Ring transformations of heterocyclic compounds. XV. N-(2-hydroxyphenyl) substituted 2-alkylamino-4,6-diarylbenzophenones by ring transformation of 2,4,6-triarylpyrylium salts with anhydrobases of benzoxazolium salts

The synthesis of hitherto unknown N-(2-hydroxyphenyl) substituted 2-alkylamino-4,6-diarylbenzophenones 3 from 2,4,6-triarylpyrylium salts 1 and 3-alkyl-2-methylbenzoxazolium salts 2 in the presence of triethylamine in ethanol by a 2,5-[C₄+C₂] pyrylium ring transformation is reported. Structure elucidation is performed by an X-ray crystal structure determination of the benzophenone 3a. Spectroscopic data of the transformation products and their mode of formation via anhydrobases of the salts 2 are discussed.