title: Nucleophilic additions to alkylidene bis(sulfoxides): stereoelectronic effects in vinyl sulfoxides.
abstract: Conjugate additions of nucleophiles (e.g. enolates, amines and malonate anions) to bis(p-tolylsulfinyl)alkenes, alkylidene-1,3-dithiane-1,3-dioxides and alkylidene-1,3-dithiolane-1,3-dioxides have recently been published. Reasons for different selectivities and reaction rates will be discussed by consideration of steric and electronic effects. The preferred mode of attack can be explained by stereoelectronic effects (hyperconjugation) in the primarily carbanion, which is stabilized by n-->S-O-sigma* interaction with an antiperiplanar S=O group. Calculation of the transition states [BP86/aug-TZVP] for the addition of acetone enolate to the dithiane-derived alkylidene bis(sulfoxide) revealed that 6.6-7.3 kJ mol(-1) more energy is needed for an attack leading to a less-stabilized carbanion. Two axial S=O groups in dithiolane-derived alkylidene bis(sulfoxides) lead to a higher reactivity towards nucleophiles.
authors.affiliation: Institut für Organische Chemie, Universität Karlsruhe TH, Karlsruhe, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Wedel
authors.forename: Timo
authors.initials: T
authors.lastname: Gehring
authors.forename: Joachim
authors.initials: J
authors.lastname: Podlech
authors.forename: Elena
authors.initials: E
authors.lastname: Kordel
authors.forename: Angela
authors.initials: A
authors.lastname: Bihlmeier
authors.forename: Wim
authors.initials: W
authors.lastname: Klopper