1,2,3-benzothiadiazole

Another heterocyclic molecule that can serve as a benzyne precursor is benzothiadiazole-1,1-dioxide, which decomposes with elimination of sulfur dioxide and nitrogen. ... 

Another approach involves utilization of the amines for addition of a fused pyridine ring to the benzothiadiazole skeleton. The Gould-Jacobs reaction of 4-amino-2,l,3-benzothiadiazole 60 with diethyl ethoxymethylenemalonate gave the substitution product, and, after thermal cyclization in diphenyl ether, afforded the... 

Amino-2,l,3-benzothiadiazole treated under similar conditions afforded, re-gioselectively, an analogous angularly annelated ester 68 and acid 69, both to be tested for inhibition of the DNA synthesis (74MI1). Subsequent alkylation of the... 

Under similar conditions, as in the case of 5-amino-2,l,3-benzothiadiazole, and starting from 6-amino-l,2,3-benzothiadiazole 72, the l,2,3-thiadiazolo[5, 4-/ quinoline derivatives 73 resulted (Scheme 28) and were tested for antibacterial properties (74JAP(K)1). 

C. 1,2,3-Benzothiadiazole 1,1-dioxide. Caution 1,2,3-Benzo-thiadiazole 1,1-dioxide in the solid slate can explode spontaneously, particularly on being warmed, jolted, or scratched. For most purposes it need not be isolated, but can be used in solutions, which are relatively safe. Any operations involving the solid material should be done very carefully, using good shielding. 

Benzothiadiazole 1,1-dioxide slowly decomposes even at 0°, hence it should always be used on the day on which it is made. For most purposes it is not necessary to isolate the dioxide the ether solution can be used, or solutions in other solvents can be prepared by adding the other solvent and distilling off the ether under reduced pressure (bath temperature 0°). In this way larger amounts of the dioxide than are described in this procedure can be handled without danger. 

Benzothiadiazole 1,1-dioxide can be conveniently assayed and characterized without isolation by forming its adduct with cyclopentadiene.5 The following procedure illustrates characterization, for assay the same procedure can be applied to an aliquot, with all amounts scaled down in proportion. The dried ether extract of 1,2,3-benzothiadiazole 1,1-dioxide prepared from 1.43 g (0.0080 mole) of sodium 2-aminobenzene-sulfinate is concentrated to about 20 ml at 0°, and 20 ml. of acetonitrile at —20° is added. Twenty milliliters of cold, freshly prepared cyclopentadiene6 is added The mixture is kept overnight at —10° to 0°. Solvent and excess cyclopentadiene are removed by evaporation at 0° under reduced pressure to leave 1.20-1.28 g. (64-68% based on sodium 2-aminobenzenesulfinate) of crude 1-1 adduct, mp. 87° (dec.). For purification it is dissolved in 20 ml. of methylene chloride, 70 ml. of ether is added, and the solution is kept at —70°. Adduct decomposing at 90° crystallizes recovery is about 75%. From pure, crystalline 1, 2, 3-benzothiadiazole 1,1-dioxide the yield of adduct is 92-98%. 

Purer product can be obtained by reducing 1,2,3-benzothiadiazole 1,1-dioxide with zinc and acetic acid to 1,2,3-benzo-thiadiazoline 1,1-dioxide, which is oxidized back with lead tetraacetate.5... 

Benzothiadiazole 1,1-dioxide has been prepared only by the present method.5... 

Benzothiadiazole 1,1-dioxide decomposes smoothly in solution at 10° to give dehydrobenzene ( benzyne ), nitrogen, and sulfur dioxide.5,7 In this way, as well as by the thermal... 

Addition, acetic acid to bicyclo[2.2.1]-hepta-2,5-diene to give nortri-cyclyl acetate, 46, 74 1,2,3-benzothiadiazole 1,1-dioxide to cyclopentadiene, 47, 8 benzyne to tetraphenylcyclopentadie-none, 46,107 Br, F to 1-heptene, 46,10 carbon tetrachloride to olefins, 46, 106... 

Benzophenone 46, 36 solvent for Diels Alder reactions at elevated temperatures, 46, 44 1,2,3 Benzothiadiazole 1,1 dioxide, 47,4... 

Cyclooctanone, condensation with diethyl carbonate, 47, 20 Cyclopentadiene, adduct formation with 1,2,3-benzothiadiazole 1,1-diox-ide, 47, 8... 

Compounds of special interest whose preparation is described include 1,2,3-benzothiadiazole 1,1-dioxide (a benzyne precursor under exceptionally mild conditions), bis(l,3-diphenylimida-zolidinylidene-2) (whose chemistry is quite remarkable), 6- di-melhylamino)julvene (a useful intermediate for fused-ring non-benzenoid aromatic compounds), dipkenylcyclopropenone (the synthesis of which is a milestone in theoretical organic chemistry), ketene di(2-melhoxyethyl) acetal (the easiest ketene acetal to prepare), 2-methylcyclopenlane-l,3-dione (a useful intermediate in steroid synthesis), and 2-phenyl-5-oxazolone (an important intermediate in amino acid chemistry). 

Benzopentathiepin (3, R1 =R2 = H) is produced in 54% yield from 1,2,3-benzothiadiazole and sulfur402 and in 97% yield from 1,3-benzodithiole-2-thione and sulfur in liquid ammonia in the presence of 1,3-dinitrobcnzcnc.403 These methods have also been used for the preparation of various substituted benzopentathiepins 3. 

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