Synlett 2015; 26(05): 580-603
DOI: 10.1055/s-0034-1378945
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© Georg Thieme Verlag Stuttgart · New York

How the Structural Elucidation of the Natural Product Stephanosporin Led to New Developments in Aryl Radical and Medicinal Chemistry

Stefanie K. Fehler, Markus R. Heinrich*
  • Department of Chemistry and Pharmacy, Pharmaceutical Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Schuhstraße 19, 91052 Erlangen, Germany   Fax: +49(9131)8522585   eMail: Markus.Heinrich@fau.de
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Publikationsverlauf

Received: 05. November 2014

Accepted after Revision: 25. November 2014

Publikationsdatum:
17.Februar 2015 (eFirst)

Dedicated to Prof. Dr. Wolfgang Steglich, Prof. Dr. Peter Spiteller, and Dr. Martin Lang.

Abstract

The intent of this account is to provide a focused overview of recent developments in aryl radical chemistry, especially extensions and applications of the Meerwein arylation and the Gomberg–Bachmann reaction. Although most of the reactions and methods described were discovered on the basis of earlier findings made by our group or logically depend on newly discovered reactivities or mechanistic principles, the rapid evolution of radical chemistry can nevertheless be traced back to the behavior of the natural product stephanosporin, which is capable of liberating 2-chloro-4-nitrophenol via an aryl radical intermediate.

1 Introduction to Aryl Radical Chemistry

2 Stephanosporin

3 Low-Temperature Radical Initiators That Generate Aryl Radicals

4 Alkene Functionalizations

4.1 Carboamination

4.1.1 Carbodiazenylation Reactions

4.1.2 Carbonitrosation Reactions

4.2 Carbooxygenation

4.3 Carbofluorination

4.4 Allylation and Vinylation

4.5 Reductive Arylation and Labelling with Fluorine-18

4.6 Cascade Reactions

5 Arene Functionalizations

5.1 Arylations with Aryldiazonium Salts

5.2 Arylations with Arylhydrazines

5.3 Acid- and Base-Induced Arylations

6 Summary and Outlook

 
  • References

  • 1 Krätz O. Chem. Unserer Zeit 1976; 10: 42

    • For selected articles related to the structure of the natural product stephanosporin, see:
    • 2a Griess P. Justus Liebigs Ann. Chem. 1859; 109: 286
    • 2b Griess P. Justus Liebigs Ann. Chem. 1860; 113: 201
    • 3a Sandmeyer T. Chem. Ber. 1896; 17: 1633
    • 3b Minisci F, Fontana F, Vismara E. Gazz. Chim. Ital. 1993; 123: 9
    • 3c Merkushev EB. Synthesis 1988; 923
    • 4a Pschorr R. Chem. Ber. 1896; 29: 496
    • 4b Leake PH. Chem. Rev. 1956; 56: 27
    • 4c Laali KK, Shokouhimehr M. Curr. Org. Synth. 2009; 6: 193
  • 5 Gomberg M. J. Am. Chem. Soc. 1900; 22: 757
    • 6a Gomberg M, Bachmann WE. J. Am. Chem. Soc. 1924; 46: 2339
    • 6b Dermer OC, Edmison MT. Chem. Rev. 1957; 57: 77
  • 7 Meerwein H, Büchner E, van Emster K. J. Prakt. Chem. 1939; 152: 237
  • 8 The data presented in Figure 1 were obtained by means of a reference search in SciFinder using the key words given in the figure.
  • 10 For a comprehensive review on diazonium salts as sources of aryl radicals, see: Galli C. Chem. Rev. 1988; 88: 765
    • 11a Cohen T, Lewarchik RJ, Tarino JZ. J. Am. Chem. Soc. 1974; 96: 7753
    • 11b Cohen T, Dietz AG. Jr, Miser JR. J. Org. Chem. 1977; 42: 2053
  • 12 Waters WA. The Chemistry of Free Radicals . Clarendon Press; Oxford; 1946
  • 13 Zollinger H. Acc. Chem. Res. 1973; 6: 335

