Thermally induced intramolecular Diels-Alder cyclisations of (alkynyloxyalkyl) pyrazines to dihydropyranopyridines have been studied in the solvent undecane. The introduction of a phenyl group in the α-position of the 3-butynyloxymethyl side chain leads to a 3–4 fold increase of the reaction rate, while the influence of a γ-phenyl group on the rate is negligible. The (3-butynyloxymethyl) pyrazine reacts about 7 times slower than the (3- ...