Asymmetric Dearomatization of Electron-Deficient Heteroarenes by a Phosphine-Catalyzed[3+2]Annulation with Vinylcyclopropanes

Asymmetric dearomatization reactions of various electron-deficient heteroarenes,including benzofurans,benzothiophenes,and indoles,have been described.Through a phosphine-catalyzed[3+2]annulation with vinylcyclopropanes,readily available heteroarene feedstocks undergo smooth dearomatization reactions,delivering a diverse array of valuable chiral cyclopentabenzodihydrofuran and cyclopentaindoline scaffolds in a highly diastero-and enantioselective manner.Notably,the employment of cyclopropanes in phosphine-mediated annulation for the dearomatization of electron-deficient arenes is unknown.

Copper-catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylides withβ-trifluoromethyl-substituted alkenyl heteroarenes

Copper-catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylides andβ-trifluoromethyl-substituted alkenyl heteroarenes was developed for the first time.A wide range of enantioenriched pyrrolidines containing both heteroarenes and trifluoromethyl group with multiple stereogenic centers could be readily accessible by this method with good to high yields and excellent levels of both stereo-and regioselectivity(up to 99%yield,>20:1 rr,>20:1 dr,and up to 95%ee).Notably,substratecontrolled umpolung-type dipolar cycloaddition was also disclosed in this protocol to achieve regiodivergent synthesis withα-aryl substituted aldimine esters as the dipole precursors.Systematic DFT studies were conducted to explore the origin of the stereo-and regioselectivity of this 1,3-dipolar cycloaddition,and suggest that copper(Ⅱ)salt utilized in this catalytic system could be reduced in-situ to the active copper(Ⅰ)species and might be responsible for the observed high stereo-and regioselectivity.

Direct Introduction of EthoxycarbonyldifluoromethyI-Group to Heteroarenes with Ethyl Bromodifluoroacetate via Visible-Light Photocatalysis

A mild and versatile approach for the direct introduction of ethoxycarbonyldifluoromethyl-group to heteroarenes via visible-light photocatalysis has been developed. The new photoredox protocol has enabled the difluoromethylenation of heteroarenes containing a wide range of common functional groups under mild conditions.

Sigmatropic rearrangements of B(MIDA)-propargylic alcohols towards the diverse synthesis of α-functionalized organoborons

α-Functionalized organoborons are useful building blocks and key structural elements in functional molecules.Their previous synthesis relied on the famous Matteson reaction or the late-stage borylative modification of alkynes or alkenes.Recently,the synthetic transformation of borylated building blocks offers another useful strategy and is currently actively explored.We report herein that B(MIDA)-propargylic alcohols(BPAs) are a useful type of borylated building blocks.Bearing two complementary functional group handles(alkyne and hydroxyl) in close proximity,the redox-neutral [3,3] and [2,3] sigmatropic rearrangements of BPAs allow the efficient synthesis of several types of α-functionalized boronates,including α,β-unsaturated acylborons,α-S/P-substituted allenylborons,boryl-substituted thiazoles and a borylated α,β-unsaturated hydrazine,some of which are otherwise challenging targets using other synthetic methods.

Fabrication of Graphitic Carbon Nitride-Based Film:An Emerged Highly Efficient Catalyst for Direct C-H Arylation under Solar Light

Main observation and conclusion Photoredox C-H bond formation can proceed in aerobic environment under solar light and has therefore become attractive.Nowa-days,different types of expensive novel metal complexes and nanomaterials have been urbanized as photocatalysts for direct C-H bond formation in between derivatives of heteroarenes(HAs)and aryl diazonium salts.These photocatalysts,however,still suffer from poor stability,high cost,and decay.Herein,a graphitic carbon nitride-based fluorescein isothiocyanate(g-C_(3)N_(4)-FITC)film pho-tocatalyst has been reported,which shows ecellent light harvesting ability,and band gap suitability to catalyze the metal free direct C-H arylation of HAs under solar light at ambient temperature.Moreover,the g-C_(3)N_(4)-FITC film photocatalyst can be reused four times without significant loss of activity,confirming the excellent photocatalytic stability.The current strategy to constructa g-C_(3)N_(4)-FITC film photocatalyst for direct C-H arylation opens a new path towards replacing metal-based catalysts in fine chemical Sy nthesis.