Action of Potassium Fluoride on 5-Benzensulfonyl-5,10-dihydro-10-trimethylsilylindole. Attempted Synthesis of Dibenzoazapentalene

Article abstract of DOI:10.1007/BF00808753

Mild and neutral experimental conditions were employed in order to maximize the chance of success in the isolation of dibenzoazapentalene (3), a compound expected to exhibit antiaromatic character, from a precursor.Thus, 5-benzensulfonyl-5,10-dihydro-10-trimethylsilylindeno<1,2-b>indole (7) was allowed to react with potassium fluoride at room temperature.The outcome of the reaction was complex, but the major product was identified as 5,5',10,10'-tetrahydro-10,10'-biindeno<1,2-b>indolylidene (15).Apparently, the anion 8 that was generated by the action of potassium fluoride on 7, did not suffer direct elimination of the benzensulfenate anion.Instead, presumably due to the antiaromaticity of 3, the benzenesulfenate anion was eliminated only after a series of electron transfer reactions, resulting in 15.Also, unexpectedly, dibenzoazapentalene dianion (5) was silylated exclusively at the 10-carbon in preference to silylation at nitrogen.Experimental data indicated that the 10-carbon of 5 was silylated directly with chlorotrimethylsilane. - Keywords: Antiaromatic character, Dibenzoazapentalene anions, Electron transfer; Elimination; Lithiation; Silylation