反应详情

Again, referring to Scheme I, modifying a procedure as described (E. Campaigne and John Ashby, J. Het. Chem. 517-521, August 1969 on page 521) dibenzothiophene 1 was treated with bromine in carbon disulfide to afford 2,8-dibromo-dibenzothiophene 2. Reaction of 2,8-dibromo-dibenzothiophene 2 with >90% nitric acid at 50-60° C. gave as the major product 2,8-dibromo-3,7-dinitrodibenzothiophene-5-oxide 3a. A mixture of 2,8-dibromo-3,7-dinitrodibenzothiophene-5-oxide 3a in 1:1 dimethylacetamide (DMAC)/dioxane was treated with copper (I) cyanide (Cu(I)CN) for about 10 hours at 50-150° C. followed by further treatment with ferric chloride/concentrated hydrochloric acid to yield as the major product 3,7-dinitrodibenzothiophene-2,8-dicarbonitrile 4a. Further treatment of 3,7-dinitrodibenzothiophene-2,8-dicarbonitrile 4a with glacial acetic acid, hydrobromic acid and water at 50-100° C. followed by treatment with sodium hydroxide at 50-100° C. for 0.5 to 3 hours followed by acidification to a pH of 1 to 5 affords as the major product 3,7-dinitrodibenzothiophen-2,8-dicarboxylic acid 5a. Reaction of 3,7-dinitrodibenzothiophene-2,8-dicarboxylic acid 5a with an excess of halogenating agent which include but are not limited to thionyl chloride, thionyl chloride in the presence of N,N-dimethylformamide (DMF), oxalyl chloride, selenium tetrafluoride, phosphorus trichloride, phosphorus tribromide or pentabromide and the like at reflux under anhydrous conditions in the presence of an anhydrous polar organic solvent which include but are not limited to p-dioxane, tetrahydrofuran, methyl alcohol, chloroform followed by further treatment with 1-100 equivalents of an alkylamine base, which include but are not limited to triethylamine, N,N-diethylmethylamine, N,N-diethylaniline, N,N-diethylethylenediamine, N,N-diisopropylethylamine, or pyridine and the like in an alcohol, R3OH, where R3 is straight chain alkyl of 1 to 5 carbon atoms, branched chain alkyl of 3 to 5 carbon atoms or benzyl which include but are not limited to methyl, ethyl, propyl, isopropyl, butyl or benzyl alcohol, stirred at a temperature range from 0-75° C. for about 1 to 100 hours to give as the major product 3,7-dinitrodibenzothiophene-2,8-dicarboxylic acid diester 6a where R3 is hereinbefore defined. A heterogeneous mixture containing major product 3,7-dinitrodibenzothiophene-2,8-dicarboxylic acid diester 6a was treated with a reducing agent which include but are not limited to powdered iron, tin(II) chloride, zinc metal or palladium on charcoal with hydrogen in alcoholic solvents which include but are not limited to methyl alcohol, ethyl alcohol, propyl alcohol or 2-methoxyethanol and the like and an organic acid which include but are not limited to acetic acid at a temperature range from 50-120° C. for about 2 hours or until completion as indicated by thin-layer chromatography (TLC). Chromatographic purification on silica gel affords 3,7-diaminodibenzothiophene-2,8-dicarboxylic acid diester 7 where R3 is hereinbefore defined and 3-amino-7-chlorodibenzothiophene-2,8-dicarboxylic acid diester 8 where R3 is hereinbefore defined.