Alkyl 2-Aryl-2-thioxoethanoates and -thioates: Preparation, Dimerization, and EPR Spectra of the Corresponding Radical Anions¹

Abstract

The title compounds were prepared by reaction of the corresponding α -halocarboxylic or α -halothiolocarboxylic esters with tetraethylammonium thiosulfate and subsequent treatment of the resulting Bunte salts with sodium hydroxide in a two-phase system. Under elimination of sulfite, the deep-blue colored thiones were generated. These labile compounds could not always be isolated from the solutions in a pure state. Instead, frequently the [2+2]-dimers (dialkyl 2,4-diaryl-1,3-dithietane-2,4-carboxylates) or other follow-up products were obtained. Nevertheless, the EPR spectra of the monomer radical anions could be recorded even if solutions of the dimers were reduced by internal electrolysis. Additional EPR spectra were observed in several cases, which we assign to the radical anions of dialkyl 2,3-diaryl-2-butene-1,4-dioate radical anions originating from electron induced sulfur extrusion of the corresponding 1,3-dithietanes. Radical trianions were observed when a 1,4-benzene-bis-α -thioxoester or -thioxo-thiolester was electroreduced at a more negative electrode potential.

Keywords:

• Benzo[c]thiophenes
• Bunte salts
• 1,3-dithietanes
• EPR spectroscopy
• radical anions
• 2-thioxocarboxylates

Dedicated to Professor Marian Mikołajczyk, CBMiM PAN in Łódź, Poland, on the occasion of his 70th birthday.

The University of Hamburg, the Konrad-Adenauer-Stiftung (gradute scholarship A. S.), the Deutsche Forschungsgemeinschaft, and the Fonds der Chemischen Industrie are gratefully acknowledged for their financial support. We thank Prof. Dr. U. Behrens, University of Hamburg, for his help concerning the X-ray structures.

Notes

^a Not determined.

^b a ^H _{4 - OMe}.

^c a ^N _NO2.

^d Not resolved.

^e Radical trianion, observed at E _red = −2.0 V, see text.

^f a ^H _{4 - COOMe}.

^g 2k = tBu-CS-CO-OEt.

^h a ^H _tBu.

^a a ^H _tBu

∗A. Sawluk passed away on July 29, 1991.