The synthesis and reactions of sterically constrained pyrylium and pyridinium salts

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Abstract
Efficient syntheses are developed for several pyrylium cations with substitution patterns more strictly demanding than 2,4,6-triphenyl and these are examined as reagents for the conversion of primary into a leaving group, The 2-mesityl-4,6-diphenyl derivative did not react smoothly with amines. The 2,6-di-t-butyl-4-phenyl-pyrylium cation gave the corresponding pyridinium derivatives, but they resisted nucleophillic attack 2-t-butyl-4,6-diphenylpyridinium cations suffer nucleophilic attack with about the same case as the 2,4,6-triphenyl analogues. Dihydrobenzopyrylium (6) and tetrahydrodibenzoxanthylium cations (7) gave pyridinium cations which underwent much easier nucleophilic attack: thus they alkylate xanthate anion in ethanol solution and acetate anion in acetic acid.

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