C?F Activation at Rhodium Boryl Complexes: Formation of 2‐Fluoroalkyl‐1,3,2‐Dioxaborolanes by Catalytic Functionalization of Hexafluoropropene

Fluorinated building blocks by C? F bond cleavage : Catalytic C? F activation reactions that give novel dioxaborolanes have been developed (see scheme). The reactions proceed at room temperature, and catalytic intermediates are presumably rhodium hydride and boryl species.

     

Palladium‐Catalyzed Direct C?H Arylation of Isoxazoles at the 5‐Position

A palladium‐catalyzed direct arylation of isoxazoles with aryl iodides has been achieved. The C H bond at the 5‐position is activated selectively to give coupling products in moderate to good yields. This direct arylation was applied to the synthesis of a spiro‐type chiral ligand, which proved to be most effective to the palladium‐catalyzed tandem cyclization of a dialkenyl alcohol.     

Rhodium(I)‐Catalyzed Enantioselective C?C Bond Activation

Relieving the strain : The rhodium(I)‐catalyzed activation of C C bonds in functionalized cyclobutanes opens a novel route to highly substituted carbo‐ and heterocycles. Particularly intriguing is the differentiation of enantiotopic C C bonds, which leads to the formation of highly enantiomerically enriched lactones, cyclopentanones, and cyclohexenones (see scheme).

     

Rhodium(I)‐Catalyzed Cycloisomerization of Benzylallene‐Alkynes through C?H Activation

The efficient Rh^I‐catalyzed cycloisomerization of benzylallene‐alkynes produced the tricyclo[9.4.0.0^3,8]pentadecapentaene skeleton through a C H bond activation in good yields. A plausible reaction mechanism proceeds via oxidative addition of the acetylenic C H bond to Rh^I, an ene‐type cyclization to the vinylidenecarbene–Rh^I intermediate, and an electrophilic aromatic substitution with the vinylidenecarbene species. It was proposed based on deuteration and competition experiments.     

Oxygen‐Promoted C?H Bond Activation at Palladium

[Pd(P(Ar)(tBu)₂)₂] ( 1 , Ar=naphthyl) reacts with molecular oxygen to form Pd^II hydroxide dimers in which the naphthyl ring is cyclometalated and one equivalent of phosphine per palladium atom is released. This reaction involves the cleavage of both C H and O O bonds, two transformations central to catalytic aerobic oxidizations of hydrocarbons. Observations at low temperature suggest the initial formation of a superoxo complex, which then generates a peroxo complex prior to the C H activation step. A transition state for energetically viable C H activation across a Pd peroxo bond was located computationally.     

Rhodium‐Catalyzed ortho‐Selective C?F Bond Borylation of Polyfluoroarenes with Bpin?Bpin

An ortho‐selective C F bond borylation between N‐heterocycle‐substituted polyfluoroarenes and Bpin‐Bpin with simple and commercially available [Rh(cod)₂]BF₄ as a catalyst is now reported. The reaction proceeds under mild reaction conditions with high efficiency and broad substrate scope, even toward monofluoroarene, thus providing a facile access to a wide range of borylated fluoroarenes that are useful for photoelectronic materials. Preliminary mechanistic studies reveal that a Rh^III/V catalytic cycle via a key intermediate rhodium(III) hydride complex [(H)Rh^IIIL_n(Bpin)] may be involved in the reaction.     

Palladium‐Catalyzed Direct C?H Arylation of Isoxazoles at the 5‐Position

A palladium‐catalyzed direct arylation of isoxazoles with aryl iodides has been achieved. The C H bond at the 5‐position is activated selectively to give coupling products in moderate to good yields. This direct arylation was applied to the synthesis of a spiro‐type chiral ligand, which proved to be most effective to the palladium‐catalyzed tandem cyclization of a dialkenyl alcohol.     

Synthesis of 2‐ and 2,7‐Functionalized Pyrene Derivatives: An Application of Selective C?H Borylation

An efficient synthetic route to 2‐ and 2,7‐substituted pyrenes is described. The regiospecific direct C? H borylation of pyrene with an iridium‐based catalyst, prepared in situ by the reaction of [{Ir(μ‐OMe)cod}₂] (cod=1,5‐cyclooctadiene) with 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine, gives 2,7‐bis(Bpin)pyrene ( 1 ) and 2‐(Bpin)pyrene ( 2 , pin=OCMe₂CMe₂O). From 1 , by simple derivatization strategies, we synthesized 2,7‐bis(R)‐pyrenes with R=BF₃K ( 3 ), Br ( 4 ), OH ( 5 ), B(OH)₂ ( 6 ), and OTf ( 7 ). Using these nominally nucleophilic and electrophilic derivatives as coupling partners in Suzuki–Miyaura, Sonogashira, and Buchwald–Hartwig cross‐coupling reactions, we obtained 2,7‐bis(R)‐pyrenes with R=(4‐CO₂C₈H₁₇)C₆H₄ ( 8 ), Ph ( 9 ), C≡CPh ( 10 ), C≡C[{4‐B(Mes)₂}C₆H₄] ( 11 ), C≡CTMS ( 12 ), C≡C[(4‐NMe₂)C₆H₄] ( 14 ), C≡CH ( 15 ), N(Ph)[(4‐OMe)C₆H₄] ( 16 ), and R=OTf, R′=C≡CTMS ( 13 ). Lithiation of 4 , followed by reaction with CO₂, yielded pyrene‐2,7‐dicarboxylic acid ( 17 ), whilst borylation of 2‐tBu‐pyrene gave 2‐tBu‐7‐Bpin‐pyrene ( 18 ) selectively. By similar routes (including Negishi cross‐coupling reactions), monosubstituted 2‐R‐pyrenes with R=BF₃K ( 19 ), Br ( 20 ), OH ( 21 ), B(OH)₂ ( 22 ), [4‐B(Mes)₂]C₆H₄ ( 23 ), B(Mes)₂ ( 24 ), OTf ( 25 ), C≡CPh ( 26 ), C≡CTMS ( 27 ), (4‐CO₂Me)C₆H₄ ( 28 ), C≡CH ( 29 ), C₃H₆CO₂Me ( 30 ), OC₃H₆CO₂Me ( 31 ), C₃H₆CO₂H ( 32 ), OC₃H₆CO₂H ( 33 ), and O(CH₂)₁₂Br ( 34 ) were obtained from 2 . These derivatives are of synthetic and photophysical interest because they contain donor, acceptor, and conjugated substituents. The crystal structures of compounds 4 , 5 , 7 , 12 , 18 , 19 , 21 , 23 , 26 , and 28 – 31 have also been obtained from single‐crystal X‐ray diffraction data, revealing a diversity of packing modes, which are described in the Supporting Information. A detailed discussion of the structures of 1 and 2 , their polymorphs, solvates, and co‐crystals is reported separately.