    • For reviews on the Meerwein arylation, see:
    • 14a Rondestvedt CS. Jr. Org. React. (N. Y.) 1976; 24: 225
    • 14b Heinrich MR. Chem. Eur. J. 2009; 15: 820
  • 16 Pratsch G, Heinrich MR. Top. Curr. Chem. 2012; 320: 33
    • 17a Hari DP, König B. Angew. Chem. Int. Ed. 2013; 52: 4734
    • 17b Mo F, Dong G, Zhang Y, Wang J. Org. Biomol. Chem. 2013; 11: 1582
    • 17c Majek M, Filace F, Jacobi von Wangelin A. Beilstein J. Org. Chem. 2014; 10: 981
  • 18 Pinson J In Aryl Diazonium Salts: New Coupling Agents in Polymer and Surface Science. Chehimi MM. Wiley-VCH; Weinheim; 2012. Chap. 1, 1
  • 19 Lang M, Spiteller P, Hellwig V, Steglich W. Angew. Chem. Int. Ed. 2001; 40: 1704
  • 20 Huang PC, Kosower EM. J. Am. Chem. Soc. 1967; 89: 3910
    • 21a Lang M. Ph.D. Thesis. Ludwig-Maximilians-Universität München; Germany; 2002
    • 21b Spiteller P. Chem. Eur. J. 2008; 14: 9100

      For reviews on triethylborane, see:
    • 22a O’Mahony G. Synlett 2004; 572
    • 22b Ollivier C, Renaud P. Chem. Rev. 2001; 101: 3415

      For recent articles on the use of triethylborane as an initiator, see:
    • 23a Yoshimitsu T, Arano Y, Nagaoka H. J. Am. Chem. Soc. 2005; 127: 11610
    • 23b Yamada K.-I, Konishi T, Nakano M, Fujii S, Cadou R, Yamamoto Y, Tomioka K. J. Org. Chem. 2012; 77: 1547
    • 23c Pitts CR, Ling B, Woltornist R, Liu R, Lectka T. J. Org. Chem. 2014; 79: 8895
    • 24a Mirviss SB. J. Org. Chem. 1967; 32: 1713
    • 24b Crawford CL, Barnes MJ, Peterson RA, Wilmarth WR, Hyder ML. J. Organomet. Chem. 1999; 581: 194
    • 25a Kita Y, Matsugi M In Radicals in Organic Synthesis . Vol. 1, Chap. 1. Renaud P, Sibi MP. Wiley-VCH; Weinheim; 2001: 1
    • 25b Garden SJ, Avila DV, Beckwith AL. J, Bowry VW, Ingold KU, Lusztyk J. J. Org. Chem. 1996; 61: 805
    • 26a Seifert KG, Gerhart F. Tetrahedron Lett. 1974; 15: 829
    • 26b Russell GA, Bridger RF. Tetrahedron Lett. 1963; 737
  • 27 Baralle A, Fensterbank L, Goddard J.-P, Ollivier C. Chem. Eur. J. 2013; 19: 10809
    • 28a Cao L, Li C. Tetrahedron Lett. 2008; 49: 7380
    • 28b See also ref. 43.
    • 29a Hardie RL, Thomson RH. J. Chem. Soc. 1957; 2512
    • 29b Braslau R, Burrill LC. II, Siano M, Naik N, Howden RK, Mahal LK. Macromolecules 1997; 30: 6445
    • 29c See also ref. 72a.
  • 30 For the oxidation of phenyl hydrazines at low temperatures, see: Aylward JB. J. Chem. Soc. C 1969; 1663
  • 31 Braslau R, Burrill LC. II, Mahal LK, Wedeking T. Angew. Chem. Int. Ed. 1997; 36: 237
  • 32 Kosower EM, Miyadera T. J. Med. Chem. 1972; 15: 307
  • 33 Al Adel I, Salami BA, Levisalles J, Rudler H. Bull. Soc. Chim. Fr. 1976; 934
    • 34a Citterio A, Minisci F, Albinati A, Bruckner S. Tetrahedron Lett. 1980; 21: 2909
    • 34b Citterio A, Ramperti M, Vismara E. J. Heterocycl. Chem. 1981; 18: 763
    • 34c Citterio A, Minisci F, Vismara E. J. Org. Chem. 1982; 47: 81
    • 34d Citterio A, Minisci F. J. Org. Chem. 1982; 47: 1759
    • 34e Minisci F, Coppa F, Fontana F, Pianese G, Zhao L. J. Org. Chem. 1992; 57: 3929

