Ring transformations of heterocyclic compounds. XIX. Spiro [dihydropyridine-indolines] novel heterocycles with two spiro-condensed N-containing subunits easy accessible by 1,3-oxazinium ring transformation

The synthesis of hitherto unknown 1-benzoyl-1',3',3'-trimethyl-4,6-diphenylspiro[1,2-dihydropyridine-2,2'-indolines] 5 from 2,4,6-triphenyl-1,3-oxazinium tetrafluoroborate (1b) and 1,3,3-trimethyl-2-methyleneindolines 2 (used as such or generated ill situ from the corresponding 3H-indolium salts 4) in the presence of triethylamine in anhydrous acetonitrile by a 3,6-[C3N+C-2] 1,3-oxazinium ring transformation is reported. Structure elucidation is performed by an X-ray structure determination of the spiro[dihydropyridine-indoline] 5a. Spectroscopic data of the transformation products and their mode of formation are discussed.