Synlett 2008(7): 1021-1026  
DOI: 10.1055/s-2008-1066997
LETTER
© Georg Thieme Verlag Stuttgart · New York

TiCl4/tert-Butyl Hydroperoxide: Chemioselective Oxidation of Secondary ­Alcohols and Suppression of Sharpless Epoxidation

Chun-Tin Shei, Hao-Lun Chien, Kuangsen Sung*
Department of Chemistry, National Cheng Kung University, Tainan 70101, Taiwan
Fax: +886(6)2740552; e-Mail: kssung@mail.ncku.edu.tw;
Further Information

Publication History

Received 25 December 2007
Publication Date:
17 March 2008 (online)

Abstract

Replacing Ti(Oi-Pr)4 with TiCl4 under the normal Sharpless epoxiation conditions resulted in a shut down of the epoxidation reaction. Instead, a chemioselective oxidation of secondary alcohols in the presence of primary alcohols occurred.

7

The general procedure for alcohol oxidation with TiCl4/TBHP or Ti(Oi-Pr)4/TBHP is shown as follows. To alcohol substrate 1 (1 mmol) and 4 Å MS (0.5 g) in CHCl3, CH2Cl2, or CDCl3 (2 mL) at r.t. was added TiCl4 or Ti(Oi-Pr)4 (0.1 mmol, 10% in CHCl3). The mixture was stirred at r.t. for 1 h. Toluene solution of TBHP (1.7 mmol) was added into the mixture, followed by stirring at r.t. or reflux conditions for 1 or 2 d. Low-boiling-point products 2c and 2d were purified by trap-to-trap fractionation and other products were purified by column chromatography with silica gel as stationary phase and hexane-EtOAc as mobile phase. All the products are known and their characterizations are shown as follows.
Compound trans -3a: [2d] 1H NMR (300 MHz, CDCl3): δ = 3.19 (m, 1 H), 3.78 (dd, J = 12.8, 3.5 Hz, 1 H), 3.92 (d, J = 2.1 Hz, 1 H), 4.05 (dd, J = 12.8, 2.1 Hz, 1 H), 7.30 (m, 5 H, Ph). 13C NMR (100 MHz, CDCl3): δ = 55.5, 61.2, 62.5, 125.6, 128.2, 128.4, 136.7.
Compound syn-3b: [9a] 1H NMR (300 MHz, CDCl3): δ = 1.31 (d, 3 H, J = 6.5 Hz), 3.09 (m, 1 H), 3.95 (d, 1 H, J = 2.1 Hz), 4.10 (m, 1 H), 7.32 (m, 5 H). 13C NMR (100 MHz, CDCl3): δ = 136.9, 128.5, 128.3, 125.7, 65.5, 64.8, 54.6, 18.7.
Compound anti-3b: [9a] 1H NMR (300 MHz, CDCl3): δ = 1.29 (d, 3 H, J = 6.4 Hz), 3.05 (m, 1 H), 3.86 (d, 1 H, J = 2.0 Hz), 3.85 (m, 1 H), 7.30 (m, 5 H). 13C NMR (100 MHz, CDCl3): δ = 136.7, 128.4, 128.2, 125.6, 67.1, 66.4, 56.5, 20.0.
Compound 2b: [9b] IR (CDCl3): 1678 cm-1; 1H NMR (300 MHz, CDCl3): δ = 2.40 (s, 3 H), 6.73 (d, J = 16.0 Hz, 1 H), 7.41 (m, 3 H), 7.51-7.57 (m, 3 H). 13C NMR (100 MHz, CDCl3) δ = 27.5, 127.2, 128.5, 129.1, 130.5, 134.7, 143.5, 198.2. 2c [9c] : IR (CDCl3): 1705 cm-1; 1H NMR (300 MHz, CDCl3): δ = 2.18 (s, 6 H). 13C NMR (100 MHz, CDCl3): δ = 208.1.
Compound 2d: [9d] IR (CDCl3): 1709 cm-1. 1H NMR (300 MHz, CDCl3): δ = 1.70 (m, 2 H), 1.83 (m, 4 H), 2.32 (m, 4 H). 13C NMR (100 MHz, CDCl3): δ = 25.1, 27.2, 42.2, 211.8.
Compound 2e: [9e] IR (CDCl3): 1695 cm-1. 1H NMR (300 MHz, CDCl3): δ = 1.23 (t, J = 7 Hz, 3 H), 2.98 (q, J = 7.0 Hz, 2 H), 7.40-7.58 (m, 3 H), 7.98 (m, 2 H). 13C NMR (100 MHz, CDCl3): δ = 8.1, 31.9, 127.7, 128.3, 132.8, 137.0, 200.8.
Compound 2g: [9f] IR (CDCl3): 1735, 1665 cm-1. 1H NMR (300 MHz, CDCl3): δ = 7.52 (m, 2 H), 7.70 (m, 1 H), 8.21 (m, 2 H), 10.87 (s, 1 H). 13C NMR (100 MHz, CDCl3): δ = 129.1, 131.3, 132.2, 136.3, 164.0, 185.2.
Compound 2h: [9g] IR (CDCl3): 1661 cm-1. 1H NMR (300 MHz, CDCl3): δ = 7.46 (m, 4 H), 7.58 (m, 2 H), 7.95 (m, 4 H). 13C NMR (100 MHz, CDCl3): δ = 129.2, 129.9, 133.2, 135.0, 194.7.
Compound 2i: [9h] IR (CDCl3): 1737, 1670 cm-1. 1H NMR (300 MHz, CDCl3): δ = 1.44 (t, J = 7.0 Hz, 3 H), 4.43 (q, J = 7.0 Hz, 2 H), 7.47 (m, 2 H), 7.52 (m, 1 H), 8.03 (m, 2 H). 13C NMR (100 MHz, CDCl3): δ = 14.1, 61.2, 129.3, 131.4, 132.3, 136.5, 163.9, 186.0.
Compound 2j: [9i] IR (CDCl3): 1666 cm-1. 1H NMR (300 MHz, CDCl3): δ = 0.98 (t, 3 H, J = 7.3 Hz), 1.40 (m, 2 H), 1.60 (m, 2 H), 3.36 (q, J = 7.3 Hz, 2 H), 7.50 (m, 2 H), 7.64 (m, 1 H), 8.35 (m, 2 H). 13C NMR (100 MHz, CDCl3): δ = 13.7, 20.1, 31.3, 39.2, 128.5, 131.2, 133.4, 134.3, 161.7, 187.9.
Compound 2k: [9j] IR (CDCl3): 1710 cm-1. 1H NMR (300 MHz, CDCl3): δ = 2.2 (s, 3 H), 2.7 (t, J = 5.5 Hz, 2 H), 3.8 (t, J = 5.5 Hz, 2 H). 13C NMR (100 MHz, CDCl3): δ = 30.3, 45.6, 61.1, 208.5.
Compound 2l: [9k] IR (CDCl3): 1706 cm-1. 1H NMR (300 MHz, CDCl3): δ = 1.20 (d, J = 5.8 Hz), 2.18 (s, 3 H), 2.58 (d, J = 5.8 Hz, 2 H), 4.22 (m, 1 H). 13C NMR (100 MHz, CDCl3): δ = 25.9, 30.6, 51.5, 63.8, 208.9.