Eine neue einfache Synthese spirocyclischer 1 H ‐Chinolin‐Derivate

A New and Simple Method for the Synthesis of Spirocyclic la‐Quinolines The reaction of anilines with (+)‐( R )‐pulegone in toluene at temperatures between 125 and 150° with 4‐toluenesulfonic acid or I 2 as catalysts leads to diastereoisomeric mixtures of spiro[cyclohexane‐1,2′(1′ H )‐quinoline] derivatives (see 1–4 , Scheme 1; Table ). The diastereoisomers are separated by column chromatography, and the structure of the single isomers is determined by NMR‐spectroscopic methods. A reaction mechanism proceeding via several 6π‐electrocyclic rearrangements and H‐shifts is proposed for the formation of 1 H ‐quinolines 1–4 ( Scheme 2 ). This mechanism is in accordance with the results of the reaction of 2‐isopropenylaniline with 3‐methylcyclohexanone which leads to a stereoisomeric mixture of 3,4′‐dimethylspiro[cyclohexane‐1,2′(1 H )‐quinolines] ( Scheme 3 ).