Lewis Base Activation of Silyl Acetals: Iridium-Catalyzed Reductive Horner–Wadsworth–Emmons Olefination

Template-Directed Selective Photodimerization Reactions of 5-Arylpenta-2,4-dienoic Acids

We developed an efficient method that enables selective photodimerization of 5-arylpenta-2,4-dienoic acids (i.e., vinylogous cinnamic acids). The use of 1,8-dihydroxynaphthalene as a template ensures proximity of the two reacting olefins so that irradiation of template-bound dienoic acids gives mono [2 + 2] cycloaddition products in good to excellent yields (up to 99%), as single regioisomers, and with high diastereoselectivities (dr = 3:1 to 13:1). The geometrical and stereochemical features of compounds 12a, 16a, and 22a were analyzed by X-ray crystallography.

An enhanced stereoselective synthesis of α,β-unsaturated esters through the Horner-Wadsworth-Emmons reaction in deep eutectic solvents

A new scalable synthesis of (E)-α,β-unsaturated esters has been developed using protic, non-toxic, and biodegradable deep eutectic solvents through the Horner-Wadsworth-Emmons reaction between triethyl phosphonates and (hetero)aromatic carbonyl compounds, encompassing electron-withdrawing and electron-donating groups. Stereoselective preparation of disubstituted or trisubstituted ethyl cinnamate derivatives is achieved in the presence of LiOH, K2CO3, or DBU as bases, at room temperature and under air. Demonstrated with the synthesis of (E)-ethyl 3-(4-bromophenyl)acrylate, the same eutectic mixture (choline chloride/urea) proved to be reusable for three consecutive runs. Gram-scale reactions (10 mmol) can be carried out without the formation of side products, thereby ensuring high atom economy and an EcoScale score of 71.

Iron-Catalyzed Gamma-Gamma Dimerization of Siloxydienes

We report the oxidative dimerization reaction of siloxydienes derived from simple enones that creates a new gamma-gamma (γ-γ) C-C bond using catalytic iron and benzoyl peroxide as the terminal oxidant in acetonitrile solvent at ambient temperature. The reaction shows a broad substrate scope including cyclic and acyclic siloxydienes derived from ketones, aldehydes, and esters, which are converted to 1,8-dicarbonyl compounds under mild catalytic reaction conditions in 19-89 % yield across 30 examples. The method is suitable for the coupling of sterically demanding carbon centers, including the formation of vicinal quaternary centers. Conceptually, the dienol ether serves as a precursor to a conjugated radical cation, which undergoes highly site selective γ-dimerization reactions. The γ-γ dimerization strategy is applied to the synthesis of a bioactive analogue of honokiol.

Partial reductions of carboxylic acids and their derivatives to aldehydes

Recent advances in partial reductions of inert carboxylic acids and their derivatives to active aldehydes are reviewed.

A Concise Total Synthesis of Dehydroantofine and Its Antimalarial Activity against Chloroquine-Resistant Plasmodium falciparum

The total synthesis of dehydroantofine was achieved by employing a novel, regioselective, azahetero Diels-Alder reaction of easily accessible 3,5-dichloro-2H-1,4-oxazin-2-one with 14 a as a key step. Furthermore, it is demonstrated that dehydroantofine is a promising candidate as a new antimalarial agent in a biological assay with chloroquine-resistant Plasmodium falciparum.

Step-Economic Synthesis of Biomimetic β-Ketopolyene Thioesters and Demonstration of Their Usefulness in Enzymatic Biosynthesis Studies

Studies on the biosynthetic processing of polyene thioester intermediates are complicated by limited access to appropriate substrate surrogates. We present a step-economic synthetic access to biomimetic β-ketopolyene thioesters that is based on an Ir-catalyzed reductive Horner-Wadsworth-Emmons olefination. New β-ketotriene and pentaenethioates of pantetheine and N-acetylcysteamine were exemplarily synthesized via short and concise routes. The usefulness of these compounds was demonstrated in an in vitro assay with the ketoreductase domain MycKRB from mycolactone biosynthesis.

Improving Covalent Organic Frameworks Fluorescence by Triethylamine Pinpoint Surgery as Selective Biomarker Sensor for Diabetes Mellitus Diagnosis

The nitrogen-containing imine or hydrazone linked covalent organic frameworks (COFs) are poorly luminescent due to the fluorescence quenching by nitrogen atoms in the linkages, even if highly luminescent units and linkers are employed. The fluorescence quenching pathway to prevent linkage-originated to mitigate the inherent limitations of the linkage is a promising method for luminescent COFs. The generation of N^- by deprotonation of the N-H unit eliminates the electron transfer from N lone pair to COF (TpPa-1) and enhances the luminescence. In this work, TpPa-1 achieved turn-on luminescence response with good sensitivity and reproducibility toward triethylamine (TEA) vapor in the process of deprotonation. The fabricated detector offers a viable approach for sensing ppm-level TEA, which can remind people to take timely measures to reduce the environmental hazards caused by TEA. The fluorescent sensor TpPa-1@LE constructed by the products of TpPa-1 and TEA can quantitatively trace biomarker methylglyoxal (MGO) for diabetes mellitus diagnosis in serum system. Furthermore, using TEA and MGO as input signals and the two fluorescence emissions G476 and Y525 as output signals, an advanced analytical device based on two Boolean logic gates with INH and AND function is constructed. This work provides a new strategy for improving the weak luminescence of COF in aqueous solution and realizes selective response to biomarker (MGO) for diabetes mellitus diagnosis.

Iridium-Catalyzed Reductive Allylation of Esters

The catalytic reductive transformation of carboxylic esters into α-branched ethers is described. The procedure pivots on the chemoselective iridium-catalyzed hydrosilylation of ester and lactone functionality to afford a silyl acetal intermediate. Upon treatment with a Lewis acid, these hemilabile intermediates dissociate to form reactive oxocarbenium ions, which can be intercepted by allyltributyltin nucleophiles, resulting in the formation of valuable α-branched alkyl-alkyl ether derivatives. This reductive allylation procedure was found to be amenable to a range of carboxylic ester starting materials, and good chemoselectivity for ethyl over tert-butyl esters was demonstrated. Furthermore, downstream synthetic manipulation of α-amino acid-derived products led to the efficient formation of pyrrolidine, piperidine, and azepane frameworks.

Access to Chiral HWE Reagents by Rhodium-Catalyzed Asymmetric Arylation of γ,δ-Unsaturated β-Ketophosphonates

Asymmetric arylation of γ,δ-unsaturated β-ketophosphonates with arylboronic acids is reported. By using the ( R)-diene* ligated rhodium(I) chloride complex as a catalyst under none basic conditions, the corresponding β-ketophosphonates bearing a δ-chiral center were obtained in high yields (up to 99%) with good to excellent enantioselectivities (up to >99% ee). The enantioenriched products can be readily converted to diverse chiral β'-aryl enones by the Horner-Wadsworth-Emmons reaction.

Efficient synthesis of ether phosphonates using trichloroacetimidate and acetate coupling methods

A series of ether phosphonates have been prepared by trichloroacetimidate and acetate coupling methods. Trichloroacetimidates or acetates were treated with primary and secondary alcohols as O-nucleophiles in the presence of catalytic TMSOTf to afford 21 examples of diethyl alkyloxy(substitutedphenyl)methyl phosphonates via C–O bond formation in 55–90% yields and short reaction time.

An efficient method for the synthesis of various ether phosphonates by trichloroacetimidate and acetate coupling methods is described.