A metal-free defluoroborylation of 3,3-difluoropropenes has been developed. The reaction involves the convenient borylation agent B₂pin₂ and a combination of both TBAF and HMDS as an activating system. The fluorinated allylboronates were used as a platform to prepare functionalized monofluoroalkenes.

Abstract

The defluorinative functionalization of allylic fluorides represents an attractive approach for the preparation of molecules containing a monofluoroalkene core. In that sense, introducing a “boryl nucleophile” is a powerful strategy to obtain polyvalent borylated intermediates as versatile synthetic precursors. To perform this reaction without the use of transition metals, the nucleophilic character of a diborane/fluoride system was exploited in a S_N2′ type-substitution reaction of gem-difluoropropenes to install a pinacolborane group. The use of HMDS as a silylated additive is necessary to improve the reactivity. A direct oxidation of the intermediate boronates allowed the isolation of the corresponding β-fluoroallyl alcohols in low to good yields (9–81 %). Other synthetic transformations of a (2-fluoroallyl)boronate are also illustrated.

Inherent chirality represents a distinct form of molecular chirality that does not fit into the four traditional types of molecular chiral elements, which has been observed in a diverse range of molecular structures. This review summarizes the recent advances in the catalytic enantioselective synthesis of inherently chiral molecules, including chiral calixarenes, saddle-shaped chiral cycles, mechanically planar chiral rotaxanes and others.

Abstract

Inherent chirality represents a distinct category of molecular chirality that does not fall within the traditional classification of four chiral elements: central, axial, planar, and helical chirality. While extensive research has been conducted on the catalytic enantioselective construction of these conventional chiralities, the corresponding synthesis of inherently chiral molecules has remained largely unexplored. This minireview provides a comprehensive summary of recent advancements in this field, focusing on the catalytic asymmetric synthesis of inherently chiral calixarenes, saddle-shaped tetraphenylenes and their heterocycle derivatives, mechanically planar chiral rotaxanes and chiral multilayer 3D frameworks, as well as our perspective in this field.

This Review focuses on the very recent advances (from 2021 to the beginning of 2023) in the field of three-component reactions of quinoxalin-2(1H)-ones at the C3 position. According to the kind of radical types involved, some representative examples and detailed reaction mechanism have been categorized and discussed.

Abstract

The multicomponent reactions of quinoxalin-2(1H)-ones has attracted considerable interest due to their significant biological and chemical activities. The very recent advances (from 2021 to the beginning of 2023) on the radical three-component cascade reaction of quinoxalin-2(1H)-one derivatives at the C3 position were summarized in this mini-review. According to the kind of radical types involved, some representative examples and detailed reaction mechanism have been categorized and discussed.

The red front was covered by Figure 1.

This Concept article summarises recent advances in approaches to the synthesis of important vinyl stannane building blocks in a stereocontrolled and regiocontrolled manner. Particular emphasis is put on those routes in which judicious choice of ligand affords a switchable reaction, providing routes to stereodefined olefins from a single starting material.

Abstract

Organostannanes have represented one of the most widely applied reagents in modern cross-coupling chemistry and represent a key reagent in the synthesis of a range of pharmaceutically relevant scaffolds. This Concept article reviews recent advances in approaches to the synthesis of these building blocks in a stereocontrolled and regiocontrolled manner. Particular focus is paid to methods which allow for divergent synthesis of alkenylstannanes and developments in methods which present opportunities for sustainable synthesis.

A PNP pincer manganese complex was applied as catalyst for transfer hydrogenation of quinolines with ammonia borane as hydrogen source. 1,2,3,4-Tetrahydroquinolines were obtained under mild conditions with good to excellent yields. 1,2-Dihydroquinolines were detected by ¹H NMR in the progress and isotopic labelling experiments were performed to determine the destination of ammonia-borane hydrogen atoms.

