Novel Synthesis of 3,4,4-Trisubstituted Thiadiazolines from 3,4-Diphenyl-1,2,5-Thiadiazole 1,1-Dioxide. Competition with the Intra-Molecular Aryl-Aryl Cyclization of 3,4-Diphenyl-1,2,5-Thiadiazole 1,1-Dioxide

Abstract

3,4-Diphenyl-1,2,5-thiadiazole 1,1-dioxide (1) reacted, in the presence of anhydrous aluminum trichloride, with aromatic nucleophiles possessing electron donor substituent groups to give novel (2a-e, Figure [1] ) 3,4,4-trisubstituted 1,2,5-thiadiazoline 1,1-dioxides in good yield. In the presence of aluminum trichloride, but without the addition of nucleophiles, a slower, but practically quantitative intramolecular cyclization reaction (Scholl reaction [1] ) of 1 to phenanthro[9,10-c]-1,2,5-thiadiazole 1,1-dioxide (3), took place. Both reactions occur through the intermediation of a strong electrophile formed by 1 and aluminum trichloride. Spectral data and structure (through single-crystal X-ray diffraction, with the exception of 2c) were measured for all new compounds.