Ring transformations of heterocyclic compounds. XXI. Diastereoselective built‐up of an aroylcyclohexadiene moiety as second spiro‐connected ring at spiroindolines by pyrylium ring transformation

Abstract

Abstract2,4,6‐Triarylpyrylium perchlorates 1 react with methyleneindolines 3 in situ generated from the corresponding methylindolium salts 2, which are spiro‐fused with a cycloalkane, benzanellated cycloalkene or a heterocyclic system. These diastereoselective 2,5‐[C4+C2] pyrylium ring transformations are carried out in the presence of triethylamine/acetic acid in boiling ethanol to give the dispiroindolines 4 with a trans configuration of the more bulky substituents at the cyclohexadiene ring. By the same type of transformation the dispiro compounds 7/10 with an additional fused benzene ring are obtained from the pyrylium salt 1a and 6/9, the benzo‐fused analogues of 3. Spectroscopic data of the transformation products as well as their mode of formation are discussed.