Cycloaddition of 1-methyl-2(1H)-quinolones with electron-withdrawing groups such as methoxycarbonyl, cyano, and acetyl groups, at the 3 or 4-position with 2,3-dimethoxy- and 2-(trimethylsilyloxy)-1,3-butadienes afforded stereoselectively phenanthridone derivatives under atmospheric and high pressures. Furthermore, regioselectivities of the cycloaddition of 3- or 4-substituted 2 (1H)-quinolones with 2-(trimethylsilyloxy)-1,3-butadiene were examined using MO calculation.