      For review articles on nitrogen-centered radical scavengers, see:
    • 35a Höfling SB, Heinrich MR. Synthesis 2011; 173
    • 35b Ollivier C, Renaud P In Radicals in Organic Synthesis . Vol. 2, Chap. 2.1. Renaud P, Sibi MP. Wiley-VCH; Weinheim; 2001: 93
  • 36 Heinrich MR, Blank O, Wetzel A. J. Org. Chem. 2007; 72: 476
    • 37a Heinrich MR, Blank O, Wölfel S. Org. Lett. 2006; 8: 3323
    • 37b Heinrich MR, Blank O, Wölfel S. Synfacts 2006; 1045
  • 38 Blank O, Wetzel A, Ullrich D, Heinrich MR. Eur. J. Org. Chem. 2008; 3179
  • 39 Kralj A, Wetzel A, Mahmoudian S, Stamminger T, Tschammer N, Heinrich MR. Bioorg. Med. Chem. Lett. 2011; 21: 5446
  • 40 Tomin A, Hornyánszky G, Kupai K, Dorkó Z, Ürge L, Darvas F, Poppe L. Process Biochem. 2010; 45: 859
    • 41a Casarosa P, Menge WM, Minisini R, Otto C, van Heteren J, Jongejan A, Timmerman H, Moepps B, Kirchhoff F, Mertens T, Smit MJ, Leurs R. J. Biol. Chem. 2003; 278: 5172
    • 41b Vischer HF, Hulshof JW, Hulscher S, Fratantoni SA, Verheij MH, Victorina J, Smit MJ, de Esch IJ. P, Leurs R. Bioorg. Med. Chem. 2010; 18: 675
  • 43 Brunner H, Blüchel C, Doyle MP. J. Organomet. Chem. 1997; 541: 89
  • 44 Heinrich MR, Blank O, Wetzel A. Synlett 2006; 3352
  • 45 Dietz FR, Prechter A, Gröger H, Heinrich MR. Tetrahedron Lett. 2011; 52: 655
  • 46 Prechter A, Gröger H, Heinrich MR. Org. Biomol. Chem. 2012; 10: 3384
  • 47 For the deactivating effect of acetic acid on enzymes, see: Romero MD, Calvo L, Alba C, Daneshfar A. J. Biotechnol. 2007; 127: 269
  • 48 Steinig AG, Spero DM. J. Org. Chem. 1999; 64: 2406
  • 49 Porter NA, Marnett LJ. J. Am. Chem. Soc. 1973; 95: 4361
  • 50 The feasibility of a comparable racemization through homolytic cleavage and recombination has recently been shown, see: Prechter A, Heinrich MR. Eur. J. Org. Chem. 2013; 5585

