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Pyrylium Compounds. XXIII. 2-Dialkylamino-2H-pyrans from Tetra- and Pentasubstituted Pyrylium Salts
Fischer, Gerhard W.,Zimmermann, Thomas,Weissenfels, Manfred
, p. 657 - 666 (2007/10/02)
Tetra- and pentasubstituted pyrylium salts of type 6 react with secondary alkyl amines to give stable crystalline 2-dialkylamino-2H-pyrans 7.In the case of tetrasubsituted pyrylium salts 6, R' = Me, R'' = H the reaction occurs regioselectively leading to 2H-pyrans with Me at C-3 of the heterocyclic ring.The structure of the reaction products was established by n.m.r., i.r., u.v. and mass spectroscopic methods.Electrophilic agents like protons, carboxylic acid chlorides or methyl iodide regenerate the original pyrylium cations from 7.In refluxing methanol 7a is converted into the 2-methoxy-2H-pyran derivative 8, whereas in aqueous acetone the pseudobase 9 and with ammonia the pyridine 10 are formed.Reaction of 7a with nitromethane or ethyl cyanoacetate provides the benzene derivatives 11 and 12, respectively.
