Abstract
2,4,6‐Triarylpyrylium salts 1 react with the in situ generated anhydrobase of 9,10‐dimethylacridinium methosulfate (2a) in the presence of anhydrous sodium acetate in ethanol by a 2,5‐[C4+C2] pyrylium ring transformation to give the hitherto unknown 6‐aroyl‐3,5‐diaryl‐10′‐methylspiro[cyclohexa‐2,4‐diene‐1,9′‐9′,10′‐dihydro‐acridines] 3. When the pyrylium perchlorate 1a is treated under the same conditions with the N‐ethyl, N‐allyl or N‐benzyl substituted acridinium salts 2b‐d a dealkylation of these salts occurs and the N‐unsubstituted spiro[cyclohexadiene‐dihydroacridine] 4a is formed. The same compounds 4 can also be obtained by transformation of the pyrylium salts 1 with 9‐methylacridine (7) and triefhylamine/acetic acid in ethanol. Structure elucidation is performed by an X‐ray crystal structure determination of the spiro[cyclohexadiene‐dihydroacridine] 3a. Spectroscopic data of the transformation products and their mode of formation are discussed.

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