Synlett 2011(10): 1435-1438  
DOI: 10.1055/s-0030-1260760
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Direct Benzylic Oxidation with Sodium Hypochlorite Using a New Efficient Catalytic System: TEMPO/Co(OAc)2

Can Jin, Li Zhang, Weike Su*
Key Laboratory of Pharmaceutical Engineering of Ministry of Education, College of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou 310014, P. R. of China
Fax: +86(571)88320752; e-Mail: pharmlab@zjut.edu.cn;
Further Information

Publication History

Received 5 March 2011
Publication Date:
26 May 2011 (online)

Abstract

Direct benzylic oxidation of arenes was achieved using NaClO/TEMPO/Co(OAc)2. Various aromatic aldehydes and ketones were obtained from alkylarenes directly by benzylic oxidation in good to excellent yields. The reaction reactivity, selectivity, and scope of the reaction were investigated.

    References and Notes

  • 1a Sheldon RA. Kochi JK. Metal-Catalyzed Oxidations of Organic Compounds   Academic Press; New York: 1981. 
  • 1b Warren S. In Organic Synthesis: The Disconnection Approach   J. Wiley and Sons; Singapore: 2004.  p.57 
  • 1c Warren S. In Organic Synthesis: The Disconnection Approach   John Wiley and Sons; Singapore: 2004.  p.201 
  • 1d Warren S. In Organic Synthesis: The Disconnection Approach   John Wiley and Sons; Singapore: 2004.  p.330 
  • 1e Recupero F. Punta C. Chem. Rev.  2007,  107:  3800 
  • 1f Handbook of C-H Transformation   Dyker D. Wiley-VCH; Weinheim: 2005. 
  • 2a Rangarajan R. Eisenbraun EJ. J. Org. Chem.  1985,  50:  2435 
  • 2b Rathore R. Saxena N. Chandrasekaran S. Synth. Commun.  1986,  16:  1493 
  • 2c Muzart J. Tetrahedron Lett.  1987,  28:  3139 
  • 3a Gannon SM. Krause JG. Synthesis  1987,  915 
  • 3b Li WS. Liu LG. Synthesis  1989,  293 
  • 3c Zhao D. Lee DG. Synthesis  1994,  915 
  • 3d Shaabani A. Lee DG. Tetrahedron Lett.  2001,  42:  5833 
  • 4a Banik BK. Venkatraman MS. Mukhopadhyay C. Becker FF. Tetrahedron Lett.  1998,  39:  7247 
  • 4b Shaabani A. Bazgir A. Abdoli M. Synth. Commun.  2002,  32:  675 
  • 4c Shaabani A. Lee DG. Synth. Commun.  2003,  33:  1255 
  • 5a Ishii Y. Nakayama K. Takeno M. Sakaguchi S. Iwahama T. Nishiyama Y. J. Org. Chem.  1995,  60:  3934 
  • 5b Yang G. Zhang Q. Miao H. Tong X. Xu J. Org. Lett.  2005,  7:  263 
  • 6 Lee NH. Lee C. Jung DS. Tetrahedron Lett.  1998,  39:  1385 
  • 7 Dohi T. Takenaga N. Goto A. Fujioka H. Kita Y.
    J. Org. Chem.  2008,  73:  7365 
  • 8 Catino AJ. Nichols JM. Choi H. Gottipamula S. Doyle MP. Org. Lett.  2005,  7:  5167 
  • 9 Li H. Li Z. Shi Z. Tetrahedron  2009,  65:  1856 
  • 10 Yi CS. Kwon KH. Lee DW. Org. Lett.  2009,  11:  1567 
  • 11a Vogler T. Studer A. Synthesis  2008,  1979 
  • 11b Ciriminna R. Pagliaro M. Org. Process Res. Dev.  2010,  14:  245 
  • 12a Lucio Anelli PL. Biffi C. Montanari F. Quici S. J. Org. Chem.  1987,  52:  2559 
  • 12b Semmelhack MF. Schmid CR. Cortes DA. Chou CS. J. Am. Chem. Soc.  1984,  106:  3374 
  • 12c Shibuya M. Sato T. Tomizawa M. Iwabuchi Y. Chem. Commun.  2009,  13:  1739 
  • 12d Hirota M. Tamura N. Saito T. Isogai A. Carbohydr. Polym.  2009,  78:  330 
  • In fact, the amount of HClO becomes significant at the pH of 8.3:
  • 13a Montanari F. Penso M. Quici S. Vigano P. J. Org. Chem.  1985,  50:  4888 
  • 13b Banfi S. Montanari F. Quici S. J. Org. Chem.  1989,  54:  1850 
  • 14a Singh SJ. Jayaram RV. Catal. Commun.  2009,  10:  2004 
  • 14b Marwah P. Marwah A. Lardy HA. Green Chem.  2004,  6:  570 
  • TEMPO can react directly with activated hydrocarbons by hydrogen abstraction:
  • 15a Coseri S. Ingold KU. Org. Lett.  2004,  6:  1641 
  • 15b Babiarz JE. Cunkle GT. DeBellis AD. Eveland D. Pastor SD. Shum SP. J. Org. Chem.  2002,  67:  6831 
  • 16 For example, a similar mechanism is proposed: Auty K. Gilbert BC. Barry Thomas C. Brown SW. Jones CW. Sanderson WR. J. Mol. Catal. A: Chem.  1997,  117:  279 
  • It was suggested that the alkyl hypochlorite is converted to ketone in an E2-type reaction:
  • 18a Mohrig JR. Nienhulus DM. Linck CF. Zoeren CV. Fox BB. Mahaffy PG. J. Chem. Educ.  1985,  62:  519 
  • 18b Sakai A. Hendrickson DG. Hendrickson WH. Tetrahedron Lett.  2000,  41:  2759 
  • 18c Bright ZR. Luyeye CR. Marie Morton AS. Sedenko M. Landolt RG. Bronzi MJ. Bohovic KM. Alex Gonser MW. Lapainis TE. Hendrickson WH. J. Org. Chem.  2005,  70:  684 
  • It was reported that the oxidation of moderately active alkylaromatics based on NaOCl with a mechanism involving the substitution course:
  • 19a Correia J. J. Org. Chem.  1992,  57:  4555 
  • 19b Clark JH. Grigoropoulo G. Scott K. Synth. Commun.  2000,  30:  3731 
  • 21 Dailey JI. Hays RS. Lee H. Mitchell RM. Ries JJ. Landolt RG. Husmann HH. Lockridge JB. Hendrickson WH. J. Org. Chem.  2000,  65:  2568 
17

