Photograph

John Warkentin

Professor Emeritus

B.Sc., M.Sc. (Manitoba), Ph.D. (Iowa State), F.C.I.C.

Reactive Intermediates in Organic Chemistry
Mechanism and Synthetic Applications

Contact Information

    Our recent work has been concentrated around the chemistry of carbenes, such as alkoxyamino-, dialkoxy-, alkoxyaryloxy-, diaryloxy- and dialkylcarbenes. In all cases we have generated them from oxadiazoline precursors, by thermolysis or photolysis in solution, as depicted in Scheme 1, below.

scheme1.gif

Scheme 1

The thermal process lends itself well to syntheses with nucleophilic carbenes and the photo process is suitable for kinetics, by means of laser flash photolysis (LFP) techniques. It is also possible to study the kinetics of cation reactions in solution, by photolyzing (LFP) in acidic media, which protonate the diazoalkane to generate the short-lived diazonium ion and subsequently the carbocation. Most recently, we have found that allyloxy(methoxy)-, benzyloxy(methoxy)-, and dibenzyloxycarbenes undergo fast fragmentation in solution to radical pairs. That process is also being studied by means of computation, on model systems.

     Examples of reactions of nucleophilic carbenes, including insertions into CO-O bonds as well as C-C bonds, aromatic substitution , and some kinetic studies of electrophilic carbenes and carbocations, are in the publications listed below.

     The current Warkentin group, shown in the photograph below, consists of four PhD candidates: Xiaosong Lu, Nadine Merkley, Darren Reid, and Paul Venneri. Dr. Warkentin is now Professor Emeritus and is not taking new students.

group_image.gif

Front L-R: Nadine Merkley, Paul Venneri, John Warkentin, Darren Reid
Back: Xiaosong Lu

Selected Publications:

  1. J. A. Dunn, J. P. Pezacki, M. J. McGlinchey, and J. Warkentin. Reactions of Dimethoxycarbene with Cyclic Perchlorinated Olefins and Ketones. J.Org.Chem. 64:4344-4352, 1999.
  2. X. Lu and J. Warkentin. Ipso Aromatic Substitution from Reaction of a Carbene with DMAD. Tetrahedron Lett. 40:1483-1486, 1999.
  3. J. P. Pezacki, P. Couture, J. A. Dunn, J. Warkentin, P. Wood, J. Lusztyk, T. Chen, F. Ford, J. Toscano, and M. S. Platz. Rates of 1,2-Hydrogen Migration in Cyclohexylidene and Substituted Cyclohexylidenes. J.Org.Chem. 64:4456-4464, 1999.
  4. J. P. Pezacki, D. Shukla, J. Lusztyk, and J. Warkentin. Lifetimes of Dialkylcarbocations and Alkanediazonium Ions in Solution:Cyclohexadienyl Cations as Kinetic Probes for Cation Reactivity. J.Am.Chem.Soc. 121:6589-6598, 1999.
  5. E. L Tae, Z. Zhu, M. S. Platz, J. P. Pezacki, and J. Warkentin. Chemistry and Kinetics of Dipropylcarbene in Solution. J.Phys.Chem. 103:5336-5342, 1999.
  6. P. Couture and J. Warkentin. Synthesis of a Benzo-fused Oxapenem. Can.J.Chem. 76:241-244, 1998.
  7. H. M. Muchall, N. H. Werstiuk, B. Choudury, J. Ma, J. Warkentin, and J. P. Pezacki. Thermolysis of 2,2-Dimethoxy-5,5-dimethyl-D 3-1,3,4-oxadiazoline Studied with Photoelectron Spectroscopy. He(I) Photoelectron Spectrum of Dimethoxycarbene. Can.J.Chem. 76:238-241, 1998.
  8. J. P. Pezacki, J. Warkentin, P. D. Wood, J. Lusztyk, T. Yusawa, A. Gudmundsdöttir, S. Morgan, and M. S. Platz. Laser Flash Photolysis of 2-Adamantane-2,3'-[3H]-diazirine: a Reinvestigation. J.Photochem.Photobiol.A:Chem. 116:1-7, 1998.
  9. J. P. Pezacki, P. D. Wood, T. A. Gadosy, J. Lusztyk, and J. Warkentin. Laser Flash Photolysis studies of Oxygen and Sulfur Atom Transfer Reactions from Oxiranes and Thiiranes to Singlet Carbenes. J.Am.Chem.Soc. 120:8681-8691, 1998.
  10. P. C. Venneri and J. Warkentin. Homolysis of Carbenes. Free Radicals from Dialkoxycarbenes. J.Am.Chem.Soc. 120:11182-11183, 1998.
  11. J. Warkentin. Intra- and Intermolecular Reactions of Nucleophilic Carbenes. Macromol.Symp. 134:167-176, 1998.
  12. J. Warkentin. Diamino-, Amino(oxy)-, Dioxy-, Amino(thio)-, Oxy(thio)-, and Dithiocarbenes. Advances in Carbene Chemistry. U. H. Brinker. Ed. Greenwich,Ct.:JAI Press Inc. (2):245-295, 1998. 1-55983-837-4.
  13. J. F. Britten, K. Kassam, and J. Warkentin. A Novel Tricyclic Cyclobutanone Ketal. Acta Crystallographica C. C53:243-245, 1997.
  14. P. Couture, D. L. Pole, and J. Warkentin. Reactions of Nucleophilic Carbenes with Enols. J.Chem.Soc.,Perkin Trans.2:1565-1570, 1997.
  15. P. Couture and J. Warkentin. Spiro-fused 2-Alkoxy-2-amino-D3-1,3,4-oxadiazolines. Synthesis and Thermolysis to Corresponding Aminooxycarbenes. Can.J.Chem. 75:1264-1280, 1997.
  16. P. Couture and J. Warkentin. Chemistry of Cyclic Aminooxycarbenes. Can.J.Chem. 75:1281-1294, 1997.
  17. P. Couture, M. El-Saidi, and J. Warkentin. Ketene Acetals from Thermolysis of aryloxymethoxy Oxadiazolines. Evidence for Carbonyl Ylide Intermediates. Can.J.Chem. 75:326-332, 1997.
  18. K. Kassam and J. Warkentin. Reactions of Dialkoxycarbenes with Tethered Triple Bonds. Synthesis of Novel Heterocyclic Compounds. Can.J.Chem. 75:120-128, 1997.
  19. K. Kassam, P. Venneri, and J. Warkentin. Reactions of Alkoxyaryloxycarbenes with Tethered Triple Bonds. A New Synthesis of Substituted Benzofurans. Can.J.Chem. 75:1256-1263, 1997.
  20. J. P. Pezacki, D. L. Pole, J. Warkentin, T. Chen, F. Ford, J. Toscano, J. Fell, and M. S. Platz. Laser Flash and Dual Wavelength Photolysis of 3,4-Diaza-2,2-dimethoxy-1-oxa[4,3]spirooct-3-ene. Migration of Hydrogen and Carbon in Cyclobutylidene and in the Excited State of its Precursor. J.Am.Chem.Soc. 119:3191-3192, 1997.
  21. J. P. Pezacki, B. D. Wagner, C. S. Q. Lew, J. Warkentin, and J. Lusztyk. D3-1,3,4-Oxadiazolines: Photochemical Precursors to Sec-Alkanediazonium Ions in Acidic Solution. J.Am.Chem.Soc. 119:1789-1790, 1997.
  22. D. L. Pole and J. Warkentin. Formation and Rearrangement of a 2,2-Dimethoxyoxirane from Dimethoxycarbene and Fluorenone. J.Org.Chem. 62:4065-4067, 1997.
  23. J. P. Ross, P. Couture, and J. Warkentin. Nucleophilic Aromatic Substitution With Dialkoxycarbenes. Can.J.Chem. 75:1331-1335, 1997.
  24. J. Warkentin and J. McR. Woollard. Photolysis of 5,5-Dibenzyl-d3-1,3,4-oxadiazolines. Can.J.Chem. 75:289-307, 1997.

Contact Information

Mailing Address:
Dr J. Warkentin
Department of Chemistry
McMaster University
Hamilton, Ont., Canada
L8S 4M1		 Telephone:
Voice (905) 525-9140, ext. 23478
FAX   (905) 522-2509
Office: ABB-419
Laboratory: ABB-358 		E-mail: warkent@mcmaster.ca

Chemistry Faculty
Department of Chemistry.

30nov1999; jw