Stereoselective Synthesis of Vinylboronates by Rh‐Catalyzed Borylation of Stereoisomeric Mixtures

The stereoselective preparation of vinylboronates via rhodium‐catalyzed borylation of E/Z mixtures of vinyl actetates is described, and this method was also extended to synthesis of vinyldiboronates. These transformations feature high functional group compatibility and mild reaction conditions. Control experiments support a mechanism that involved a Rh‐catalyzed borylation‐isomerization sequence. The isomerization of (Z)‐vinylboronates to (E)‐isomers was also demonstrated.     

Divergent and Stereoselective Synthesis of Tetraarylethylenes from Vinylboronates

The synthesis of a new tetraborylethylene (TBE) is reported, and its application in the preparation of [4+0]-tetraarylethenes (TAEs) is elucidated. TAEs have widespread applications in material science and supramolecular chemistry due to their aggregation-induced emission (AIE) properties. The divergent and stereoselective synthesis of [3+1]-, [2+2]-, and [2+1+1]-TAEs via multiple couplings of vinylboronates with aryl bromides is demonstrated. These couplings feature a broad substrate scope and excellent functional group compatibility due to mild reaction conditions. Facile access to various tetraarylethenes is provided. This strategy represents an important complement to the conventional methods employed for the synthesis of TAEs, and would be a valuable tool for synthesizing TAE-based molecules useful in functional materials, biological imaging and chemical sensing.     

Highly Diastereoselective Synthesis of Syn‐1,3‐Dihydroxyketone Motifs from Propargylic Alcohols via Spiroepoxide Intermediates

Syn dihydroxyketone motifs are embedded in a wide range of biologically active natural products, however the development of stereoselective synthetic methods to assemble these structures has proven a challenging task. We report a highly diastereoselective method for the synthesis of syn dihydroxyketones from propargylic alcohols, with wide scope for application in natural product synthesis. The reaction sequence involves regioselective cyclisation of propargylic alcohols with incorporation of a triketone to give enol dioxolanes that are then diastereoselectively epoxidised to form unusual spiroepoxide intermediates. Hydrolysis affords syn dihydroxyketones as essentially single diastereisomers. The reaction sequence is operationally simple, of wide substrate scope, and remarkably can be efficiently carried out as a one‐pot process with no loss of overall yield or diastereoselectivity.     

（E）-α-Bromovinylselenides as Convenient Precursors for Stereose-lective Synthesis of Trisubstituted Alkenes

Based on the different reactivity of selanyl and bromo groups,(E)-α-bromovinylselenides can undergo sequential cross coupling reactions with nucleophiles in the presence of transition metal complexes to form two carbon-carbon bonds in the same olefinic carbon leading to trisubstituted alkenes stereoselectively in good yields.     

Guanidine–Copper Complex Catalyzed Allylic Borylation for the Enantioconvergent Synthesis of Tertiary Cyclic Allylboronates

An enantioconvergent synthesis of chiral cyclic allylboronates from racemic allylic bromides was achieved by using a guanidine–copper catalyst. The allylboronates were obtained with high γ/α regioselectivities (up to 99:1) and enantioselectivities (up to 99 % ee), and could be further transformed into diverse functionalized allylic compounds without erosion of optical purity. Experimental and DFT mechanistic studies support an S_N2′ borylation process catalyzed by a monodentate guanidine–copper(I) complex that proceeds through a special direct enantioconvergent transformation mechanism.     

First Example of Highly Stereoselective Synthesis of 1,2,3‐Trisubstituted Cyclopropanes via Chiral Selenonium Ylides

A new strategy for the highly stereoselective synthesis of three stereoisomers of chiral 1,2,3‐trisubstituted cyclopropanes in good yields with excellent diastereoselectivities and very high enantioselectivities (up to >99 % ee) was developed via selenonium ylides (see scheme). Possible pathways for the asymmetric cyclopropanations were also proposed.

     

One‐Step Borylation of 1,3‐Diaryloxybenzenes Towards Efficient Materials for Organic Light‐Emitting Diodes

The development of a one‐step borylation of 1,3‐diaryloxybenzenes, yielding novel boron‐containing polycyclic aromatic compounds, is reported. The resulting boron‐containing compounds possess high singlet‐triplet excitation energies as a result of localized frontier molecular orbitals induced by boron and oxygen. Using these compounds as a host material, we successfully prepared phosphorescent organic light‐emitting diodes exhibiting high efficiency and adequate lifetimes. Moreover, using the present one‐step borylation, we succeeded in the synthesis of an efficient, thermally activated delayed fluorescence emitter and boron‐fused benzo[6]helicene.     

Stereoselective Solvent‐Free Synthesis of 4‐Hydroxy‐1,3‐thiazinane‐2‐thiones

An efficient solvent‐free one‐pot stereoselective synthesis of 4‐hydroxy‐1,3‐thiazinane‐2‐thione derivatives from the reaction of primary amines and carbon disulfide in the presence of α,β‐unsaturated aldehydes has been reported. The 4‐hydroxy‐1,3‐thiazinane‐2‐thione derivatives were easily converted to the related dehydrated or acetylated products.     

Lithium Enolates: ‘Capricious’ Structures – Reliable Reagents for Synthesis

The first part of this review article deals with the structures of enolates. The development of research in this field during the last half century will be illustrated by highlightening seminal contributions, while, by no means, an attempt of comprehensiveness is made: the choice of spotlights has, admittedly, a personal touch. Aside from derivatization of lithium enolates and their crystal structures that meanwhile are classics, more recent solution studies are presented. In the second part, it will be shown by contributions of our laboratory that, despite their complicated structures, lithium enolates are reliable ‘workhorses’ in synthesis with emphasis being given to stereoselective C? C bond forming reactions due to the Pd‐catalyzed allylic alkylation of non‐stabilized, preformed enolates.     

Acid‐Induced Rearrangement of Cycloadducts from Cyclopropenecarboxylates and 1,3‐Diarylisobenzofurans

Treatment of several Diels–Alder adducts of cyclopropenecarboxylates and 1,3‐diarylisobenzofurans with a strong acid triggers a skeletal rearrangement resulting in 4,8b‐dihydro‐3aH‐indeno[1,2‐b]furans.     

Asymmetric Synthesis of 2,4,5‐Trisubstituted Δ2‐Thiazolines

Δ²‐Thiazolines are interesting heterocycles that display a wide variety of biological characteristics. They are also common in chiral ligands used for asymmetric syntheses and as synthetic intermediates. Herein, we present asymmetric routes to 2,4,5‐trisubstituted Δ²‐thiazolines. These Δ²‐thiazolines were synthesized from readily accessible/commercially available α,β‐unsaturated methyl esters through a Sharpless asymmetric dihydroxylation and an O→N acyl migration reaction as key steps. The final products were obtained in good yields with up to 97 % enantiomeric excess.     

One‐Pot Sequential Organocatalysis: Highly Stereoselective Synthesis of Trisubstituted Cyclohexanols

A highly diastereoselective (d.r. >99:1) and enantioselective (ee value up to 96 %) synthesis of trisubstituted cyclohexanols was achieved by using a one‐pot sequential organocatalysis that involved a quinidine thiourea‐catalyzed tandem Henry–Michael reaction between nitromethane and 7‐oxo‐hept‐5‐en‐1‐als followed by a tetramethyl guanidine (TMG)‐catalyzed tandem retro‐Henry–Henry reaction on the reaction products of the tandem Henry–Michael reaction. Through a mechanistic study, it has also been demonstrated that similar results may also be achieved with this one‐pot sequential organocatalysis by using the racemic Henry product as the substrate.