General Procedure for the Oxidation of 1a Using Ca(ClO) 2 To a mortar were added 1a (1 mmol), TEMPO (0.05 mmol), Co(OAc)2 (0.01 mmol), Ca(ClO)2 (2.5 mmol), and silica gel (0.3 g). After 0.5 h under solid grinding at r.t., the reaction was complete (TLC control). The reaction mixture was dissolved in CH2Cl2 (3 mL). After filtration, the solvent was evaporated off. The remaining mixture was passed through a silica gel column to give 2a. White solid; mp 47.8-49.4 ˚C. ¹H NMR (400 MHz, CDCl3): δ = 7.74-7.84 (m, 4 H), 7.53-7.63 (m, 2 H), 7.41-7.52 (m, 4 H). ¹³C NMR (100 MHz, CDCl3): δ = 196.7, 137.5, 132.3, 130.0, 128.2. MS (EI): m/z (%) = 182 (100) [M+], 105 (15), 77 (14), 51 (8).

20

General Procedures
To a solution of alkylarenes (1 mmol) in CH2Cl2 (3 mL) at 0-5 ˚C, TEMPO (0.05 mmol) and Co(OAc)2 (0.01 mmol) were added followed by the quick addition of a sample containing 3 mmol of aq NaClO at pH 8.3. After 6 h under magnetic stirring, the reaction was complete (TLC control). The organic phase is separated, washed with H2O, and dried over Na2SO4. After filtration, the solvent was evaporated off. The remaining mixture was passed through a silica gel column to obtain the pure products.
Compound 2o: pink solid; mp 160.9-162.1 ˚C. ¹H NMR (400 MHz, CDCl3): δ = 8.21 (d, J = 7.8 Hz, 2 H), 7.39-7.68 (m, 6 H), 2.13 (s, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 181.4, 169.9, 141.8, 140.6, 134.4, 133.1, 133.0, 131.5, 130.3, 130.0, 129.0, 128.6, 127.7, 126.3, 89.6, 23.6. MS (EI): m/z (%) = 323 (3) [M+ + 4], 321 (18) [M+ + 2], 319 (27) [M+], 284 (64), 242 (100), 213 (95), 178 (71). ESI-HRMS: m/z calcd for C16H12Cl2NO2: 320.0245; found: 320.0226.

22

Gramscale Preparation of 2a
To a solution of 1a (8.4 g,50 mmol) in CH2Cl2 (150 mL) at 0-5 ˚C, TEMPO (0.39 g, 2.5 mmol) and Co(OAc)2 (0.12 g, 0.5mmol) were added followed by the quick addition of a sample containing 150 mmol of aq NaClO at pH 8.3. The mixture was vigorously stirred for 6 h. The organic phase is separated and washed with H2O. The solvent was evaporated off. Purification of the residue by recrystallization gave 2a (7.98 g, 47.5 mmol, mp 47-49 ˚C) in 95% yield.