1,2,3-Benzothiadiazole 1,1-Dioxide1

[37150-27-9]  · C6H4N2O2S  · 1,2,3-Benzothiadiazole 1,1-Dioxide  · (MW 168.17)

(benzyne precursor1)

Solubility: sol ether.

Preparative Method: by diazotization of sodium 2-aminobenzenesulfinate, which is obtained in three steps from 2-nitroaniline.2

Handling, Storage, and Precautions: it can be isolated as yellow-brown needles, but slowly decomposes even at 0 °C and explodes between 45 and 60 °C. A safer alternative is to use it in solution, in which it decomposes smoothly at 10 °C. Preparation and handling should be carried out with good shielding.

Generation of Benzyne.1

Decomposition of 1,2,3-benzothiadiazole 1,1-dioxide in ether affords benzyne, nitrogen, and sulfur dioxide (eq 1).2

This is a very mild procedure (neutral, relatively low temperature) for the generation of benzyne. However, despite the examples which follow, the time-consuming preparation of 1,2,3-benzothiadiazole 1,1-dioxide has greatly limited its use in synthesis. Moderate yields have been obtained in the reactions of cyclic dienes with benzyne generated in situ from 1,2,3-benzothiadiazole 1,1-dioxide. Furan, for example, traps benzyne efficiently under these conditions to afford the adduct in 54% yield (eq 2).3

2-Pyrone reacts with benzyne to give a bicyclic adduct, which loses CO2 by a retro-Diels-Alder reaction to afford naphthalene in 36% yield (eq 3).3

Cyclopentadiene derivatives react with benzyne to yield bridged compounds (eq 4).4

Due to the low decomposition temperature of 1,2,3-benzothiadiazole 1,1-dioxide, cycloaddition with less reactive dienes affords complex mixtures with poor yields of cycloadducts. For example, the decomposition of 1,2,3-benzothiadiazole 1,1-dioxide in thiophene leads to a complex mixture with less than a 5% yield of products derived from cycloaddition.5

The effect of silver(I) on the course of the reactions of benzyne with polyenes has also been reported.6 When 1,2,3-benzothiadiazole 1,1-dioxide was decomposed in the presence of 1,3-cyclohexadiene, a complex mixture was obtained. Four products were characterized, giving a total yield of 28% (eq 5). When 1,2,3-benzothiadiazole 1,1-dioxide was added to a silver-diene complex, the yield and selectivity of the reaction were improved (eq 6).

Related Reagents.

Benzenediazonium-2-carboxylate; Diphenyliodonium Carboxylate.

1. Hoffmann, R. W. Dehydrobenzene and Cycloalkynes; Academic: New York, 1976.
2. Wittig, G.; Hoffmann, R. W. OS 1967, 47, 4.
3. Wittig, G.; Hoffmann, R. W. CB 1962, 95, 2718.
4. Wiesner, K.; Ho, P.-T.; Jain, R. C.; Lee, S. F.; Oida, S.; Philipp, A. CJC 1973, 51, 1448.
5. Del Mazza, D.; Reinecke, M. G. JOC 1988, 53, 5799.
6. Crews, P.; Beard, J. JOC 1973, 38, 529.

Luis Castedo & Enrique Guitián

CSIC & University of Santiago de Compostela, Spain

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