B(C6F5)3-Catalyzed transfer 1,4-hydrostannylation of α,β-unsaturated carbonyls using iPr-tricarbastannatrane

Synthesis and Catalytic Activity of Atrane-type Hard and Soft Lewis Superacids with a Silyl, Germyl, or Stannyl Cationic Center

The synthesis and isolation of atrane-type molecules 1E⁺ (E=Si, Ge, or Sn) having a cationic group 14 elemental center are reported. The cations 1E⁺ act as hard and soft Lewis superacids, which readily interact with various hard and soft Lewis basic substrates. The rigid atrane framework stabilizes the localized positive charge on the elemental center and assists the formation of the well-defined highly coordinated states of 1E⁺ . The cations were applied to the hydrodefluorination, Friedel-Crafts reaction, alkyne cyclization, and carbonyl reduction as Lewis acid catalysts. Most notably, [1Si][ClO₄ ] exhibits unique chemoselectivity that depends on a solvent in the competitive reaction of silyl enol ether with a mixture of benzaldehyde dimethyl acetal and benzaldehyde. Our findings indicate the potential of hard and soft Lewis superacids in organic synthesis.

Preparation of Enantioenriched Alkylcarbastannatranes via Nucleophilic Inversion of Alkyl Mesylates for Use in Stereospecific Cross-Coupling Reactions

We report the preparation of enantioenriched secondary alkylcarbastannatranes via a stereoinvertive S_N2 reaction of enantioenriched alkyl mesylates and carbastannatranyl anion equivalents. Using this process, enantioenriched secondary alcohols may be converted into highly enantioenriched alkylcarbastannatranes, which are useful in stereospecific cross-coupling reactions.

Stereospecific Electrophilic Fluorination of Alkylcarbastannatrane Reagents

We report the use of isolable primary and secondary alkylcarbastannatrane nucleophiles in site-specific fluorination reactions. These reactions occur without the need for transition metal catalysis or in situ activation of the nucleophile. In the absence of the carbastannatrane backbone, alkyltin nucleophiles exhibit no activity towards fluorination. When enantioenriched alkylcarbastannatranes are employed, fluorination occurs predominately via a stereoinvertive mechanism to generate highly enantioenriched alkyl fluoride compounds. These conditions can also be extended to stereospecific chlorination, bromination, and iodination reactions.

Single Electron Delivery to Lewis Pairs: An Avenue to Anions by Small Molecule Activation

Single electron transfer (SET) reactions are effected by the combination of a Lewis acid (e.g., E(C₆F₅)₃ E = B or Al) with a small molecule substrate and decamethylferrocene (Cp*₂Fe). Initially, the corresponding reactions of (PhS)₂ and (PhTe)₂ were shown to give the species [Cp*₂Fe][PhSB(C₆F₅)₃] 1 and [Cp*₂Fe][(μ-PhS)(Al(C₆F₅)₃)₂] 2 and [Cp*₂Fe][(μ-PhTe)(Al(C₆F₅)₃)₂] 3, respectively. Analogous reactions with di-tert-butyl peroxide yielded [Cp*₂Fe][(μ-HO)(B(C₆F₅)₃)₂] 4 with isobutene while with benzoyl peroxide afforded [Cp*₂Fe][PhC(O)OE(C₆F₅)₃] (E = B 5, Al 6). Evidence for a radical pathway was provided by the reaction of Ph₃SnH and p-quinone afforded [Cp*₂Fe][HB(C₆F₅)₃] 7 and [Cp*₂Fe]₂[(μ-O₂C₆H₄)(E(C₆F₅)₃)₂] (E = B 8, Al 9). In addition, the reaction of TEMPO with Lewis acid and Cp*₂Fe afforded [Cp*₂Fe][(C₅H₆Me₄NOE(C₆F₅)₃] (E = B 10, Al 11). Finally, reactions with O₂, Se, Te and S₈ gave [Cp*₂Fe]₂[((C₆F₅)₂Al(μ-O)Al(C₆F₅)₃)₂]₂ 12, [Cp*₂Fe]₂[((C₆F₅)₂Al(μ-Se)Al(C₆F₅)₃)₂]₂ 13, [Cp*₂Fe][(μ-Te)₂(Al(C₆F₅)₂)₃] 14 and [Cp*₂Fe]₂[(μ-S₇)B(C₆F₅)₃)₂] 15, respectively. The mechanisms of these SET reactions are discussed, and the ramifications are considered.