Nature synthesis最新文献

The palladium-catalysed Suzuki–Miyaura cross-coupling (SMC) is currently the most commonly used reaction to construct carbon–carbon bonds in the pharmaceutical industry. Typical methods require the use of a base, which limits the substrate scope. To mitigate this shortcoming, substantial effort has been made to develop base-tolerant organoboron reagents, efficient catalysts and reaction conditions that do not require external bases. Still, many boronic acids cannot be used or must be independently protected, and many Lewis-basic functional groups poison the catalyst. Here we report a conceptually different SMC reaction that can proceed even under acidic conditions, with a broad substrate scope. Key to this advance is the formation of an acid-stable, palladium-based ion pair between the reaction partners that does not require base for subsequent productive transmetallation. Boronic acids that cannot be used directly in other SMC reactions, such as 2-pyridylboronic acid and boronic acids with strong Lewis bases, can now be used successfully.

Hierarchical assembly is used to construct complex materials using elementary building units, mainly depending on the non-covalent interactions involving dynamic bonds. Here we present a hierarchical assembly strategy to build highly crystalline tubular frameworks. A multi-level assembly process driven by dynamic covalent bonds and coordination bonds is shown to produce a supramolecular nanotubular framework and three tubular covalent organic frameworks (COFs). These materials consist of well-ordered triangular nanotubes assembled in an oriented manner. In tubular COFs, the spacing between adjacent nanotubes can be systematically adjusted by altering the connector lengths to create mesoporous structures with adjustable pore size. Moreover, reversible transformations between tubular COFs and layered COFs were achieved by the reversible addition and removal of Zn(NO₃)₂. The facile demetallation–remetallation process confers tuneable structural properties to the materials and enables the layered COFs to serve as efficient ‘sponges’ for metal ions. This study represents a notable advance in hierarchical assembly; incorporating covalent bonding into this process is expected to greatly accelerate the development of new materials.

Dehydrogenation of an alkyl group via C–H activation forms a vinyl unit, which can act as a versatile stepping stone for diverse late-stage structural modifications at two adjacent sp³ carbon centres. However, enantioselective dehydrogenation via C–H metalation remains a challenge. Here we describe the realization of palladium-catalysed enantioselective β,γ-dehydrogenation of cycloalkyl amides enabled by chiral oxazoline–pyridone ligands to afford a wide range of highly elaborated carbocycles with exceptional enantioselectivity (>99% e.e.). Notably, the resulting chiral β,γ-unsaturated carbocycles are difficult to access via an inverse electron demand Diels–Alder reaction. Through ligand control, a tandem dehydrogenation and C–H olefination sequence also led to the formation of chiral β-alkylidene-γ-lactams. Remarkably, this catalyst is also compatible with biologically important natural products, including diterpenes and pentacyclic triterpenes, where each enantiomer of our chiral ligand enables site-selective modification at four distinct sites within the E ring.