We report herein a simple, metal- and additive-free, photoinduced borylation of haloarenes, including electron-rich fluoroarenes, as well as arylammonium salts directly to boronic acids. This ...borylation method has a broad scope and functional group tolerance. We show that it can be further extended to boronic esters and carried out on gram scale as well as under flow conditions.
Boronic acids are centrally important functional motifs and synthetic precursors. Visible light-induced borylation may provide access to structurally diverse boronates, but a broadly efficient ...photocatalytic borylation method that can effect borylation of a wide range of substrates, including strong C–O bonds, remains elusive. Herein, we report a general, metal-free visible light-induced photocatalytic borylation platform that enables borylation of electron-rich derivatives of phenols and anilines, chloroarenes, as well as other haloarenes. The reaction exhibits excellent functional group tolerance, as demonstrated by the borylation of a range of structurally complex substrates. Remarkably, the reaction is catalyzed by phenothiazine, a simple organic photocatalyst with MW < 200 that mediates the previously unachievable visible light-induced single electron reduction of phenol derivatives with reduction potentials as negative as approximately – 3 V versus SCE by a proton-coupled electron transfer mechanism. Mechanistic studies point to the crucial role of the photocatalyst–base interaction.
The development of efficient and selective C−N bond‐forming reactions from abundant feedstock chemicals remains a central theme in organic chemistry owing to the key roles of amines in synthesis, ...drug discovery, and materials science. Herein, we present a dual catalytic system for the N‐alkylation of diverse aromatic carbocyclic and heterocyclic amines directly with carboxylic acids, by‐passing their preactivation as redox‐active esters. The reaction, which is enabled by visible‐light‐driven, acridine‐catalyzed decarboxylation, provides access to N‐alkylated secondary and tertiary anilines and N‐heterocycles. Additional examples, including double alkylation, the installation of metabolically robust deuterated methyl groups, and tandem ring formation, further demonstrate the potential of the direct decarboxylative alkylation (DDA) reaction.
No beating about the bush: (Hetero)aromatic amines underwent decarboxylative N‐alkylation directly with carboxylic acids with a dual copper/acridine photocatalytic system. The directional character of the acridine photocatalysis facilitates the challenging decarboxylation of unactivated carboxylic acids in the presence of more readily oxidizable anilines, thus enabling the use of a wide range of structurally diverse amine and acid substrates (see scheme).
We report herein a simple, additive- and metal-free, photoinduced, dual C–H/C–X borylation of chloro-, bromo-, and iodoarenes. The reaction produces 1,2- and 1,3-diborylarenes on gram scales under ...batch and continuous flow conditions. The regioselectivity of the dual C–H/C–X borylation is determined by the solvent and the substituents in the parent haloarenes.
Treatment of FeCl2(thf)1.5 with the sodium salt of bis(dicyclohexylphosphinomethyl)pyrrole (NaCyPNP) in the presence of pyridine (py) affords the high-spin, five-coordinate iron(II) complex ...FeCl(py)(CyPNP). The chloride complex serves as a starting point for a variety of organometallic iron(II) compounds including S = 1 square planar alkyls, FeR(CyPNP) (R = Me, Et, Bn, Ph). Treatment of FeCl(py)(CyPNP) with NaBEt3H does not generate an analogous square-planar hydride complex, but rather a bimetallic high-spin iron(II) species containing bridging hydride ligands. Analogous transmetalation reactions in the presence of carbon monoxide produced six-coordinate low-spin species FeR(CO)2(CyPNP) (R = Et, Ph, and H). Reduction of FeCl(py)(CyPNP) under CO afforded the low-spin iron(I) carbonyl complex Fe(CO)2(CyPNP). This species could be further reduced with KC8 to afford the anionic iron(0) complex KFe(CO)2(CyPNP)·thf. The breadth of coordination numbers, spin states, and valencies supported by this pyrrole-based PNP ligand demonstrates the flexibility afforded by this pincer framework.
A diaminotriazine-decorated porphyrin-based microporous hydrogen-bonded organic framework has been successfully prepared and characterized using single crystal X-ray diffraction analysis. Its ...activated phase exhibits permanent porosity, gas separation, and proton conductivity under humid conditions.
The Co(I) complex, Co(N2)(CyPNP) (CyPNP = anion of 2,5-bis-(dicyclohexylphosphinomethyl)pyrrole), is active toward the catalytic hydrogenation of terminal alkenes and the semi-hydrogenation of ...internal alkynes under 2 bar of H2 (g) at room temperature. The products of alkyne semi-hydrogenation are a mixture of E- and Z-alkenes. By contrast, use of the related cobalt(I) precatalyst, Co(PMe3)(CyPNP), results in formation of exclusively Z-alkenes. A semi-stable Co(II) species, CoH(CyPNP), can also be generated by treatment of degassed solutions of Co(N2)(CyPNP) with H2. The CoII-hydride displays activity toward both alkene hydrogenation and isomerization, but its instability hampers implementation as a catalyst. Several species relevant to potential catalytic intermediates have been isolated and detected in solution. These compounds include alkene and alkyne adducts of Co(I) as well as a Co(III) dihydride species. Catalytic results with the compounds examined are most consistent with a process involving shuttling between Co(I) and Co(III) states. However, generation of small quantities of Co(II) during catalytic turnover appears to be responsible for the isomerization observed for alkyne semi-hydrogenation. The interplay of cobalt oxidation states within the same catalyst system is discussed in the context of mechanistic scenarios for catalytic hydrogenation.
Conjugated dienes and polyenes are typically synthesized by sequential introduction of CC bonds. Here, we report a practical and scalable, catalytic dienylation that is highly regio- and ...stereoselective for both CC bonds. The reaction is enabled by a stereoselective palladium-catalyzed cross-coupling that is preceded by a regioselective base-induced ring opening of readily available sulfolenes. The dienylation reaction is particularly useful for the synthesis of synthetically challenging dienes containing cis double bonds. We also show that the reaction can serve as a synthetic platform for the construction of conjugated polyenes.
Direct conversion of renewable biomass and bioderived chemicals to valuable synthetic intermediates for organic synthesis and materials science applications by means of mild and chemoselective ...catalytic methods has largely remained elusive. Development of artificial catalytic systems that are compatible with enzymatic reactions provides a synergistic solution to this enduring challenge by leveraging previously unachievable reactivity and selectivity modes. We report herein a dual catalytic dehydrodecarboxylation reaction that is enabled by a crossover of the photoinduced acridine-catalyzed O–H hydrogen atom transfer (HAT) and cobaloxime-catalyzed C–H-HAT processes. The reaction produces a variety of alkenes from readily available carboxylic acids. The reaction can be embedded in a scalable triple-catalytic cooperative chemoenzymatic lipase–acridine–cobaloxime process that allows for direct conversion of plant oils and biomass to long-chain terminal alkenes, precursors to bioderived polymers.
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