Chlorination of Benzylic and Allylic Alcohols with Trimethylsilyl Chloride Enhanced by Natural Sodium Montmorillonite

Abstract

A new and practical method for the efficient chlorination of tertiary, secondary, and primary benzylic and allylic alcohols is described. The method is characterized by the formation of hydrogen chloride from trimethylsilyl chloride and trace water, the formation of a carbenium ion through the protonation of an alcohol and subsequent dehydration, and the chlorination of the carbenium ion. During the process, sodium ion-exchanged montmorillonite plays a crucial role in capturing the generated hydrogen chloride, stabilizing the carbenium intermediate as well as promoting the chlorination.

Key words

hydrous sodium montmorillonite - chlorination - benzylic alcohols - allylic alcohols - trimethylsilyl chloride

• References and Notes

• 1 For a list of chlorinating agents, see: Larock RC. Comprehensive Organic Transformations . Wiley-VCH; New York: 1999. 2nd ed., 689-697
• 2 Tertiary chlorides are easily prepared from tertiary alcohols using a concentrated HCl solution, while primary and secondary alcohols are slow to react with concentrated HCl. Thus an adequate catalyst is required.

The synthesis of chlorides from alcohols using gaseous hydrogen chloride:
• 3a Rule HG, Bain J. J. Chem. Soc. 1930; 1894
• 3b Denegri B, Streiter A, Juric S, Ofial AR, Kronja O, Mayr H. Chem. Eur. J. 2006; 12: 1648
• 4 For a review of SOCl₂, see: Pizey JS. Synthetic Reagents . Vol. 1. Wiley; New York: 1974: 321-357
• 5 For a review, see: Salomaa P, Kankaanpera A, Pihlaja K. In The Chemistry of the Hydroxyl Group . Patei S. Wiley; New York: 1971. Part 1, 595-622

Hydrogen chloride gas is not only commercially available, but can also be prepared in laboratories. For the laboratory-scale preparation of hydrogen chloride gas, see:
• 6a Maurya MR. J. Chem. Educ. 1990; 67: 974
• 6b Arnaiz FJ. J. Chem. Educ. 1995; 72: 1139
• 7 Wang J, Masui Y, Onaka M. Tetrahedron Lett. 2010; 51: 3300
• 8 Wang J, Masui Y, Onaka M. Synlett 2010; 2493
• 9 Wang J, Masui Y, Onaka M. ACS Catal. 2011; 1: 446
• 10 Tandiary MA, Masui Y, Onaka M. Tetrahedron Lett. 2014; 55: 4160
• 11 Synder DC. J. Org. Chem. 1995; 60: 2638
• 12a Le Roux C, Gaspard-Iloughmane H, Dubac J. J. Org. Chem. 1994; 59: 2238
• 12b Labrouillere M, Le Roux C, Gaspard-Iloughmane H, Dubac J. Synlett 1994; 723
• 13 Lee JG, Kang KK. J. Org. Chem. 1988; 53: 3634
• 14 Hydrous Na-Mont was obtained from Kunimine Industries, Japan, and contains 14 wt% H₂O.
• 15 A Representative Procedure for the Chlorination of 1a with TMSCl in the Presence of Na-Mont In a flask was placed Na-Mont (30 mg), 1a (1 mmol, 0.18 g), TMSCl (2 mmol, 0.22 g, 0.25 mL), and CH₂Cl₂ (5 mL). The mixture was stirred at r.t. for 40 min. The solid material was filtered off, and the filtrate was concentrated. Compound 3a was isolated by Kugelrohr distillation under vacuum in 90% yield as a colorless liquid. NMR Data of 3a ¹H NMR (500 MHz, CDCl₃): δ = 7.42–7.18 (m, 10 H), 6.08 (s, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 141.1, 128.6, 128.1, 127.8, 64.3.
• 16 H-Mont and Sn-Mont were prepared from Na-Mont by an ion exchange and contain 8 wt% and 18 wt% water, respectively. See Supporting Information.
• 17 Although a mixture of 3b and 4b was obtained after the reaction, 3b can be easily separated from the mixture by distillation due to the significant difference in boiling points of these two compounds. NMR Data of 3b ¹H NMR (500 MHz, CDCl₃): δ = 7.29 (s, 8 H), 6.03 (s, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 139.2, 134.3, 129.2, 128.9, 62.7.