Ke-Fang Yang

Modulation of Silver–Titania Nanoparticles on Polymethylhydrosiloxane‐based Semi‐Interpenetrating Networks for Catalytic Alkynylation of Trifluoromethyl Ketones and Aromatic Aldehydes in Water

In this work, we have developed a new approach to monodispersed hybrid Ag@TiO2 nanocomposites using a titanium‐promoted cross‐linking reduction in the SiH functional material, polymethylhydrosiloxane (PMHS)‐based semi‐interpenetrating networks (PMHSIPN). The titania was designed to be highly dispersed on the functional material and then the Ag@TiO2 nanoparticles were formed in uniform size and shape under mild conditions. The experimental results reveal that the nanosilver catalysts (the fabricated Ag@TiO2 located on the PMHSIPNs, namely, nanoAg@TiO2@PMHSIPN) have enhanced catalytic activities in the alkynylation of trifluoromethyl ketones or α,β‐unsaturated trifluoromethyl ketones with terminal alkynes. In this reaction, the hybrid Ag@TiO2 nanoparticles exhibited a high level of catalytic activity for the selective 1,2‐alkynylation of various trifluoromethyl ketones and α,β‐unsaturated trifluoromethyl ketones into a wide range of fluorinated alcohols in water. Finally, on the basis of the nanoAg@TiO2@PMHSIPN‐catalyzed alkynylation of trifluoromethyl ketones, we developed a new concept whereby highly reactive substrates act as a “reactive tractor” or “reactive springboard” to drive the transformation of poorly reactive substrates as springboard chemistry. Consequently, we found that trifluoromethyl ketone can be used as an efficient additive in the nanosilver‐catalyzed alkynylation of aldehydes.

Copper-Catalyzed Huisgen and Oxidative Huisgen Coupling Reactions Controlled by Polysiloxane-Supported Amines (AFPs) for the Divergent Synthesis of Triazoles and Bistriazoles

An interesting example of a divergent catalysis with a copper(I) and amine-functional macromolecular polysiloxanes system was successfully presented in click chemistry. In this manuscript, we demonstrate the remarkable ability of the secondary amine-functional polysiloxane to induce oxidative coupling in the copper-mediated Huisgen reactions of azides and alkynes, thereby achieving good yields and selectivities. The click reactions mediated by a polysiloxane-supported secondary amine allow the preparation of novel heterocyclic compounds, that is, bistriazoles. Comparably, it is also surprising that the use of a diamine-functional polysiloxane as ligand led to a classic Huisgen [3+2] cycloaddition in excellent yields. From the results of the present amine-functional polysiloxanes-controlled Huisgen reaction or oxidative Huisgen coupling reaction to divergent products and the proposed mechanism, we suggested that the mononuclear bistriazole-copper complex stabilized and dispersed by the secondary amine-functional polysiloxane was beneficial to prevalent the way to oxidative coupling.

Development of a Novel Multifunctional N,P Ligand for Highly Enantioselective Palladium‐Catalyzed Asymmetric Allylic Etherification of Alcohols and Silanols

CycloN2P2-Phos! The use of the multidentate phosphine, CycloN2P2-Phos, which contains four heteroatoms (two nitrogen and two phosphorus atoms), in the palladium-catalyzed asymmetric allylic etherification (AAE) of alcohols and silanols leads to excellent levels of enantioselectivity (up to 99 % ee).

Dehydrogenation and oxidative coupling of alcohol and amines catalyzed by organosilicon-supported TiO2@PMHSIPN

The catalytic dehydrogenation and tandem transformation of aromatic alcohols, including oxidative coupling of alcohols and amines, were achieved successfully using a catalytic amount of organosilicon-supported titania (TiO2@PMHSIPN), which enables the efficient synthesis of aromatic aldehydes, imines, and benzimidazoles in good to excellent yields.

