RING TRANSFORMATIONS OF HETEROCYCLIC-COMPOUNDS .12. NOVEL SPIROINDOLINES VIA RING TRANSFORMATION OF 2,4,6-TRIARYLPYRYLIUM SALTS WITH 2-METHYLENEINDOLINES
T. Zimmermann et M. Pink, RING TRANSFORMATIONS OF HETEROCYCLIC-COMPOUNDS .12. NOVEL SPIROINDOLINES VIA RING TRANSFORMATION OF 2,4,6-TRIARYLPYRYLIUM SALTS WITH 2-METHYLENEINDOLINES, Journal fur praktische Chemie, Chemiker-Zeitung, 337(5), 1995, pp. 368-374
2,4,6-Triarylpyrylium salts 1 react with 2-methyleneindolines 2 or the
ir 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 diastereomer
ically pure 5-diaryl-spiro[cyclohexa-2,4-diene-1,2'-indolines] 3, whic
h represent a novel type of spiroindoline compounds. When the 1'-pheny
l substituted spiroindolines 3 (R=Ph, R'=H) are treated with p-toluene
sulfonic acid in chloroform the 4,6-diaryl-2- [1-methyl-1- (2-phenylam
inophenyl) methyl]benzophenones 4 are obtained as the result of an int
ramolecular amine elimination. Structural elucidation of the reaction
products 3/4 is based on spectroscopic data and on an X-ray determinat
ion of the bis(4-bromophenyl) substituted spiroindoline 3i.