Keteniminium Salts: Reactivity and Propensity toward Electrocyclization Reactions

A predictive computational study was conducted in order to assess the efficiency of electrocyclization reactions of keteniminium salts, in an effort to form a variety of heterocyclic systems, namely, 3-amino­(benzo)­thiophenes, 3-amino­(benzo)­furans, 3-aminopyrroles, as well as 3-aminoindoles. A density functional theory (DFT) approach was utilized and the effect of heteroatoms (NMe, O, S) was thoroughly investigated by means of population analysis, QTAIM, NICS, ACID, and local reactivity descriptors (Parr and Fukui functions). The electrocyclization of enamines leading to 3-aminopyrroles was shown to be both kinetically and thermodynamically most favorable. Moreover, the pericyclic nature of the electrocyclizations was confirmed using FMO, QTAIM, NICS, and ACID methods. Additionally, substituent effects were investigated in order to give further insight on the reactivity of heteroatom containing keteniminium systems toward electrocyclization reactions. Finally, computational predictions were experimentally confirmed for a selection of keteniminium systems.