potavathri S, Barham RA, Romano KM, DeBoef B. J. Am. Chem. Soc. 2011; 133: 19960
• 39c Samanta R, Lategahn I, Antonchick AP. Chem. Commun. 2012; 48: 3194
• 39d Manna S, Serebrennikova PO, Utepova IA, Antonchick AP, Chupakhin ON. Org. Lett. 2015; 17: 4588
• 39e Pialat A, Bergès J, Sabourin A, Vinck R, Liégault B, Taillefer M. Chem. Eur. J. 2015; 21: 10014
• 39f Mondal S, Samanta S, Jana S, Hajra A. J. Org. Chem. 2017; 82: 4504
• 39g Zhao F, Sun T, Sun H, Xi G, Sun K. Tetrahedron Lett. 2017; 58: 3132
• 39h Maiti S, Mal P. J. Org. Chem. 2018; 83: 1340

For diaryliodonium(III) salt mediated C–N coupling strategies, see:
• 40a Carroll MA, Wood RA. Tetrahedron 2007; 63: 11349
• 40b Riedmueller S, Nachtsheim BJ. Synlett 2015; 26: 651
• 40c Yang Y, Wu X, Han J, Mao S, Quian X, Wang L. Eur. J. Org. Chem. 2014; 6854
• 40d Tinnis F, Stridfeldt E, Lundberg H, Adolfsson H, Olofsson B. Org. Lett. 2015; 17: 2688
• 40e Lucchetti N, Scalone M, Fantasia S, Muñiz K. Angew. Chem. Int. Ed. 2016; 55: 13335
• 40f Sandtorv AH, Stuart DR. Angew. Chem. Int. Ed. 2016; 55: 15812
• 40g Basu S, Sandtorv AH, Stuart DR. Beilstein J. Org. Chem. 2018; 14: 1034
• 40h Purkait N, Kervefors G, Linde E, Olofsson B. Angew. Chem. Int. Ed. 2018; 57: 11427
• 41a Morimoto K, Ohnishi Y, Nakamura A, Sakamoto K, Dohi T, Kita Y. Asian J. Org. Chem. 2014; 3: 382
• 41b Morimoto K, Ogawa R, Koseki D, Takahashi Y, Dohi T, Kita Y. Chem. Pharm. Bull. 2015; 63: 819

Related μ-oxo-bridged chiral hypervalent iodine catalysts:
• 42a Dohi T, Maruyama A, Takenage N, Senami K, Minamitsuji Y, Fujioka H, Cämmerer S, Kita Y. Angew. Chem. Int. Ed. 2008; 47: 3787
• 42b Dohi T, Takenaga N, Nakae T, Toyoda Y, Yamasaki M, Shiro M, Fujioka H, Maruyama A, Kita Y. J. Am. Chem. Soc. 2013; 135: 4558
• 42c Suzuki S, Kamo T, Fukushi K, Hiramatsu T, Tokunaga E, Dohi T, Kita Y, Shibata N. Chem. Sci. 2014; 5: 2754
• 42d Ogasawara M, Sasa H, Hu H, Amano Y, Nakajima H, Takenaga N, Nakajima K, Kita Y, Takahashi T, Dohi T. Org. Lett. 2017; 19: 4102
• 42e Dohi T, Sasa H, Miyazaki K, Fujitake M, Takenaga N, Kita Y. J. Org. Chem. 2017; 82: 11954
• 43 Utilizing our spirobiindane catalysts (see refs 42a and 42b), Cai and co-workers recently developed intramolecular oxidative C–N cyclizations accompanying asymmetric desymmetrization of the substrates, see: Ding Q, He H, Cai Q. Org. Lett. 2018; 20: 4554
• 44a Kawase M, Kitamura T, Kikugawa Y. J. Org. Chem. 1989; 54: 3394
• 44b Miyata O, Koizumi T, Asai H, Iba R, Naito T. Tetrahedron 2004; 60: 3893
• 44c Xie W, Yang J, Wang B, Li B. J. Org. Chem. 2014; 79: 8278
• 44d Brosse N, Pinto M, Jamart-Gregoire B. Eur. J. Org. Chem. 2003; 4757
• 45a Tohma H, Morioka H, Takizawa S, Arisawa M, Kita Y. Tetrahedron 2001; 57: 345
• 45b Tohma H, Iwata M, Maegawa T, Kita Y. Tetrahedron Lett. 2002; 43: 9241