How Electrophilic Are Keteniminium Ions?

Dedication

Dedicated to our friend and colleague Paul Knochel on the occasion of his 70th birthday.

Abstract

Keteniminium triflates (R₂C=C=NMe₂ ⁺ TfO⁻) react via classical electrophilic aromatic substitutions with electron-rich arenes forming Wheland intermediates that rapidly undergo triflate-catalyzed tautomerizations to enammonium ions. These ions do not isomerize to the thermodynamically more-stable iminium ions and can quantitatively be converted into the corresponding enamines by treatment with triethylamine. Kinetic studies of keteniminium attack at the arenes provided the electrophilicity parameters of the keteniminium ions E = −2.8 (for R = Me) and E = −1.9 (for R = Ph). These values quantify the one-bond electrophilic reactivity of keteniminium ions and allow us to derive the energy of concert of their [2 + 2]-cycloadditions with alkenes.

Keywords

Kinetics - Linear free energy relationships - Quantum-chemical calculations - Reaction mechanism - Acylation

Publication History

Received: 05 June 2025

Accepted after revision: 04 July 2025

Article published online:
13 August 2025

• References

• 1a Marchand-Brynaert J, Ghosez L. J Am Chem Soc 1972; 94: 2870
• 1b Sidani A, Marchand-Brynaert J, Ghosez L. Angew Chem Int Ed 1974; 13: 267
• 1c Viehe HG, Buijle R, Fuks R, Merényi R, Oth JMF. Angew Chem Int Ed 1967; 6: 77

Reviews:
• 2a Ghosez L, Marchand-Brynaert J. Iminium Salts in Organic Chemistry, Part I. In Advances in Organic Chemistry Vol. 9. Böhme H, Viehe HG. (eds.) New York: Wiley; 1976: 421
• 2b Snider BB. Chem Rev 1988; 88: 793
• 2c Zificsak CA, Mulder JA, Hsung RP, Rameshkumar C, Wei L-L. Tetrahedron 2001; 57: 7575
• 2d Madelaine C, Valerio V, Maulide N. Chem Asian J 2011; 6: 2224
• 2e Evano G, Lecomte M, Thilmany P, Theunissen C. Synthesis 2017; 49: 3183
• 2f Ghosez L. Tetrahedron 2019; 75: 130345
• 2g Chen Y-B, Qian P-C, Ye L-W. Chem Soc Rev 2020; 49: 8897
• 2h Maskeri MA, Fernandes AJ, Di Mauro G, Maulide N, Houk KN. J Am Chem Soc 2022; 144: 23358
• 2i Prysiazhniuk K, Polishchuk O, Shulha S. et al. Chem Sci 2024; 15: 3249
• 3a Mayr H, Kempf B, Ofial AR. Acc Chem Res 2003; 36: 66
• 3b Streidl N, Denegri B, Kronja O, Mayr H. Acc Chem Res 2010; 43: 1537
• 3c Mayr H, Ofial AR. Acc Chem Res 2016; 49: 952
• 4a Mayr H, Patz M. Angew Chem Int Ed 1994; 33: 938
• 4b Mayr H, Bug T, Gotta MF. et al. J Am Chem Soc 2001; 123: 9500
• 4c Lucius R, Loos R, Mayr H. Angew Chem Int Ed 2002; 41: 91
• 4d Mayr H, Ofial AR. Pure Appl Chem 1807; 2005: 77
• 4e Mayr H, Ofial AR. J Phys Org Chem 2008; 21: 584
• 4f Ammer J, Nolte C, Mayr H. J Am Chem Soc 2012; 134: 13902
• 4g Mayr H, Ofial AR. SAR QSAR Environ Res 2015; 26: 619
• 4h A frequently updated database of reactivity parameters N, s _N, and E (incl. references to the original publications) is freely accessible at: https://www.cup.lmu.de/oc/mayr/reaktionsdatenbank2/ (accessed at 21/05/2025)
• 5a Mayr H, Ofial AR, Sauer J, Schmied B. Eur J Org Chem 2000; 2000: 2013
• 5b Fichtner C, Mayr H. J Chem Soc Perkin Trans 2 2002; 1441
• 5c Li L, Mayer RJ, Ofial AR, Mayr H. J Am Chem Soc 2023; 145: 7416
• 5d Li L, Mayer RJ, Ofial AR, Mayr H. Pure Appl Chem. 2025 online ( )
• 6a Ghosez L, Haveaux B, Viehe HG. Angew Chem, Int Ed 1969; 8: 454
• 6b Falmagne J-B, Escudero J, Taleb-Sahraoui S, Ghosez L. Angew Chem, Int Ed 1981; 20: 879
• 6c Lambrecht J, Zsolnai L, Huttner G, Jochims JC. Chem Ber 1982; 115: 172
• 6d Bauer H, Kühlein K. In Methoden Org Chem (Houben-Weyl). 4th ed. Vol E5. ; 1985: 1245

