Synlett 2013; 24(10): 1283-1285
DOI: 10.1055/s-0033-1338937
letter
© Georg Thieme Verlag Stuttgart · New York

Cobalt–Catalyzed Oxidative α-Cyanation of Tertiary Aromatic Amines with Trimethylsilyl Cyanide and tert-Butyl Hydroperoxide

Norio Sakai*
Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science (RIKADAI), Noda, Chiba 278-8510, Japan   Fax: +81(4)71239890   eMail: sakachem@rs.noda.tus.ac.jp
,
Akihiro Mutsuro
Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science (RIKADAI), Noda, Chiba 278-8510, Japan   Fax: +81(4)71239890   eMail: sakachem@rs.noda.tus.ac.jp
,
Reiko Ikeda
Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science (RIKADAI), Noda, Chiba 278-8510, Japan   Fax: +81(4)71239890   eMail: sakachem@rs.noda.tus.ac.jp
,
Takeo Konakahara
Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science (RIKADAI), Noda, Chiba 278-8510, Japan   Fax: +81(4)71239890   eMail: sakachem@rs.noda.tus.ac.jp
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Publikationsverlauf

Received: 06. März 2013

Accepted after revision: 16. April 2013

Publikationsdatum:
08. Mai 2013 (online)


Abstract

In this Letter is described that a cobalt(II)–tert-butyl hydroperoxide oxidizing system was used to catalyze the α-cyanation of aromatic tertiary amines in the presence of trimethylsilyl cyanide to produce the corresponding α-aminonitriles in good yields.

 
  • References and Notes

  • 7 Alagiri K, Prabhu KR. Org. Biomol. Chem. 2012; 10: 835
  • 8 Rueping M, Zhu S, Koenigs RM. Chem. Commun. 2011; 47: 12709 ; and references cited therein
  • 10 Murahashi S.-i, Komiya N. EP 1174419A1, 2002 ; Chem. Abstr. 2002, 136, 118063.
  • 11 During this study, Doyle and co-workers reported that a Co(OAc)2-TBHP oxidizing system undertook an oxidative Mannich-type reaction through a single electron transfer, see: Ratnikov MO, Doyle MP. J. Am. Chem. Soc. 2013; 135: 1549
  • 12 General Procedure To a 5 mL screw vial containing freshly distilled MeOH (0.6 mL) were successively added 1.0 M CoCl2 in a MeOH solution (6.0 μL, 0.0060 mmol), aromatic tertiary amine (0.60 mmol), TMSCN (188 μL, 2.50 mmol), and 5.5 M TBHP in decane solution (164 μL, 0.900 mmol) under an ambient atmosphere. The resultant mixture was stirred at 60 °C (bath temperature), and consumption of the starting amine was monitored by GC analysis. After the reaction the resultant mixture was quenched with a aqueous solution of Na2CO3. The aqueous layer was extracted with CH2Cl2, then the organic phases were dried over anhyd Na2SO4, filtered, and evaporated under a reduced pressure. The crude product was purified by silica chromatography (hexane–EtOAc, 4:1) to give the corresponding α-aminonitrile. Selected Data for the Prepared Aminonitriles N-Methyl-N-(4-methylphenyl)aminoacetonitrile (1) 1H NMR (500 MHz, CDCl3): δ = 2.28 (s, 3 H), 2.95 (s, 3 H), 4.12 (s, 2 H), 6.78 (d, 2 H, J = 9.0 Hz), 7.11 (d, 2 H, J = 9.0 Hz). 13C NMR (125 MHz, CDCl3): δ = 20.3, 39.4, 42.8, 115.3, 115.4, 129.8, 129.9, 145.6. MS (EI): m/z (%) = 160 (100) [M+]. N-Methyl-N-(4-bromophenyl)aminoacetonitrile (7) 1H NMR (500 MHz, CDCl3): δ = 2.99 (s, 3 H), 4.15 (s, 2 H), 6.72 (d, 2 H, J = 9.0 Hz), 7.38 (d, 2 H, J = 9.0 Hz). 13C NMR (125 MHz, CDCl3): δ = 39.3, 42.1, 112.5, 115.1, 116.4, 132.2, 146.7. MS (EI): m/z (%) = 224 (100) [M+]. The characterization of other α-aminonitriles was confirmed by 1H NMR and 13C NMR spectroscopic analysis.
  • 14 One reviewer pointed out that a reaction of CoCl2 with TBHP initially generated Co(III)Cl2(OH) and a tert-butyloxy radical (t-BuO, Equation 1, a). Those species are acceptable. However, both species would be promptly oxidized by an excess amount of TBHP to finally produce a tert-butylperoxy radical (t-BuOO) through the following plausible oxidation steps (Equation 1, b and c). Also, several groups reported that ruthenium-, rhodium-, or copper-catalyzed oxidative substitution of amines with TBHP, producing not the N,O-aminal derivative, but the amino peroxide derivative.4f,13b,15 Moreover, Doyle et al. showed that Co(OAc)2 converted TBHP into the tert-butylperoxy radical.11 Therefore, we proposed the initial formation of the tert-butylperoxy radical by CoCl2 as the plausible reaction path.
  • 15 Catino AJ, Nichols JM, Nettles BJ, Doyle MP. J. Am. Chem. Soc. 2006; 128: 5648