A Radical Roundabout for an Unprecedented Tandem Reaction Including a Homolytic Substitution with a Titanium‐Oxygen Bond

Abstract

Conceptually novel homolytic substitutions (SH2) of ClCp2Ti−O bonds with benzylic, secondary and tertiary alkyl radicals are described. The intermediates and crucial transition structures were studied by DFT methods. The resulting atom economical radical tandem reaction can be utilized for the synthesis of structurally complex tetrahydrofurans from simple starting materials and is therefore of interest for natural product synthesis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Computational study of the rate constants and free energies of intramolecular radical addition to substituted anilines

“…Radical-based transformations are amongst the most attractive methods for the use in catalytic cycles due to the ease of radical generation, high functional group tolerance, and selectivity in C–C bond formation [3–5]. Recently, we have reported a novel catalytic reaction, a radical arylation of epoxides [6–8] proceeding via catalysis in single electron steps (for experimental results see Scheme 1) [9–10]. The C–C bond forming step of the catalytic cycle is an intramolecular alkyl radical addition to substituted anilines.…”

The Nugent Reagent: A Formidable Tool in Contemporary Radical and Organometallic Chemistry

“…Despite the thermodynamic preference for trans radical intermediates over cis ones, the formation of the cis ‐tetrahydrofuran ring is kinetically favoured according to the Beckwith–Houk rules 57. Experimental and theoretical data55,58 indicate only the formation of the cis ‐tetrahydrofuran ring (Scheme ).…”

Cp2TiX Complexes for Sustainable Catalysis in Single‐Electron Steps

“…This reaction is challenging for two reasons. First, the reductive elimination is significantly more difficult because a stabilized benzylic radical is consumed in tetrahydrofuran formation rather than an alkyl radical as for 17S . Second, 18P is sensitive to acidic conditions because a stabilized benzylic cation is formed after acid‐induced ring opening.…”

“…With titanocene(III) complexes, epoxides were used as radical precursors in oxidative additions to generate β‐titanoxy radicals . These intermediates have been used in atom‐economical syntheses of polycyclic tetrahydrofurans, and in atom‐economical radical arylations through catalysis in single‐electron steps. In both cases, the reductive elimination is critical for catalytic turn‐over (Scheme ).…”