Iodine-catalyzed formation of aza-dienes: a novel synthesis of angularly fused hexahydropyrano- and furo[3,2-c]quinoline derivatives

In situ generated aza-diene, from N-[methyl-N-(trimethylsilyl)methyl]aniline in the presence of a catalytic amount of molecular iodine undergoes smooth [4+2] cycloaddition with electron-rich enol ethers, such as 3,4-dihydro-2H-pyran and 2,3-dihydrofuran under mild and neutral conditions to afford the corresponding hexahydropyrano- and furo[3,2-c]quinoline derivatives, respectively, in good yields with cis-selectivity.