Abstract

Herein, an efficient methodology for the homogeneous manganese-catalysed transfer hydrogenation of N-heterocycles by using ammonia-borane as a hydrogen source under mild reaction conditions is reported. Good to excellent isolated yields are achieved by applying a PNP manganese pincer complex. In the reaction, 1,2-dihydroquinoline is detected as intermediate by NMR spectra analysis and deuterium labelling experiment. The catalytic reaction likely proceeded by an outer-sphere pathway based on the bifunctional pincer complex.

Herein, we designed and synthesized a range of multi-functional chalcone-based quinolinium salts and their synthetic application in the rapid and straightforward construction of oxa-bridged quinobenzazepine polycycles was successfully explored.

Abstract

Quinobenzazepines are useful in medicinal chemistry, but their synthesis is very challenging. Herein, we designed and synthesized a range of multi-functional chalcone-based quinolinium salts; their synthetic application in the rapid and straightforward construction of quinobenzazepines was successfully explored. A wide range of oxa-bridged quinobenzazepine polycycles were afforded serendipitously through a dearomative cascade reaction of our newly developed quinolinium salts and acetylacetone. This synthetic strategy features high bond- and ring-forming efficiency and complete regio- and diastereoselective control.

The borrowing hydrogen approach allows the direct utilization of non-activated alcohols as alkylating agents. A readily available, air and moisture stable ruthenium complex proves to be a particularly effective hydrogen autotransfer catalyst for the alkylation of various indoles or ketones with poorly reactive alcohols.

Abstract

A diaminocyclopentadienone ruthenium complex has proven to be a highly effective catalyst for the alkylation of indoles or ketones with poorly reactive alcohols. The catalyst is readily available, air and moisture stable and exhibits wide functional group tolerance. The environmentally benign procedure follows a borrowing hydrogen mechanism and requires no excess of either component. Various indoles and ketones are selectively monoalkylated in high yield.

A copper-catalyzed α,β-regioselective (2+4) cycloaddition of propargylic esters with o-hydroxyphenyl substituted secondary phosphine oxides (SPOs) was established, which afforded a series of phosphorus-containing six-membered heterocycles in high yields (up to 99 % yield). This reaction represents the first α,β-regioselective (2+n) cycloaddition of propargylic esters via the intermediates of copper−allenylidenes, which will enrich the chemistry of propargylic esters and copper−allenylidenes. Moreover, this work also represents the first application of o-hydroxyphenyl substituted SPOs as 1,4-dinucleophiles in (2+4) cycloadditions, which provides a useful protocol for the synthesis of phosphorus-containing six-membered heterocycles with potential bioactivity.

An efficient and simple one-pot synthesis of structurally diverse novel tetrahydroquinolin fused iminosugars was developed through the aza-Diels-Alder mechanism. The adaptability of this method has been demonstrated by a variety of imines and D/L-ribose tosylates, and both electron-donating and withdrawing substituted imines are employed in reaction well. In addition, this reaction is characterized by simple operation, good yield, and high atom economy. Some synthetic iminosugars showed moderate anti proliferation of HCT116 tumor cells.

An acid catalyzed one-pot condensation of readily available cyclic β-diketones, arylglyoxals and arylhydrazones produces a library of diversely functionalized pyrazole derivatives in excellent yield under metal-catalyst-free benign conditions.

Abstract

A one-pot, three-component, and atom economic synthesis of biologically and pharmaceutically important fully substituted and functionalized pyrazole derivatives has been accomplished under metal-catalyst-free benign conditions. The strategy involves early condensation of readily available cyclic β-diketones (dimidone, 4-hydroxycoumarin and 2-hydroxy-1,4-naphthoquinone) and arylglyoxals to generate a chalcone type intermediate which upon acid catalyzed condensation with ambident nucleophile arylhydrazones produces various aryl and cyclic β-diketone substituted pyrazole derivatives. The synthesis embraces high functional group tolerance, broad substrate scope, excellent yield of the products, short reaction time and operationally simple and mild reaction conditions. The synthesis provides an easy opportunity of incorporating biologically important N-diarylsulfide/selenide functionality, various enolisable cyclic β-diketones and other bioactive heterocycles concurrently to pyrazole, which may help in designing and development of pyrazole derivatives of pharmacological significance.