1-Methoxycarbonyl-substituiertes 2,3-Dihydropyridin-4(1<i>H</i>)-on (= Methyl-1,2,3,4-tetrahydro-4-oxopyridin-1-carboxylat) als Chromophor für die photochemische [2 + 2]-Cycloaddition

With olefins having an electron-acceptor as well as with olefins having an electron-donor substituent, 1-methoxycarbonyl-substituted dihydropyridinone <b>12</b> undergoes [2 + 2] cycloaddition in good preparative yields. The photochemical cycloaddition is highly regioselective. For preparative purposes, the ring junction can be equilibrated to the thermodynamically more stable cis-junction. Only the <i>’endo’/’exo’</i> selectivity at the C-atom bearing the olefin substituent cannot be controlled. The photodimerization of <b>12</b> is the only side reaction. Using a slight excess of the olefin, the photodimerization can be suppressed. The protecting group at the N-atom of the dihydropyridinone can be varied in order to introduce an internal sensitizer, as shown with 1-acyl-substituted compound <b>29</b>, which underwent the cycloaddition process even with sunlight.