Heine, H. G. unpublished protocol, 1984; explicitly described in
• 7a Heine HG. In Methoden Org Chem (Houben-Weyl) 4th ed., Vol E15 1985; 1648
• 7b Ghosez L, George-Koch I, Patiny L. et al. Tetrahedron 1998; 54: 9207
• 8 Marchand-Brynaert J, Ghosez L. J Am Chem Soc 1972; 94: 2869
• 9 Matsushita H, Tsujino Y, Noguchi S, Yoshikawa S. Bull Chem Soc Jpn 1977; 50: 1513
• 10 Mayr H, Schneider R, Schade C, Bartl J, Bederke R. J Am Chem Soc 1990; 112: 4446
• 11 Horn M, Schappele LH, Lang-Wittkowski G, Mayr H, Ofial AR. Chem Eur J 2013; 19: 249
• 12a Marenich AV, Cramer CJ, Truhlar DG. J Phys Chem B 2009; 113: 6378
• 12b Chai J-D, Head-Gordon M. Phys Chem Chem Phys 2008; 10: 6615
• 12c Weigend F, Ahlrichs R. Phys Chem Chem Phys 2005; 7: 3297
• 12d All calculations were performed using Gaussian 16; see the Supporting Information for the full reference
• 13 Zhang P, Yu Z-X. J Org Chem 2024; 89: 4326
• 14 Li Z, Mayer RJ, Ofial AR, Mayr H. J Am Chem Soc 2020; 142: 8383
• 15 Appel R, Chelli S, Tokuyasu T, Troshin K, Mayr H. J Am Chem Soc 2013; 135: 6579
• 16 Böttger GM, Fröhlich R, Würthwein E-U. Eur J Org Chem 2000; 2000: 1589
• 17a Hyatt JA, Raynolds PW. Org React 1994; 45: 1559
• 17b Tidwell TT. Ketenes II. Hoboken (NJ): Wiley; 2006
• 17c Tidwell TT. Acc Chem Res 1990; 23: 273
• 17d Tidwell TT. Eur J Org Chem 2006; 2006: 563
• 18 Otto P, Feiler LA, Huisgen R. Angew Chem Int Ed 1968; 7: 737
• 19 Huisgen R, Feiler LA, Otto P. Chem Ber 1969; 102: 3444
• 20 Handke I, Schaumann E, Ketcham R. J Org Chem 1988; 53: 5298
• 21 Hachiya I, Moriwaki M, Kobayashi S. Bull Chem Soc Jpn 1995; 68: 2053
• 22 Gao J, He X-C, Liu Y-L. et al. Org Lett 2023; 25: 8824
• 23 Amer MI, Booth BL, Noori GFM, Proença MFJRP. J Chem Soc, Perkin Trans 1 1983; 1075
• 24 Bureau R, Mortier J, Joucla M. Bull Soc Chim Fr 1993; 130: 584
• 25 McGarrity JF, Prodolliet J, Smyth T. Org Magn Res 1981; 17: 59
• 26 Ingold CK, Shaw FR. J Chem Soc 1949; 575
• 27 Mayr H, Pock R. Chem Ber 1986; 119: 2473