RING TRANSFORMATIONS OF HETEROCYCLIC-COMPOUNDS .12. NOVEL SPIROINDOLINES VIA RING TRANSFORMATION OF 2,4,6-TRIARYLPYRYLIUM SALTS WITH 2-METHYLENEINDOLINES

2,4,6-Triarylpyrylium salts 1 react with 2-methyleneindolines 2 or their salts 2 HX in the presence of triethylamine/acetic acid in ethanol by a 2,5-[C-4 + C-2] pyrylium ring transformation to give diastereomerically pure 6-aroyl-3,5-diaryl-spiro[cyclohexa-2,4-diene-1,2'-indolines] 3, which represent a novel type of spiroindoline compounds. When the 1'-phenyl substituted spiroindolines 3 (R=Ph, R'=H) are treated with p-toluenesulfonic acid in chloroform the 4,6-diaryl-2- [1-methyl-1- (2-phenylaminophenyl) methyl]benzophenones 4 are obtained as the result of an intramolecular amine elimination. Structural elucidation of the reaction products 3/4 is based on spectroscopic data and on an X-ray determination of the bis(4-bromophenyl) substituted spiroindoline 3i.