OLD REAGENTS, NEW RESULTS - AROMATIZATION OF HANTZSCH 1,4-DIHYDROPYRIDINES WITH MANGANESE DIOXIDE AND 2,3-DICHLORO-5,6-DICYANO-1,4-BENZOQUINONE

摘要

Hantzsch 1,4-dihydropyridines are readily oxidized by manganese dioxide or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in dichloromethane at room temperature. With manganese dioxide loss of the 4-substituent, in addition to aromatization, occurs when it is a secondary alkyl or a benzylic group and sonication significantly reduces the reaction times. In contrast, loss of the 4-substituent is never observed when DDQ is the oxidative species. [References: 43]