3,4-DIHYDROQUINOLINIUM SALTS - PREPARATION BY REACTION OF N-ARYLNITRILIUM SALTS WITH ALKENES

N-Arylnitrilium salts 1 react with nucleophilic alkenes 2 to afford 3, 4-dihydroquinolinium salts 3, which can be transformed into the free b ases with aqueous sodium hydroxide. Dehydrogenation;of the 3,4-dihydro quinolinium salts 3 with 2,3-dichloro-5,6-dicyano-p-benzoquinone furni shes quinolinium salts 7. If the intermediate carbenium ion A formed b y electrophilic attack of 1 on the alkene 2 is conjugatively or hyperc onjugatively stabilized, instead of 3,4-dihydroquinolinium salts 3 imi nium salts 4 resulting from a Houben-Hoesch reaction, or iminium salts 5 arising from a formal ene reaction are formed. For the 3,4-dihydroq uinolinium salt 3ac X-ray structural analysis has been carried out. Co pyright (C) 1996 Elsevier Science Ltd