Ring transformations of heterocyclic compounds. XX Benzo‐fused spiro[cyclohexadiene‐dihydroindoles] by ring transformation of pyrylium salts with anhydrobases of benzo[e]‐ and benzo[g]indolium salts

The diastereoselective synthesis of 6‐aroyl‐3,5‐diarylspirocyclohexa‐2,4‐diene‐1,2′2′,3′‐dihydro‐1′H‐benzoe]indoles] 6 and ‐benzog]indoles] 7 from 2,4,6‐triarylpyrylium perchlorates 1 and in situ generated 2‐methylene‐2,3‐dihydro‐1H‐benzoe]indoles 3 or ‐benzog]indoles 5 (anhydrobases of the corresponding 2‐methyl‐1H‐benzoe]indolium perchlorates 2 and 2‐methyl‐3H‐benzog]indolium perchlorates 4 , respectively) in the presence of triethylamine/acetic acid in ethanol by a 2,5‐C₄+C₂] pyrylium ring transformation is reported. Spectroscopic data of the transformation products and their mode of formation are discussed.