three-component cycloaddition with p-methoxybenzyl vinylether (1) and methyl acrylate to yield novel heteroaromatic-substituted six/five-membered bicyclic nitroso acetals. In the reaction of 3-[(E)-2-nitroeth-1-enyl]pyridine (2 equiv.) and 1 a competition between the formation of the tandem [4 + 2]/[3 + 2] cycloadducts and the formation of a novel five-membered cyclic nitronate was observed. The ratio