A density functional theory study of the chemoselectivity and regioselectivity of the domino cycloaddition reactions of nitroalkenes with substituted alkenes

The chemoselectivity and regioselectivity of the domino intermolecular 4 + 2]/3 + 2] cycloaddition reactions of nitroalkenes with substituted alkenes, vinyl ethers as electron-rich alkenes and vinyl ketones as electron-poor alkenes, have been studied using density functional theory (DFT) methods with the B3LYP functional and the 6-31G^* basis set. These domino processes comprise two consecutive cycloaddition reactions: the first one is an intermolecular 4 + 2] cycloaddition of the vinyl ether to the nitroalkene to give a nitronate intermediate, which then affords the final nitroso acetal adduct through an intermolecular 3 + 2] cycloaddition reaction with the vinyl ketone. The two consecutive cycloadditions present total chemoselectivity and ortho regioselectivity. While first 4 + 2] cycloaddition reaction takes place along the attack of the electron-rich alkene to nitroalkene, the 3 + 2] one takes place along the attack of the electron-poor alkene to the corresponding nitronate intermediate. This DFT study is in complete agreement with the experimental results. Received: 16 September 1999 / Accepted: 3 February 2000 / Published online: 2 May 2000