79889-00-2Relevant academic research and scientific papers
Pyrylium Compounds. XVIII. 2-Alkoxy-2H-pyrans from Tetra- and Pentasubstituted Pyrylium Salts
Fischer, Gerhard W.,Zimmermann, Thomas,Weissenfels, Manfred
, p. 729 - 741 (2007/10/02)
Alkali alkoxides add regioselectively to 2,3,4,6-tetrasubstituted pyrylium salts 7 (R'=H), affording high yields of colourless crystalline 2-alkoxy-2H-pyrans 9.The latter are also formed simply on refluxing 7 in the corresponding alcohol with triethylamine as proton acceptor. 3,5-Dialkylsubstitued 2,4,6-trialkylpyrylium salts react analogously.The 2H-pyran structure of the adducts obtained follows from their n.m.r., i.r., u.v. and mass spectra as well as from their reaction with tetracyanoethylene to cycloadducts of type 10.Acids regenerate from 9 the original pyrylium cations, whereas reaction of 9 with nitromethane or ethyl cyanoacetate provides benzene derivatives. - The novel starting pyrylium salts 7b-o are characterized by u.v./vis data and by transformation into the corresponding pyridine derivatives.
