Three-Component Synthesis of Pyrano- and Furanoquinolines

Significance

A mild three-component aldehyde-aniline-enol ether synthesis of pyrano- and furanoquinolines via the Povarov reaction (see review below) under TMSCl-catalyzed conditions is reported. The reaction involving an aza-Diels-Alder step, proceeds in modest to excellent yields which appears not to be influenced greatly by substituent effects. However, higher trans:cis diastereomeric ratios of products are favored by use of aldehydes and anilines bearing electron-donating groups and by 3,4-dihydro-2H-pyran (n = 2) as the dienophile. In a solitary example, cyclohexanone was used to give a tetrahydrophenathridinone derivative in 87% yield.