Theoretical Studies on the Reactions of Aryl and Hetaryl Thioketones with Nitrilimines
Many synthetic routes to constructing biologically-active heterocyclic compounds are made feasible through the (3 + 2) cycloaddition 32CA reactions. Due to a large number of possible combinations of several heteroatoms from either the three-atom components (TACs) or the ethylene derivatives, the potential of the 32CA reactions in heterocyclic syntheses is versatile. Herein, the 32CA of thiophene-2-carbothialdehyde derivatives and C,N-disubstituted nitrilimines have been studied through density functional theory (DFT) calculations at the B3LYP/6-311G(d,p) level of theory. In the present study, one-step (3 + 2) and two-step (4 + 3) mechanisms of the addition of the TAC and ethylene derivative have been investigated. In all reactions considered, the one-step (3 + 2) cycloaddition is preferred over the two-step (4 + 3) cycloaddition. The TAC chemoselectively adds across the thiocarbonyl group present in the ethylene derivative in a (3 + 2) fashion to form the corresponding cycloadduct. Analysis of the electrophilic ( and nucleophilic ( Parr functions at the various reaction centers in the ethylene derivative show that the TAC adds across the atomic centers with the largest Mulliken atomic spin densities, which is in total agreement with the experimental observation. The selectivities observed in the title reaction are kinetically controlled.