Eine neue einfache Synthese spirocyclischer 1H‐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 I2 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 1H‐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′(1H)‐quinolines] (Scheme 3).