    • For pioneering work, see:
    • 51a Roberts BP, Winter JN. J. Chem. Soc., Perkin Trans. 2 1979; 1353
    • 51b Roberts BP, Dang H.-S. J. Chem. Soc., Perkin Trans. 1 1996; 1493
    • 52a Ollivier C, Renaud P. J. Am. Chem. Soc. 2000; 122: 6496
    • 52b Cren S, Schär P, Renaud P, Schenk K. J. Org. Chem. 2009; 74: 2942
    • 52c Weidner K, Giroult A, Panchaud P, Renaud P. J. Am. Chem. Soc. 2010; 132: 17511
  • 53 Blank O, Heinrich MR. Eur. J. Org. Chem. 2006; 4331
    • 54a Walling C. Acc. Chem. Res. 1975; 8: 125
    • 54b Schreiber SL. J. Am. Chem. Soc. 1980; 102: 6163
    • 54c Dichtl A, Seyfried M, Schoening K.-U. Synlett 2008; 1877
  • 55 Blank O, Raschke N, Heinrich MR. Tetrahedron Lett. 2010; 51: 1758
  • 56 Hartung J. Chem. Rev. 2009; 109: 4500
  • 57 Zavitsas A. J. Org. Chem. 2008; 73: 9022
    • 58a Okamoto T, Oka S. J. Chem. Soc. Chem. Commun. 1984; 289
    • 58b Patel VF, Pattenden G. Tetrahedron Lett. 1987; 28: 1451
    • 58c Ghosez A, Göbel T, Giese B. Chem. Ber. 1988; 121: 1807
    • 58d Veit A, Giese B. Synlett 1990; 166
    • 58e Kijima M, Yamashita H, Sato T. J. Organomet. Chem. 1992; 426: 399
    • 58f Okamoto T, Kobayashi K, Oka S, Tanimoto S. J. Org. Chem. 1987; 52: 5089
    • 58g Patel VF, Pattenden G. J. Chem. Soc., Perkin Trans. 1 1990; 2703

      For the reversible binding of NO to complexes of iron(II) in aqueous solution, see:
    • 59a Schneppensieper T, Finkler S, Czap A, van Eldik R, Heus M, Nieuwenhuizen P, Wreesmann C, Abma W. Eur. J. Inorg. Chem. 2001; 491
    • 59b Schneppensieper T, Wanat A, Stochel G, van Eldik R. Inorg. Chem. 2002; 41: 2565
    • 59c Wanat A, Schneppensieper T, Stochel G, van Eldik R, Bill E, Wieghardt K. Inorg. Chem. 2002; 41: 4
  • 60 de Salas C, Blank O, Heinrich MR. Chem. Eur. J. 2011; 17: 9306
  • 61 For the purification of highly concentrated NO x gas (206000 ppm) from a metal dissolution process, see: Yasuda M, Tsugita N, Ito K, Yamauchi S, Glomm WR, Tsuji I, Asano H. Environ. Sci. Technol. 2011; 45: 1840
  • 62 de Salas C, Heinrich MR. Green Chem. 2014; 16: 2982
    • 63a Ganushchak NI, Grishchuk BD, Dombrovskii AV. J. Org. Chem. USSR (Engl. Transl.) 1973; 9: 1030
    • 63b Grishchuk BD, Gorbovoi PM, Ganushchak NI, Dombrovskii AV. Russ. Chem. Rev. 1994; 63: 257

      For related radical carbooxygenation of alkenes with alkyl radicals and nitroxides, see:
    • 64a Herrera AJ, Studer A. Synthesis 2005; 1389
    • 64b Wetter C, Studer A. Chem. Commun. 2004; 174
    • 64c Wetter C, Jantos K, Woithe K, Studer A. Org. Lett. 2003; 5: 2899
  • 65 For comparable Kharash–Sosnovsky-type allylic C–H oxidations, see: Katsuki T. In Radicals in Organic Synthesis . Vol. 2, Chap. 2.2. Renaud P, Sibi MP. Wiley-VCH; Weinheim; 2001: 113
  • 66 Heinrich MR, Kirschstein M. Tetrahedron Lett. 2006; 47: 2115
  • 67 Ikeda T, Tsutsumi O. Science 1995; 268: 1873
  • 68 For the kinetics of nitroxide radical trapping and solvent effects, see: Beckwith AL. J, Bowry VW, Ingold KU. J. Am. Chem. Soc. 1992; 114: 4983
  • 69 Heinrich MR, Wetzel A, Kirschstein M. Org. Lett. 2007; 9: 3833
  • 70 Hartmann M, Li Y, Studer A. J. Am. Chem. Soc. 2012; 134: 16516
  • 71 Li Y, Studer A. Angew. Chem. Int. Ed. 2012; 51: 8221
    • 72a Taniguchi T, Zaimoku H, Ishibashi H. Chem. Eur. J. 2011; 17: 4307
    • 72b Dickschat A, Studer A. Org. Lett. 2010; 12: 3972
  • 73 Kindt S, Jasch H, Heinrich MR. Chem. Eur. J. 2014; 20: 6251

