Catalytic Kinetic Resolution of Monohydrosilanes via Rhodium-Catalyzed Enantioselective Intramolecular Hydrosilylation.

The catalytic access of silicon-stereogenic organosilanes remains a big challenge, and largely depends on the desymmetrization of the symmetric precursors with two identical substitutes attached to silicon atom. Here we report the construction of silicon-stereogenic organosilanes via catalytic kinetic resolution of racemic monohydrosilanes with good to excellent selectivity factors. Both Si-stereogenic dihydrobenzosiloles and Si-stereogenic monohydrosilanes could be efficiently accessed in one single operation via Rh-catalyzed enantioselective intramolecular hydrosilylation, employing (R,R)-Et-DuPhos as the optimal ligand. This catalytic protocol features mild conditions, a low catalyst loading (0.1 mol % [Rh(cod)Cl]2), high stereoinduction (S factor up to 152), and excellent scalability. Moreover, further derivatizations led to the efficient synthesis of uncommon middle-size (7- and 8-membered) Si-stereogenic silacycles. Preliminary mechanistic study indicates this reaction might undergo a modified Chalk-Harrod mechanism.

One-Pot Cyclization to Large Peptidomimetic Macrocycles by In Situ-Generated ß-Turn-Enforced Folding.

Macrocycles have been targets of extensive synthetic efforts for decades because of their potent molecular recognition and self-assembly capabilities. Yet, efficient syntheses of macrocyclic molecules via irreversible covalent bonds remain challenging. Here, we report an efficient approach to large peptidomimetic macrocycles by using the in situ-generated ß-turn structural motifs afforded in the amidothiourea moieties from the early steps of the reaction of 2 molecules of bilateral amino acid-based acylhydrazine with 2 molecules of diisothiocyanate. Four chiral and achiral peptidomimetic large macrocycles were successfully synthesized in high yields of 45-63% in a feasible one-pot reaction under sub-molar concentration conditions and were purified by simple filtration. X-ray crystallographic characterization of three macrocycles reveals an important feature that their four ß-turn structures, each maintained by four 10-membered intramolecular hydrogen bonds, alternatively network the four aromatic arms. This affords an interesting conformation switching mode upon anion binding. Binding of SO42- to 1L or 1D that contains 4 alanine residues (with the lowest steric hinderance among the macrocycles) leads to an inside-out structural change of the host macrocycle, as confirmed by the X-ray crystal structure of 1L-SO42- and 1D-SO42- complexes, accompanied by an inversion of the CD signals. On the basis of the strong sulfate affinity of the macrocycles, we succeeded in the removal of sulfate anions from water via a macrocycle-mediated liquid-liquid extraction method. Our synthetic protocol can be easily extended to other macrocycles of varying arms and/or chiral amino acid residues; thus, a variety of structurally and functionally diverse macrocycles are expected to be readily made.

Diverse Synthesis of Alkenylsilanes via Pd-Catalyzed Alkenyl C-H Silylation.

Here, we disclose a general approach for the diverse synthesis of alkenylsilanes in a highly efficient, stereoselective, and atom-economic manner by leveraging the palladium-catalyzed disilylation reaction of 2-bromostyrene derivatives with hexamethyldisilane, which is suitable for the preparation of a series of disubstituted, trisubstituted, and tetrasubstituted alkenylsilanes. Furthermore, the resulting tetrasubstituted alkenylsilanes could be readily transformed into the corresponding diarylated benzosiloles, which have been proven to be a potential AIE material and a fluorene material.

Nickel-Catalyzed Cross-Coupling of Amino-Acid-Derived Alkylzinc Reagents with Alkyl Bromides/Chlorides: Access to Diverse Unnatural Amino Acids.

Unnatural α-amino acids are important synthetic targets in the field of peptide science. Herein we report an efficient, versatile, and straightforward strategy for the synthesis of homophenylalanine derivatives via the nickel-catalyzed Csp3-Csp3 cross-coupling of (fluoro)benzyl bromides/chlorides with natural α-amino-acid-derived alkylzinc reagents. The current protocol features the advantages of a low-cost nickel catalyst system, synthetic convenience, and the tolerance of rich functionality and stereochemistry.

A Class of Multiresponsive Colorimetric and Fluorescent pH Probes via Three Different Reaction Mechanisms of Salen Complexes: A Selective and Accurate pH Measurement.

We report a class of multiresponsive colorimetric and fluorescent pH probes based on three different reaction mechanisms including cation exchange, protonation, and hydrolysis reaction of K(I), Ca(II), Zn(II), Cu(II), Al(III), and Pd(II) Salen complexes. Compared with traditional pure organic pH probes, these complex-based pH probes exhibited a much better selectivity due to the shielding function of the filled-in metal ion in the complex. Their pH sensing performances were affected by the ligand structure and the central metal ion. This work is the first report of "off-on-on'-off" colorimetric and fluorescent pH probes that possess three different reaction mechanisms and should inspire the design of multiple-responsive probes for important analytes in biological systems.