title: Computational Mechanistic Study of Thionation of Carbonyl Compounds with Lawesson's Reagent.
abstract: The thionation reaction of carbonyl compounds with Lawesson's reagent (LR) has been studied using density functional theory methods and topological analyses. After dissociation of LR, the reaction takes place through a two-step mechanism involving (i) a concerted cycloaddition between one monomer and the carbonyl compound to form a four-membered intermediate and (ii) a cycloreversion leading to the thiocarbonyl derivative and phenyl(thioxo)phosphine oxide. Topological analyses confirmed the concertedness and asynchronicity of the process. The second step is the rate-limiting one, and the whole process resembles the currently accepted mechanism for the lithium salt-free Wittig reaction. No zwitterionic intermediates are formed during the reaction, although stabilizing electrostatic interactions are present in initial stages. Phenyl(thioxo)phosphine oxide formed in the thionation reaction is capable of performing a second thionation, although with energy barriers higher than the first one. The driving force of the thionation reactions is the formation of trimers from the resulting monomers. In agreement with experimental observations, the amides are the most reactive when compared with esters, aldehydes, and ketones and the reaction is slightly influenced by the polarity of the solvent. Whereas for amides and esters substituents have little effect, aldehydes and ketones are influenced by both steric and electronic effects.
authors.affiliation: Dipartimento di Chimica, Università di Pavia , Via Taramelli 12, 27100 Pavia, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Legnani
authors.affiliation: Dipartimento di Chimica, Università di Pavia , Via Taramelli 12, 27100 Pavia, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Toma
authors.affiliation: Dipartimento di Chimica, Università di Pavia , Via Taramelli 12, 27100 Pavia, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Caramella
authors.affiliation: Dipartimento di Chimica, Università di Pavia , Via Taramelli 12, 27100 Pavia, Italy.|Dipartimento di Scienze del Farmaco, Università di Catania , V. le A. Doria 6, 95125 Catania, Italy.
authors.forename: M A
authors.initials: MA
authors.lastname: Chiacchio
authors.affiliation: Dipartimento di Scienze chimiche, biologiche, farmaceutiche e ambientali, Università di Messina , Via Stagno d'Alcontres, 98166 Messina, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Giofrè
authors.affiliation: Laboratorio de Síntesis Asimétrica, Instituto de Síntesis Quimica y Catalisis Homogenea (ISQCH), Universidad de Zaragoza-CSIC , Zaragoza 50009, Spain.
authors.forename: I
authors.initials: I
authors.lastname: Delso
authors.affiliation: Laboratorio de Síntesis Asimétrica, Instituto de Síntesis Quimica y Catalisis Homogenea (ISQCH), Universidad de Zaragoza-CSIC , Zaragoza 50009, Spain.
authors.forename: T
authors.initials: T
authors.lastname: Tejero
authors.affiliation: Laboratorio de Síntesis Asimétrica, Instituto de Síntesis Quimica y Catalisis Homogenea (ISQCH), Universidad de Zaragoza-CSIC , Zaragoza 50009, Spain.
authors.forename: P
authors.initials: P
authors.lastname: Merino