INTRAMOLECULAR INVERSE ELECTRON DEMAND DIELS-ALDER REACTIONS OF PYRAZINES

Article abstract of DOI:10.1016/S0040-4020(01)85132-2

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-propynyloxyethyl)pyrazine; the presence of a trimethylsilyl group at the terminus of the alkyne decreases in general the rate of the intramolecular cyclisation.The mechanisms are discussed.