Asymmetric Defluoroallylation of 4-Trifluoromethylpyridines Enabled by Umpolung C-F Bond Activation

Carbon-fluorine bond activation reaction of the trifluoromethyl group represent an important approach to fluorine-containing molecules. While selective defluorofunctionalization reactions of CF3-containing substrates have been achieved by invoking difluorocarbocation, difluorocarboradical, or difluoroorganometallic species as the key intermedi-ate, the transformations via fluorocarbanion mechanism remained a limited success. Furthermore, the enantioselective defluorotransformation of CF3 group has not yet been realized. Herein, we report a defluorofunctionalization reaction of 4-trifluoromethylpyridines involving pyridyldifluoromethyl anion as the key intermediate, which was developed based upon our previous studies on the N-boryl pyridyl anion chemistry. When combined with Ir-catalysis, asymmetric defluoroallylation of 4-trifluoromethylpyridines could be achieved to forge a difluoroalkyl-substituted chiral center. The present work opens up a new opportunity for the defluorofunctionalization of CF3 group, and provides new insights into the N-boryl pyridyl anion chemistry.

Efficient room temperature catalytic synthesis of alternating conjugated copolymers via C-S bond activation

Structural defects in conjugated copolymers are severely detrimental to the optoelectronic properties and the performance of the resulting electronic devices fabricated from them. Therefore, the much-desired precision synthesis of conjugated copolymers with highly regular repeat units is important, but presents a significant challenge to synthetic materials chemists. To this end, aryl sulfides are naturally abundant substances and offer unrealized potential in cross-coupling reactions. Here we report an efficient room temperature polycondensation protocol which implements aryl disulfide C-S activation to produce defect-minimized semiconducting conjugated copolymers with broad scope and applicability. Thus, a broad series of arylstannanes and thioethers are employed via the present protocol to afford copolymers with number-average molecular weights (Mns) of 10.0–45.0 kDa. MALDI and NMR analysis of selected copolymers reveals minimal structural defects. Moreover, the polymer trap density here is smaller and the field effect mobility higher than that in the analogous polymer synthesized through thermal-activation Stille coupling.

How Rhodium(I)-Catalyzed Phosphorus(III)-Directed C–H Bond Functionalizations Can Improve the Catalytic Activities of Phosphines

Trivalent-phosphorus-containing molecules are widely used in fields ranging from catalysis to materials science. Efficient catalytic methods for their modifications, providing straightforward access to novel hybrid structures with superior catalytic activities, are highly desired to facilitate reaction improvement or discovery. We have recently developed new methods for synthesizing polyfunctional phosphines by C–C cross-couplings through rhodium-catalyzed C–H bond activation. These methods use a native P(III) atom as a directing group, and can be used in regioselective late-stage functionalization of phosphine ligands. Interestingly, some of the modified phosphines outperform their parents in Pd-catalyzed cross-coupling reactions.1 Introduction2 Early Examples of Transition-Metal-Catalyzed P(III)-Directed C–H Bond Activation/Functionalizations3 Synthesis of Polyfunctional Biarylphosphines by Late-Stage Alkylation: Application in Carboxylation Reactions4 Synthesis of Polyfunctional Biarylphosphines by Late-Stage Alkenylation: Application in Amidation Reactions5 Conclusion

Heterogeneous Iron Catalyst Fe/SBA-15 towards sp3 C-O bond activation in the absence of base and additive

A heterogeneous iron-catalyzed (8wt%Fe/SBA-15) mediated direct alkylation of benzyl alcohol with aryl boronic acid in the absence of base and additive via C-O bond activation is demonstrated. This catalyst system led to an efficient Friedel-crafts alkylation reaction. The acidic site in the catalyst system had been confirmed by NH3-TPD, which shows the presence of three different acidic sites viz., weak, moderated, and strong acid sites. The catalyst showed five times recyclable ability.