Pyryliumverbindungen. 33 [1] 2-Dialkylamino-2H-thiopyrane aus 2,4,6-Triaryl-thiopyryliumsalzen

Pyrylium Compounds. 33. 2-Dialkylamino-2H-thiopyrans from 2,4,6-Triaryl-thiopyrylium Salts 2,4,6-Triaryl-thiopyrylium salts 7 react with dialkylamines in diethyl ether to give stable crystalline 2-dialkylamino-2H-thiopyrans 8 , the structure of which is in accordance with their u.v., n.m.r. and mass spectra. The chemical properties of 8 parallel those of structurally analogous 2-alkoxy- and 2-dialkylamino-2H-pyrans and 2-alkoxy-2H-thiopyrans. Thus, on heating 2-dimethylamino-2,4,6-triphenyl-2H-thiopyran ( 8a ) with methanol the corresponding 2-methoxy-2H-thiopyran 9 is formed. Nitromethane and ethyl cyanoacetate give rise to ring transformations yielding 1,3,5-triphenyl benzene ( 10 ) and 2,4,6-benzonitrile ( 11 ), respectively. From 8a electrophiles (e.g. mineral acids, methyl iodide, benzoyl chloride) regenerate the initial thiopyrylium system by taking over the dialkylamino group.