· (MW 237.05)
(brominating agent;1-4 transfer alkylating agent;1 used to synthesize 1,2-diketones5)
Physical Data: colorless crystalline solid, mp 86 °C.
Solubility: commonly used in THF solution.
Preparative Methods: by treating a chloroform solution of 2,2,5-trimethyl-1,3-dioxane-4,6-dione6 with Bromine and anhydrous Sodium Fluoride.
Purification: recrystallization from 2-propanol.
Handling, Storage, and Precautions: good laboratory practice should be sufficient when handling this reagent. The reagent is a relatively stable brominating agent and no special measures are required for its storage.
Addition of the anion of 3,3-dimethylthietane 1,1-dioxide (1) to a THF solution of the title reagent (2) afforded the bromo sulfone in good yield (eq 1).2 Alternative reagents such as Bromine, N-Bromosuccinimide, and 1-Chlorobenzotriazole did not effect the required transformation. Similarly, deprotonation of keto ester (3) and treatment with (2) afforded a-bromo ketone (4) stereoselectively. The addition of norbornene improved the efficiency of the reaction (eq 2).3 Treatment of azlactone (5) with (2) in the presence of Potassium Carbonate afforded the corresponding unsaturated azlactone via bromination and concomitant dehydrobromination. Reagents such as bromine, Sulfuryl Chloride, NBS, 2-Pyrrolidone Hydrotribromide, 1,3-Dibromo-5,5-dimethylhydantoin, and
1-chlorobenzotriazole were, however, more effective for this transformation (eq 3).4
Deprotonation of methyl 3-(methoxycarbonyl)-3,5-heptadienoate (6) with LDA in THF solution and treatment with (2) resulted in a-bromination and precipitation of the corresponding lithium salt of (2). Subsequent introduction of HMPA effected dissolution of this salt and resulted in SN2´´ alkylation. The product of this reaction can be smoothly hydrolyzed and subsequently decarboxylated (eq 4).1,2
Treatment of (2) with potassium acetate and subsequent pyrolysis has afforded butane-2,3-dione (eq 5).5
- 1. (a) Melvin, L. S., Jr.; Trost, B. M. JACS 1972, 94, 1790. (b) Trost, B. M.; Melvin, L. S., Jr. JACS 1976, 98, 1204.
- 2. Marino, J. P. CC 1973, 861.
- 3. Vedejs, E.; Wilber, W. R.; Twieg, R. JOC 1977, 42, 401.
- 4. Lott, R. S.; Breitholle, E. G.; Stammer, C. H. JOC 1980, 45, 1151.
- 5. Brown, R. F. C.; Eastwood, F. W.; Lim, S. T.; McMullen, G. L. AJC 1976, 29, 1705.
- 6. Pihlaja, K.; Seilo, M. ACS 1968, 22, 3053.
Peter D. Wilson
The Ohio State University, Columbus, OH, USA
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