Stereo- and regiocontrol of electrophile-initiated rearrangement of push–pull 5-substituted 4-oxothiazolidine derivatives

Electrochemical reduction of (5-etoxycarbonylmethylidene-4-oxothiazolidine-2-ylidene)-N-phenylethanone in aprotic medium: A spectroelectrochemical approach

“…Presumably the anion radical resulted from the first ET belongs to the 1a isomer, obtained as majoritary isomer by synthesis [8,26]. The anion-radical is an electrogenerated base (EGB) and its diffusion into the bulk solution is followed by the deprotonation of the substrate leading to its conjugated base, the anion 1a À , and the free radical of the substrate 1a Å .…”

“…Over the last decade, the chemistry of an extensive series of 5-substituted and unsubstituted 4-oxothiazolidines, bearing the trisubstituted exocyclic CAC double bond at the C(2) position has been the subject of work in our laboratory [6][7][8]. The push-pull effect is of decisive influence on both the dynamic behaviour and the chemical reactivity of these compounds, which can exist in different configurational and conformational forms and have been previously characterized by 1 H NMR and 13 C NMR, IR, UV, MS spectroscopy and X-ray structural analysis [9,10].…”

“…1), synthesized as mixture of (2E,5Z)-1a and (2Z,5Z)-1b isomers according to procedure reported by our research group [8,10,26], in order to outline the role of the electron withdrawing substituent (EWG) on the electrochemical behaviour of selected 4-oxothiazolidines on both the reduction mechanism and the reactivity of the intermediate species. Research on redox properties of 1 may provide a better understanding of electron transfer processes involving heterocyclic push-pull alkenes.…”

Ethyl (E)-2-(4-oxo-1,3-thiazinan-2-ylidene)ethanoate

“…These reactions were found to take place without detectable traces of the competing six-membered 6-substituted 4-oxo-1,3-thiazinane derivatives (5), which could be formed from the key intermediates (3), which possess two electrophilic centres. However, the intermediates (3) readily undergo intramolecular cyclization only by path a, affording under kinetic control the stereodefined 4-oxothiazolidine derivatives (4) (Marković & Baranac, 1998;Marković et al, 2001). Therefore, (i) the sluggish heterocyclization reaction giving rise to the title compound under relatively drastic reaction conditions, and (ii) the exclusive formation of the five-membered heterocycles (4) without traces of (5) (Scheme, path a), rely critically on the lower tendency towards cyclization of the common intermediates (3) to give the six-membered heterocycles (5) (path b).…”

“…under kinetic control the stereodefined 4-oxothiazolidine derivatives (4) (Marković & Baranac, 1998;Marković et al, 2001). Therefore, (i) the sluggish heterocyclization reaction giving rise to the title compound under relatively drastic reaction conditions, and (ii) the exclusive formation of the five-membered heterocycles (4) without traces of (5) (Scheme, path a), rely critically on the lower tendency towards cyclization of the common intermediates (3) to give the six-membered heterocycles (5) (path b).…”