    • For closely related carbofluorination reactions, see:
    • 74a Barker TJ, Boger DL. J. Am. Chem. Soc. 2012; 134: 13588
    • 74b Wang H, Guo L.-N, Duan X.-H. Chem. Commun. 2014; 50: 7382
    • 75a Sibi MP, Landais Y. Angew. Chem. Int. Ed. 2013; 52: 3570
    • 75b Ma J.-A, Li S. Org. Chem. Front. 2014; 1: 712
    • 75c Rueda-Becerril M, Sazepin CC, Leung JC. T, Okbinoglu T, Kennepohl P, Paquin J.-F, Sammis GM. J. Am. Chem. Soc. 2012; 134: 4026

      Selectfluor (1-chloromethyl-4-fluoro-1,4-diazoniabicyclo-[2.2.2]octane ditetrafluoroborate); see:
    • 76a Singh RP, Shreeve JM. Acc. Chem. Res. 2004; 37: 31
    • 76b Nyffeler PT, Durón SG, Burkart MD, Vincent SP, Wong C.-H. Angew. Chem. Int. Ed. 2005; 44: 192
  • 77 Kindt S, Heinrich MR. Chem. Eur. J. 2014; 20: 15344
  • 78 Ek F, Axelsson O, Wistrand L.-G, Frejd T. J. Org. Chem. 2002; 67: 6376
    • 79a Wagner PJ, Sedon JH, Lindstrom MJ. J. Am. Chem. Soc. 1978; 100: 2579
    • 79b Migita T, Kosugi M, Takayama K, Nakagawa Y. Tetrahedron 1973; 29: 51
  • 80 Heinrich MR, Blank O, Ullrich D, Kirschstein M. J. Org. Chem. 2007; 72: 9609
    • 81a Citterio A, Vismara E. Synthesis 1980; 291
    • 81b Citterio A, Cominelli A, Bonavoglia F. Synthesis 1986; 308
  • 82 Tashtoush HI, Sustmann R. Chem. Ber. 1993; 126: 1759
  • 83 Murphy JA In Radicals in Organic Synthesis . Vol. 1, Chap. 2.7. Renaud P, Sibi MP. Wiley-VCH; Weinheim; 2001: 298
  • 84 Cai L, Lu S, Pike VW. Eur. J. Org. Chem. 2008; 2853
  • 85 Patt JT, Patt M. J. Labelled Compd. Radiopharm. 2002; 45: 1229

