“
“A bistable donor-acceptor [2]catenane, which is composed of a crown ether containing a hydroquinone unit and a 1,5-diaminonaphthalene unit, interlocked mechanically by cyclobis(paraquat-p-phenylene) as its tetrachloride, see more exists as a mixture of translational isomers, both in the solid state and in aqueous solution. UV/vis and H-1 NMR spectroscopies demonstrate that this isomeric mixture can be switched in water in the presence of hydrochloric acid to afford a single diprotonated derivative in which only the hydroquinone unit resides inside the cavity of the tetracationic cyclophane. Treatment with 1,4-diazabicyclo[2.2.2]octane resets the molecular switch.”
“In
recent years, carbon-hydrogen bond functionalization has evolved from an organometallic curiosity to a tool used in mainstream applications in the synthesis of complex natural products and drugs. The use of C-H bonds as a transformable functional group is advantageous because these bonds are the most abundant functionality in organic molecules. One-step conversion of these bonds to the desired functionality
shortens synthetic pathways, saving reagents, solvents, and labor. Less chemical waste LY3039478 is generated as well, showing that this chemistry is environmentally beneficial. This Account describes the development and use of bidentate, monoanionic auxiliaries for transition-metal-catalyzed C-H bond functionalization reactions. The chemistry was initially developed to overcome the limitations with palladium-catalyzed C-H bond functionalization assisted by monodentate directing groups. By the use of electron-rich bidentate directing groups, functionalization of unactivated sp(3) C-H bonds under palladium catalysis has been developed. Furthermore, a number of abundant base-metal complexes catalyze functionalization of sp(2) C-H bonds. At this point, aminoquinoline, picolinic acid, and related compounds are among the most used and versatile directing moieties in C-H bond functionalization chemistry. These groups facilitate catalytic functionalization of sp(2) and sp(3) C-H bonds
by iron, cobalt, nickel, copper, ruthenium, rhodium, and palladium complexes. Exceptionally general reactivity is observed, enabling, among JQ-EZ-05 datasheet other transformations, direct arylation, alkylation, fluorination, sulfenylation, amination, etherification, carbonylation, and alkenylation of carbon-hydrogen bonds. The versatility of these auxilaries can be attributed to the following factors. First, they are capable of stabilizing high oxidation states of transition metals, thereby facilitating the C-H bond functionalization step. Second, the directing groups can be removed, enabling their use in synthesis and functionalization of natural products and medicinally relevant substances. While the development of these directing groups presents a significant advance, several limitations of this methodology are apparent.