Probing the evolution of an Ar-BINMOL-derived salen–Co(III) complex for asymmetric Henry reactions of aromatic aldehydes: salan–Cu(II) versus salen–Co(III) catalysis

A new type of chiral salen–Co catalyst that features aromatic π-walls and an active Co(III) center has been developed for enantioselective Henry/nitroaldol reactions on the basis of salen–Cu catalysis. The asymmetric Henry reaction of aromatic aldehydes and nitromethane catalyzed by an Ar-BINMOL-derived salen–Co(III) complex was achieved with high yields (up to 93%) and excellent enantioselectivities (up to 98% ee). And more interestingly, it was supposed that either salan–Cu(II) or salen–Co(III) complex-catalyzed Henry reaction was an ideal model reaction for providing direct evidence of noncovalent interaction due to the distinguishable ortho-substituted aromatic aldehydes from meta- or para-substituted benzaldehydes in terms of enantioselectivities and yields.

Organocatalytic aza-Michael/retro-aza-Michael reaction: pronounced chirality amplification in aza-Michael reaction and racemization via retro-aza-Michael reaction.

A detailed experimental investigation of an aza-Michael reaction of aniline and chalcone is presented. A series of Cinchona alkaloid-derived organocatalysts with different functional groups were prepared and used in the aza-Michael and retro-aza-Michael reaction. There was an interesting finding that a complete reversal of stereoselectivity when a benzoyl group was introduced to the cinchonine and cinchonidine. The chirality amplification vs. time proceeds in the quinine-derived organocatalyst containing silicon-based bulky group, QN-TBS, -catalyzed aza-Michael reaction under solvent-free conditions. In addition, we have demonstrated for the first time that racemization was occurred in suitable solvents under mild conditions due to retro-aza-Michael reaction of the Michael adduct of aniline with chalcone. These indicate the equilibrium of retro-aza-Michael reaction and aza-Michael reaction produce the happening of chirality amplification in aza-Michael reaction and racemization via retro-aza-Michael reaction under different conditions, which would be beneficial to the development of novel chiral catalysts for the aza-Michael reactions.

One-by-one hydrogenation, cross-coupling reaction, and Knoevenagel condensations catalyzed by PdCl2 and the downstream palladium residue

A novel catalyst-economic strategy with a recovered palladium catalyst was successfully applied for multi-task and maximum reuse in different types of one-by-one downstream reactions, from catalytic hydrogenation to Suzuki and Sonogashira-type cross-coupling reactions, Knoevenagel condensations, and trans-Knoevenagel-like condensations.

DMSO as oxidant and sulfenylating agent for metal-free oxidation and methylthiolation of alcohol-containing indoles

A simple and efficient methylthiolation protocol was successfully established for the synthesis of ketone-substituted indoles bearing 3-methylthioether moiety. The new synthetic approach featured metal-free oxidation and methylthiolation of alcohol-containing indoles, in which new C–S bond and CO bond were formed simultaneously using dimethyl sulfoxide as the sulfur source under the Swern oxidation conditions. The methylthiolation reaction provides a simple and facile procedure to methylthiolated indoles from readily available starting materials in good yields.

Enantioselective cyanosilylation of aldehydes catalyzed by a multistereogenic salen–Mn(III) complex with a rotatable benzylic group as a helping hand

A multistereogenic salen–Mn(III) complex bearing an aromatic pocket and two benzylic groups as helping hands was found to be efficient in the catalysis of asymmetric cyanosilylation. The salen–Mn catalyst partially mimics the functions of biocatalysts by reasonably utilizing the steric and electronic properties of the catalytic center to interact with the substrate.

Palladium-catalyzed Si–C bond-forming silylation of aryl iodides with hydrosilanes: an enhanced enantioselective synthesis of silicon-stereogenic silanes by desymmetrization

An enantioselective Pd-catalyzed silicon–carbon bond-forming silylation reaction of aryl iodides with hydrosilanes for the synthesis of silicon-stereogenic silanes has been developed, in which a systematic optimization of a TADDOL-derived monodentate phosphoramidite ligand set resulted in the identification of a new TADDOL-derived phosphoramidite ligand that accesses chiral silanes with moderate to good yield and enantioselectivity under mild conditions.