    • For earlier syntheses of 18F-labeled aryldiazonium salts and anilines, see:
    • 86a Feliu AJ. J. Labelled Compd. Radiopharm. 1988; 25: 1245
    • 86b Olma S, Ermert J, Coenen HH. J. Labelled Compd. Radiopharm. 2006; 49: 1037
  • 87 Hultsch C, Blank O, Wester H.-J, Heinrich MR. Tetrahedron Lett. 2008; 49: 1881
  • 88 Yang Y, Cui M. Eur. J. Med. Chem. 2014; 87: 703
  • 89 Höfling SB, Hultsch C, Wester H.-J, Heinrich MR. Tetrahedron 2008; 64: 11846
  • 90 Chen Z, Chen Z, Jiang Y, Hu W. Tetrahedron 2005; 61: 1579
    • 91a Hocke C, Maschauer S, Hübner H, Löber S, Utz W, Kuwert T, Gmeiner P, Prante O. ChemMedChem 2010; 5: 941
    • 91b Hocke C, Cumming P, Maschauer S, Kuwert T, Gmeiner P, Prante O. Nucl. Med. Biol. 2014; 41: 223
  • 92 Höfling SB, Maschauer S, Hübner H, Gmeiner P, Wester H.-J, Prante O, Heinrich MR. Bioorg. Med. Chem. Lett. 2010; 20: 6933
  • 93 Obushak ND, Ganushchak NI, Matiichuk VS. Russ. J. Org. Chem. 1996; 32: 766
    • 94a Togo H, Kikuchi O. Tetrahedron Lett. 1988; 29: 4133
    • 94b Togo H, Kikuchi O. Heterocycles 1989; 28: 373
    • 95a Fu W, Xu F, Fu Y, Zhu M, Yu J, Xu C, Zou D. J. Org. Chem. 2013; 78: 12202
    • 95b Xiao T, Dong X, Tang Y, Zhou L. Adv. Synth. Catal. 2012; 354: 3195
    • 95c Tang S, Zhou D, Wang Y.-C. Eur. J. Org. Chem. 2014; 3656
  • 96 Jasch H, Landais Y, Heinrich MR. Chem. Eur. J. 2013; 19: 8411
    • 97a Beadle JR, Korzeniowski SH, Rosenberg DE, Garcia-Slanga BJ, Gokel GW. J. Org. Chem. 1984; 49: 1594
    • 97b Campo MA, Zhang H, Yao T, Ibdah A, McCulla RD, Huang Q, Zhao J, Jenks WS, Larock RC. J. Am. Chem. Soc. 2007; 129: 6298
  • 98 Wetzel A, Ehrhardt V, Heinrich MR. Angew. Chem. Int. Ed. 2008; 47: 9130
  • 99 Jensen AE, Knochel P. J. Organomet. Chem. 2002; 653: 122
  • 100 For the first studies on titanium(III)-mediated radical arylations of phenols, see: Caronna T, Ferrario F, Servi S. Tetrahedron Lett. 1979; 657
  • 101 Wetzel A, Pratsch G, Kolb R, Heinrich MR. Chem. Eur. J. 2010; 16: 2547
  • 102 Knör S, Laufer B, Kessler H. J. Org. Chem. 2006; 71: 5625
    • 104a Vincent JP, Mazella J, Kitabgi P. Trends Pharmacol. Sci. 1999; 20: 302
    • 104b Dobner PR. Peptides 2006; 27: 2405
  • 105 The activity of neurotensin is mediated by its C-terminal 6 amino acid fragment NT(8–13): St-Pierre S, Lalonde J.-M, Gendreau M, Quirion R, Regoli D, Rioux F. J. Med. Chem. 1981; 24: 370
  • 106 Pratsch G, Unfried JF, Einsiedel J, Plomer M, Hübner H, Gmeiner P, Heinrich MR. Org. Biomol. Chem. 2011; 9: 3746
  • 107 For highly selective NTS2 ligands, see: Einsiedel J, Held C, Hervet M, Plomer M, Tschammer N, Hübner H, Gmeiner P. J. Med. Chem. 2011; 54: 2915
  • 108 Kuglstatter A, Stahl M, Peters J.-U, Huber W, Stihle M, Schlatter D, Benz J, Ruf A, Roth D, Enderle T, Hennig M. Bioorg. Med. Chem. Lett. 2008; 18: 1304
  • 109 Fehler SK, Pratsch G, Huber W, Gast A, Hochstrasser R, Hennig M, Heinrich MR. Tetrahedron Lett. 2012; 53: 2189
