· Benzyl p-Toluenesulfonate
· (MW 262.32)
(benzylating agent for heteroatomic functional groups and enolate anions)
Alternate Name: benzyl tosylate.
Physical Data: mp 58 °C.
Solubility: sol alcohols, ether, and aromatic solvents.
Preparative Method: typically prepared from tosyl chloride and benzyl alcohol.1
Handling, Storage, and Precautions: may be stored as a crude or purified solid at 0 °C for up to 3 months; potential vessicant. Use in a fume hood.
Benzylation of Heteroatomic Functional Groups.
Phenols are benzylated with this reagent under basic conditions. The regioselectivity, when more than one phenol is present in the substrate, favors the less sterically hindered hydroxy group (eq 1).2 In the case of phenols where C-alkylation commonly accompanies O-alkylation, benzyl tosylate gives higher selectivity for O-alkylation than Benzyl Chloride.2 This is illustrated in the benzylation of a phloroglucinol derivative, where benzyl chloride afforded only 18% of the desired product under similar reaction conditions (eq 2).
Lactams3 and vinylogous amides4 can be selectively N-benzylated under basic conditions with this reagent (eq 3). Methylamine affords benzylmethylamine when reacted in excess with benzyl tosylate in ether.5
- 1. (a) Tipson, R. S. JOC 1944, 9, 235. (b) Tipson, R. S. JOC 1947, 12, 133. (c) Kochi, J. K.; Hammond, G. S. JACS 1953, 75, 3443. (d) Blackwell, J.; Hickinbottom, W. J. JCS 1963, 366.
- 2. Dewick, P. M. SC 1981, 11, 853.
- 3. Davis, D. A.; Gribble, G. W. TL 1990, 31, 1081.
- 4. Dannhardt, G.; Paulus, B.; Ziereis, K. AP 1988, 561.
- 5. Anderson, W. K.; Veysoglu, T. S 1974, 665.
William E. Bauta
Sandoz Research Institute, East Hanover, NJ, USA
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