Mechanistic Information from Nonstationary Points

Abstract

The thermal cyclization of enyne-carbodiimides substituted at both the alkyne and carbodiimide terminus showed two curved Hammett correlations (log k/k0 against σp) that were fully reproduced by DFT (density functional theory) computational results. The latter suggest a concerted mechanism, but the transition state (TS) analysis failed to reveal any mechanistic insight about the reason for a curved Hammett correlation. Instead a preTS inspection, i.e., examination of the electronic and steric details on route between reactant and TS, furnished a detailed picture of the mechanism.

Iron‐Catalyzed C−H Activation with Propargyl Acetates: Mechanistic Insights into Iron(II) by Experiment, Kinetics, Mössbauer Spectroscopy, and Computation

“…A Hammett plot analysis of the initial rates of the ironcatalyzed CÀH activation with a range of substrates 2 showed a change in the slope (k X /k H ), which can, among others, be explained by a change in the rate-determining step (Scheme 3). [8] C À D/N À H functionalization with the isotopically labeled substrates As to the catalysts mode of action, detailed Mçssbauer spectroscopic studies were performed to reveal the oxidation state of the iron species. Our observations provided strong support for the presence of high-spin iron(II) intermediates (Table 2).…”

Microwave-Assisted Cascade Strategy for the Synthesis of Indolo[2,3-b]quinolines from 2-(Phenylethynyl)anilines and Aryl Isothiocynates

“…On the basis of our experimental findings and previous literature, a plausible reaction mechanism has been proposed as depicted in Scheme . Reaction of 2-(phenylethynyl)­anilines ( 1 ) and phenyl isothiocynate ( a ) forms intermediate thiourea ( A ), which is desulfurized in the presence of Ag 2 CO 3 to a carbodiimide intermediate ( B ) .…”

“…For these reasons, over the past several years, tremendous effort has been devoted to the synthesis of such tetracyclic-fused quinoline alkaloids both by organic and medicinal chemists with the aim of enhancing the potency of indolo­[2,3- b ]­quinoline, and a variety of approaches have been successfully developed . Most of the available synthetic strategies rely on the use of indole and its derivative as one of the coupling partners. , The indoloquinoline system has also been assembled through a thermal cyclization of an enyne–carbodiimide . In 2003, Curran et al reported the synthesis of indolo­[2,3- b ]­quinoline via a cascade radical annulation of o -alkynylthiourea that involves irradiation of UV light (with medium pressure Hg lamp) in a Pyrex glass tube requiring a large excess of tris­(trimethylsilyl)­silane (TTMSS) (4 equiv) and AIBN (1 equiv) in anhydrous benzene (Scheme a) .…”

Eisenkatalysierte C‐H‐Aktivierung mit Propargylacetaten: Mechanistische Einblicke in Eisen(II) durch Experiment, Kinetik, Mössbauer‐Spektroskopie und Berechnung

“…[Fe] Ligand Angewandte Chemie (Schema 3). [8] C-D/N-H-Funktionalisierungen mit den Isotopen-markierten Amiden Zur Wirkungsweise des Katalysators wurden detaillierte Mçssbauer-spektroskopische Untersuchungen durchgeführt, um die Oxidationsstufen der Eisenspezies aufzudecken. Unsere Beobachtungen haben dabei die Anwesenheit von High-spin-Eisen(II)-Zwischenstufen bestätigt (Tabelle 2).…”