INTRAMOLECULAR INVERSE ELECTRON DEMAND DIELS-ALDER REACTIONS OF PYRAZINES
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.
Biedrzycki, Marek,Bie, Dick A. de,Plas, Henk C. van der
p. 6211 - 6220
(2007/10/02)
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