3-Benzyl-4-methyl-1,3-thiazolium Chloride1

[4209-18-1]  · C11H12ClNS  · 3-Benzyl-4-methyl-1,3-thiazolium Chloride  · (MW 225.74)

(benzoin condensation catalyst; in the presence of bases, catalyzes the preparation of cyclic acyloins from dialdehydes, and of aromatic esters from aromatic aldehydes)

Physical Data: mp 188 °C; monohydrate 136 °C.2

Solubility: sol H2O, MeOH, EtOH and related solvents; insol ether or pentane.

Analysis of Reagent Purity: 1H NMR, mp.

Preparative Methods: colorless crystals prepared from 4-methyl-1,3-thiazole and benzyl chloride, or benzylthioformamide and chloroacetone.2

Handling, Storage, and Precautions: store dry.

Formation of Benzoins and Acyloins from Aldehydes.

Many thiazolium salts catalyze the formation of benzoins from aromatic aldehydes and of acyloins from aliphatic aldehydes, both in presence of bases (eq 1). This catalytic reaction has long been known,3 the most prominent salt being thiamine (vitamin B1). For details on the use of other salts, see 3-Benzyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium Chloride. The title reagent is the only one known to catalyze the formation of five- and six-membered cyclic acyloins in the presence of a base (eq 2).4

Oxidative Reactions.

Aromatic aldehydes in presence of a nitro compound, an alcohol, and a base react in a different way (eq 3). No formation of benzoins is observed, with only the carboxylic esters and nitrobenzene reduction products being formed.5 Quinones react analogously to nitro compounds.6 A test for the catalytic activity of azolium salts uses flavin as oxidant and indicator;7a details are given in a related bioorganic model study on the reaction of thiamine.7b

Addition of Aldehydes to Electrophilic Double Bonds.8

Full details are given under the entry for 3-Benzyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium Chloride. The reagent in the presence of bases catalyzes addition, but shows a tendency to form byproducts (eq 4). In this case the byproduct results from Michael addition to the benzoin instead of to the activated aldehyde.9

Reduction and Hydrolysis of the Reagent.

The reagent, like other thiazolium salts, is easily reduced by Sodium Borohydride10 to the thiazoline and the ring is easily cleaved by aqueous bases.2b

Other Reagents.

Acyloins are produced by the action of metals such as sodium on carboxylic esters;11 benzoins are produced by the catalytic action of cyanides on aromatic aldehydes.12

Related Reagents.

3-Benzyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium Chloride; 3-Benzylthiazolium Bromide.

1. (a) Fieser L. F.; Fieser M. FF 1979, 7, 18. (b) Beilstein 1983, 27-III/IV, 971.
2. (a) Karimullah JCS 1937, 961. (b) Sykes P.; Todd A. R. JCS 1951, 534.
3. Breslow R. JACS 1958, 80, 3719.
4. Cookson, R. C; Lane R. M. CC 1976, 804.
5. (a) Castells J.; Llitjós H.; Moreno-Mañas M. TL 1977, 205. (b) Castells J.; Pujol F.; Llitjós H.; Morena-Mañas M. T 1982, 38, 337. (c) Inoue H.; Higashiura CC 1980, 549. (d) Shinkai S.; Yamashita T.; Kusano Y.; Manabe O. JOC 1980, 45, 4947.
6. Vovk A. I.; Murav'eva I. V.; Yasnikov A. A. ZOB 1985, 55, 1400 (CA 1985, 103, 214 513p).
7. (a) Yano Y.; Tsukagoshi Y. JCR(S) 1984, 406. (b) Rastetter W. H.; Adams J. JOC 1981, 46, 1882.
8. Stetter H.; Kuhlmann H. OR 1991, 40, 407.
9. Castells J.; Duñach E.; Geijo F.; López-Calahorra F.; Prats M.; Sanahuja O.; Villanova L. TL 1980, 21, 2291.
10. Clarke G. M.; Sykes P. JCS(C) 1967, 1269.
11. (a) McElvain S. M. OR 1948, 4, 256. (b) Bloomfield J. J.; Owsley D. C.; Nelke J. M. OR 1976, 23, 259. (c) Finley K. T. CRV 1964, 64, 573. (d) Rühlmann K. S 1971, 236.
12. Ide W. S.; Buck J. S. OR 1948, 4, 269.

Heinrich Kuhlmann

RWTH, Aachen, Germany

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