RESUMEN
The direct carboxylation of the benzylic C-H bonds under mild conditions is of great importance and is quite challenging. Herein, we report an approach for the carboxylation of remote benzylic C(sp3)-H bonds by integrating the redox-neutral visible-light photoredox catalysis and the nitrogen-centered 1,5-hydrogen atom transfer. The chemical transformation progresses via consecutive single electron transfer, 1,5-hydrogen atom transfer, formation of benzylic carbanion, and nucleophilic attack on the CO2 steps, thereby enabling access to the desired carboxylation products with moderate to high yields. We also endeavor to recover the CO2 groups generated in situ intramolecularly to achieve carboxylation under a nitrogen atmosphere, resulting in moderate yields of corresponding carboxylation.
RESUMEN
We describe here an operationally simple and straightforward synthesis method for a series of diverse 4,5-disubstituted 1,2,3-thiadiazoles via the nucleophilic addition of α-diazo carbonyl compounds to carbon disulfide. This method features using abundant and inexpensive carbon disulfide under mild reaction conditions.
RESUMEN
The borylation of unreactive carbon-hydrogen bonds is a valuable method for transforming feedstock chemicals into versatile building blocks. Here, we describe a transition metal-free method for the photoredox-catalyzed borylation of unactivated C(sp3)-H bond, initiated by 1,5-hydrogen atom transfer (HAT). The remote borylation was directed by 1,5-HAT of the amidyl radical, which was generated by photocatalytic reduction of hydroxamic acid derivatives. The method accommodates substrates with primary, secondary and tertiary C(sp3)-H bonds, yielding moderate to good product yields (up to 92%) with tolerance for various functional groups. Mechanistic studies, including radical clock experiments and DFT calculations, provided detailed insight into the 1,5-HAT borylation process.
RESUMEN
We report operationally simple and neutral conditions for borylation of alkyl bromides and iodides to alkyl boronic esters under transition metal- and light-free conditions. A series of substrates with a wide range of functional groups were effectively transformed into the borylation products in moderate to good yields. Mechanistic studies, including radical clock experiments and DFT calculations, gave detailed insight into the radical borylation process.
RESUMEN
Carbon dioxide is a nontoxic, renewable, and abundant C1 source, whereas C-H bond functionalization represents one of the most important approaches to the construction of carbon-carbon bonds and carbon-heteroatom bonds in an atom- and step-economical manner. Combining the chemical transformation of CO2 with C-H bond functionalization is of great importance in the synthesis of carboxylic acids and their derivatives. The contents of this Review are organized according to the type of C-H bond involved in carboxylation. The primary types of C-H bonds are as follows: C(sp)-H bonds of terminal alkynes, C(sp2 )-H bonds of (hetero)arenes, vinylic C(sp2 )-H bonds, the ipso-C(sp2 )-H bonds of the diazo group, aldehyde C(sp2 )-H bonds, α-C(sp3 )-H bonds of the carbonyl group, γ-C(sp3 )-H bonds of the carbonyl group, C(sp3 )-H bonds adjacent to nitrogen atoms, C(sp3 )-H bonds of o-alkyl phenyl ketones, allylic C(sp3 )-H bonds, C(sp3 )-H bonds of methane, and C(sp3 )-H bonds of halogenated aliphatic hydrocarbons. In addition, multicomponent reactions, tandem reactions, and key theoretical studies related to the carboxylation of C-H bonds are briefly summarized. Transition-metal-free, organocatalytic, electrochemical, and light-driven methods are highlighted.
RESUMEN
We describe an operationally simple transition-metal-free borylation of alkyl iodides. This method uses commercially available diboron reagents as the boron source and exhibits excellent functional group compatibility. Furthermore, a diverse range of primary and secondary alkyl iodides could be effectively transformed to the corresponding alkylboronates in excellent yield. Mechanistic investigations suggest that this borylation reaction proceeds through a single-electron transfer mechanism featuring the generation of an alkyl radical intermediate.
RESUMEN
Herein we report a general electrochemical strategy for the Sandmeyer reaction. Using electricity as the driving force, this protocol employs a simple and inexpensive halogen source, such as NBS, CBrCl3, CH2I2, CCl4, LiCl and NaBr for the halogenation of aryl diazonium salts. In addition, we found that these electrochemical reactions could be performed using anilines as the starting material in a one-pot fashion. Furthermore, the practicality of this process was demonstrated in the multigram scale synthesis of aryl halides using highly inexpensive graphite as the electrode. A series of detailed mechanism studies have been performed, including radical clock and radical scavenger study, cyclic voltammetry analysis and in situ electron paramagnetic resonance (EPR) analysis.