  • 110 Kralj A, Kurt E, Tschammer N, Heinrich MR. ChemMedChem 2014; 9: 151
  • 111 PathDetect In Vivo Signal Transduction Pathway trans-Reporting Systems: Instruction Manual. Agilent Technologies; Santa Clara; 2011. Revision B.01: http://www.chem.agilent.com/ Library/usermanuals/Public/219000.pdf (accessed Dec. 5, 2014)
  • 112 Hammer SG, Heinrich MR. Tetrahedron 2014; 70: 8114
  • 113 Shi Z, Zhang C, Li S, Pan D, Ding S, Cui Y, Jiao N. Angew. Chem. Int. Ed. 2009; 48: 4572
    • 114a Colonge J, Chambard R. Bull. Soc. Chim. Fr. 1953; 982
    • 114b Johnston KM, Luker RM, Williams GH. J. Chem. Soc., Perkin Trans. 1 1972; 13: 1648
    • 114c Inglis SR, Stojkoski C, Branson KM, Cawthray JF, Fritz D, Wiadrowski E, Pyke SM, Booker GW. J. Med. Chem. 2004; 47: 5405
  • 115 Meyer V. Ber. Dtsch. Chem. Ges. 1887; 20: 3289
    • 116a Griesbeck AG, Zimmermann E In Science of Synthesis . Vol. 28, Chap. 28.11. Griesbeck AG. Thieme; Stuttgart; 2006: 807
    • 116b Sander W, Bucher GF, Komnick P, Morawietz J, Bubenitschek P, Jones PG, Chrapkowski A. Chem. Ber. 1993; 126: 2101
    • 116c Arnold BR, Scaiano JC, Bucher G, Sander W. J. Org. Chem. 1992; 57: 6469
  • 117 Pratsch G, Anger CA, Ritter K, Heinrich MR. Chem. Eur. J. 2011; 17: 4104
  • 118 Pratsch G, Wallaschkowski T, Heinrich MR. Chem. Eur. J. 2012; 18: 11555
  • 119 Rüchardt C, Merz E. Tetrahedron Lett. 1964; 2431
  • 120 For a characterization of aryl diazotates by 1H NMR spectroscopy, see: Elofson RM, Cyr N, Laidler JK. Tetrahedron Lett. 1990; 31: 7205
    • 121a Demir AS, Findik H. Tetrahedron 2008; 64: 6196
    • 121b Demir AS, Reis Ö, Emrullahoğlu M. Tetrahedron 2002; 58: 8055
    • 121c Chen Z.-X, Wang G.-W. J. Org. Chem. 2005; 70: 2380
  • 122 Jasch H, Scheumann J, Heinrich MR. J. Org. Chem. 2012; 77: 10699
  • 123 Hofmann J, Jasch H, Heinrich MR. J. Org. Chem. 2014; 79: 2314
  • 124 Eicken K, Rack M, Wetterich F, Ammermann E, Lorenz G, Strathmann S. DE 19735224, 1999 ; Chem. Abstr. 1999, 130, 182464
  • 125 Jörges W, Heinrich J.-D, Lantzsch R. WO 2006024388, 2006 ; Chem. Abstr. 2006, 144, 253890
  • 126 Dietz J, Strathmann S, Stierl R, Montag J. WO 2007128756, 2007 ; Chem. Abstr. 2007, 147, 516420
  • 128 Dey BB, Govindachari TR, Rajagopalan SC. Curr. Sci. 1946; 15: 161
  • 129 Höfling SB, Bartuschat AL, Heinrich MR. Angew. Chem. Int. Ed. 2010; 49: 9769
  • 130 Jasch H, Höfling S, Heinrich MR. J. Org. Chem. 2012; 77: 1520
  • 131 Fehler SK, Höfling SB, Bartuschat AL, Maschauer S, Tschammer N, Hübner H, Gmeiner P, Prante O, Heinrich MR. Chem. Eur. J. 2014; 20: 370
    • 132a Runyon SP, Carroll FI. . Current Topics in Medicinal Chemistry 2006; 6: 1825
    • 132b Reith ME. A, Blough BE, Hong WC, Jones KT, Schmitt KC, Baumann MH, Partilla JS, Rothman RB, Katz JL. Drug and Alcohol Dependence 2015; 147: 1
  • 133 Fehler SK, Pratsch G, Heinrich MR. Angew. Chem. Int. Ed. 2014; 53: 11361