Katalysatorfreie enantiospezifische Olefinierung mithilfe von in situ generierten Organocer‐Spezies

Transition Metal Catalyst-Free, Base-Promoted 1,2-Additions of Polyfluorophenylboronates to Aldehydes and Ketones

A novel protocol for the transition metal-free 1,2-addition of polyfluoroaryl boronate esters to aldehydes and ketones is reported, which provides secondary alcohols, tertiary alcohols, and ketones. Control experiments and DFT calculations indicate that both the ortho-F substituents on the polyfluorophenyl boronates and the counterion K+ in the carbonate base are critical. The distinguishing features of this procedure include the employment of commercially available starting materials and the broad scope of the reaction with a wide variety of carbonyl compounds giving moderate to excellent yields. Intriguing structural features involving O-H⋅⋅⋅O and O-H⋅⋅⋅N hydrogen bonding, as well as arene-perfluoroarene interactions, in this series of racemic polyfluoroaryl carbinols have also been addressed.

CeCl3 /n-BuLi: Unraveling Imamoto's Organocerium Reagent

CeCl₃(thf) reacts at low temperatures with MeLi, t‐BuLi, and n‐BuLi to isolable organocerium complexes. Solvent‐dependent extensive n‐BuLi dissociation is revealed by ⁷Li NMR spectroscopy, suggesting “Ce(n‐Bu)₃(thf)_x” or solvent‐separated ion pairs like “[Li(thf)₄][Ce(n‐Bu)₄(thf)_y]” as the dominant species of the Imamoto reagent. The stability of complexes Li₃Ln(n‐Bu)₆(thf)₄ increases markedly with decreasing Ln^III size. Closer inspection of the solution behavior of crystalline Li₃Lu(n‐Bu)₆(thf)₄ and mixtures of LuCl₃(thf)₂/n‐BuLi in THF indicates occurring n‐BuLi dissociation only at molar ratios of <1:3. n‐BuLi‐depleted complex LiLu(n‐Bu)₃Cl(tmeda)₂ was obtained by treatment of Li₂Lu(n‐Bu)₅(tmeda)₂ with ClSiMe₃, at the expense of LiCl incorporation. Imamoto's ketone/tertiary alcohol transformation was examined with 1,3‐diphenylpropan‐2‐one, affording 99 % of alcohol.

Tandem Mn-I Exchange and Homocoupling Processes Mediated by a Synergistically Operative Lithium Manganate

Pairing lithium and manganese(II) to form lithium manganate [Li₂ Mn(CH₂ SiMe₃ )₄ ] enables the efficient direct Mn-I exchange of aryliodides, affording transient (aryl)lithium manganate intermediates which in turn undergo spontaneous C-C homocoupling at room temperature to furnish symmetrical (bis)aryls in good yields under mild reaction conditions. The combination of EPR with X-ray crystallographic studies has revealed the mixed Li/Mn constitution of the organometallic intermediates involved in these reactions, including the homocoupling step which had previously been thought to occur via a single-metal Mn aryl species. These studies show Li and Mn working together in a synergistic manner to facilitate both the Mn-I exchange and the C-C bond-forming steps. Both steps are carefully synchronized, with the concomitant generation of the alkyliodide ICH₂ SiMe₃ during the Mn-I exchange being essential to the aryl homocoupling process, wherein it serves as an in situ generated oxidant.

Electro-Olefination-A Catalyst Free Stereoconvergent Strategy for the Functionalization of Alkenes

Conventional methods carrying out C(sp2 )-C(sp2 ) bond formations are typically mediated by transition-metal-based catalysts. Herein, we conceptualize a complementary avenue to access such bonds by exploiting the potential of electrochemistry in combination with organoboron chemistry. We demonstrate a transition metal catalyst-free electrocoupling between (hetero)aryls and alkenes through readily available alkenyl-tri(hetero)aryl borate salts (ATBs) in a stereoconvergent fashion. This unprecedented transformation was investigated theoretically and experimentally and led to a library of functionalized alkenes. The concept was then carried further and applied to the synthesis of the natural product pinosylvin and the derivatization of the steroidal dehydroepiandrosterone (DHEA) scaffold.