Thiopyrylium salts, reaction with amines

Any preparative utilization of the addition reactions of thiopyrylium salts with amines appears to be significantly dependent on the nucleophili-... 

Amines also react with thiopyrylium salts to give pyridinium salts, but the reaction goes less easily than with the pyrylium analogues. 1,3-Oxazinium and 1,3-thiazinium cations react with ammonia and primary amines to give pyrimidines and pyridinium cations, respectively. 

The reaction of thiopyrylium salts with amines can afford different products, depending on the substitution pattern of the heteroaromatic cation, the nature of the amine, and reaction conditions. In most cases... 

A number of 2,4,6-triarylthiopyrylium salts reacts with dialkylamines in diethyl ether to give stable crystalline 2-dialkylamino-2//-thiopyrans (83ZC144 84EGP212964 86JPR567). Reactions of these with a number of nucleophiles and electrophiles can be easily accounted for by considering them in equilibrium with the parent thiopyrylium ion and amine (86JPR567). 

Many further examples have been given of the preparation of mixtures of thiopyrylium salts and the corresponding tetrahydrothiopyrans, by the action of hydrogen sulphide and various acids on 1,5-diketones. Selenopyrylium salts have also been prepared by this method. 2-Amino-6-methylthio-thiopyrylium salts, obtained by methylation of the related 2H-thiopyran-2-thiones, react with aromatic amines to give 2-arylimines (42). 2-Amino-6-arylthiopyrylium salts have also been prepared, from 3-mercaptovinylacrylonitriles, by an extension of a reaction previously used for the synthesis of 2-aminopyrylium and pyridinium salts. Several theoretical treatments have appeared. Non-empirical calculations suggest that the 3d orbitals are used only to a trivial extent," but, in another study, the conclusion is reached that involvement of the d-orbitals may be important, and that contributions of forms of type (43) to the hybrid... 

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