Catalytic atroposelective synthesis of axially chiral benzonitriles via chirality control during bond dissociation and CN group formation

The applications of axially chiral benzonitriles and their derivatives remain mostly unexplored due to their synthetic difficulties. Here we disclose an unusual strategy for atroposelective access to benzonitriles via formation of the nitrile unit on biaryl scaffolds pre-installed with stereogenic axes in racemic forms. Our method starts with racemic 2-arylbenzaldehydes and sulfonamides as the substrates and N-heterocyclic carbenes as the organocatalysts to afford axially chiral benzonitriles in good to excellent yields and enantioselectivities. DFT calculations suggest that the loss of p-toluenesulfinate group is both the rate-determining and stereo-determining step. The axial chirality is controlled during the bond dissociation and CN group formation. The reaction features a dynamic kinetic resolution process modulated by both covalent and non-covalent catalytic interactions. The axially chiral benzonitriles from our method can be easily converted to a large set of functional molecules that show promising catalytic activities for chemical syntheses and anti-bacterial activities for plant protections.

Grignard reagent formation via C-F bond activation: a centenary perspective

Examples of Grignard reagents obtained by C-F bond activation with magnesium kept appearing in the literature over the last century. Due to the high bond dissociation energy of the C-F...

Dynamics of methyl radical formation by 266 nm photolysis of xylenes and mesitylene

The 266 nm photodissociation of three xylene isomers and mesitylene leading to the formation of methyl radical was examined. The kinetic energy release profiles for the methyl radical were almost identical for all the three isomers of xylene and mesitylene, while substantial differences were observed for the corresponding profiles of the co-fragment produced by loss of one methyl group. This observation be attributed to the formation of the methyl radical from alternate channels. The total kinetic energy distribution profiles were rationalized based on the dissociation of {sp2}C–C{sp3} bond in the cationic state, wherein the {sp2}C–C{sp3} bond dissociation energy is lowered relative to the ground state. The dissocaiton in the cationic state follows a resonant three-photon absorption process, resulting in maximum total kinetic energy of about 1.6 – 1.8 eV for the photofragments. A results in. Fitting of the TKER distribution profiles to empirical function reveals that the dynamics of {sp2}C–C{sp3} bond dissociation is insensitive to the position of substitution but marginally dependent on the number of methyl groups.

Photodissociation of dicarbon: How nature breaks an unusual multiple bond

The dicarbon molecule (C2) is found in flames, comets, stars, and the diffuse interstellar medium. In comets, it is responsible for the green color of the coma, but it is not found in the tail. It has long been held to photodissociate in sunlight with a lifetime precluding observation in the tail, but the mechanism was not known. Here we directly observe photodissociation of C2. From the speed of the recoiling carbon atoms, a bond dissociation energy of 602.804(29) kJ·mol−1 is determined, with an uncertainty comparable to its more experimentally accessible N2 and O2 counterparts. The value is within 0.03 kJ·mol−1 of high-level quantum theory. This work shows that, to break the quadruple bond of C2 using sunlight, the molecule must absorb two photons and undergo two “forbidden” transitions.