Catalytic Radical-Triggered Annulation/Iododifluoromethylation of Enynones for the Stereospecific Synthesis of 1-Indenones

Construction of C-S and C-Se Bonds via Photocatalytic Aromatization-Driven Deconstructive Diversification of Spiro-Dihydroquinazolinones Derived from Unstrained Ketones

A novel and robust deconstructive functionalization reaction of spiro-dihydroquinazolinones with sulfenylating reagents in the presence of base has been realized under visible light irradiation. This reaction enabled the direct ring-opening of unstrained cyclic ring systems, producing skeletally diverse functionalized quinazolinones with moderate to good yields. A range variety of sulfenylating reagents including diaryl disulfide, thiosulfonate, dithiosulfonate and 1-[(trifluoromethyl)thio]-2,5-pyrrolidinedione were compatible for this transformation. In addition, diaryl diselenide and selenosulfonate could also couple with spiro-dihydroquinazolinones to form C-Se Bonds. Mechanistic studies revealed that the reaction proceeds via a radical-radical coupling pathway.

Metal-free radical cascade cyclization/haloazidation of enynones to access functionalized 1-indanones

A novel three-component radical cyclization/haloazidation of enynones, employing TMSN3 as the azide source and NIS (NBS or NCS) as the halogen source, has been developed under metal-free conditions for the efficient synthesis of various 1-indanones with moderate yields and acceptable Z/E ratio. The reaction progresses through a sequence involving radical addition, 5-exo-dig cyclization, and radical coupling, ultimately resulting in the formation of three new chemical bonds and a new ring in a single step. The synthetic benefits of this method have been proven by large-scale experiments and late-stage modification.

Photoredox-Catalyzed Alkynylation of C(sp3)-H Bonds Adjacent to a Nitrogen Atom of Tertiary Amines with Alkynyl Bromides

A novel and robust alkynylation of C(sp3)-H bonds adjacent to a nitrogen atom of tertiary amines with alkynyl bromides as radical alkynylating reagents has been realized under visible-light irradiation. A range variety of tertiary amines including N-arylamines and N-alkylamine have been coupled with both aromatic and aliphatic alkynyl bromides to furnish 51 examples of propargylamines in moderate to excellent yields (31-80% yields). The possible mechanism was a radical addition-elimination process based on preliminary mechanistic studies.

Assembly of functionalized gem-difluoroalkenes via photocatalytic defluorocyanoalkylation and defluoroacylation of α-CF3 styrenes with oxime esters

We report an efficient photocatalytic protocol for the defluorocyanoalkylation and defluoroacylation of α-trifluoromethyl styrenes by utilizing oxime esters as radical donors, allowing for the preparation of diverse gem-difluoroalkenes. The treatment of α-trifluoromethyl styrenes with cyclobutanone oxime esters led to the formation of distal cyano group-anchored gem-difluoroalkenes. Notably, adding K2CO3 as an inorganic base to the photocatalytic system afforded γ,γ-difluoroallylic ketones by utilizing acyl oxime esters as the acylating agents. Preliminary mechanistic investigations into this reaction pathway revealed the involvement of single-electron reduction, C-C bond cleavage initiated by iminyl radicals, radical addition, and β-fluoride elimination steps.

Photocatalytic Thio/Selenosulfonylation-Bicyclization of Indole-Tethered 1,6-Enynes Leading to Substituted Benzo[c]pyrrolo[1,2,3-lm]carbazoles

The photocatalyzed radical-triggered thio/selenosulfonylation-bicyclization of indole-tethered 1,6-enynes has been established for the first time, enabling the synthesis of various previously unreported thio/selenosulfonylated benzo[c]pyrrolo[1,2,3-lm]carbazoles with moderate to good yields under mild conditions. The reaction pathway was proposed, consisting of energy transfer, homolytic cleavage, radical addition, 5-exo-dig, radical coupling, and a Mallory reaction cascade. This approach exhibits a wide substrate compatibility and excellent tolerability toward various functional groups and is characterized by its remarkable efficiency in both bond formation and annulation.

Photoinduced Alkylsulfonylation and Cyanoalkylsulfonylation of Morita-Baylis-Hillman Adducts via Multicomponent Insertion of Sulfur Dioxide

General and convenient visible-light-promoted alkylsulfonylation and cyanoalkylsulfonylation of MBH adducts have been developed through the multicomponent insertion of sulfur dioxide, enabling the assembly of two C-S bonds to generate structurally diverse allylic alkylsulfones (43 examples in total). The reaction of MBH adducts with potassium alkyltrifluoroborates and 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct afforded sulfones with generally good yields. Notably, the addition of N,N,N',N'-tetramethylethylenediamine as a base into the photocatalytic system led to yielding an alkyl sulfonyl unit and cyano group-anchored trisubstituted alkenes by utilizing cycloketone oxime esters as C-radical precursors. Both of these reactions have constructed two C-S bonds, and all desired products were obtained in moderate to excellent yields with complete stereospecificity.

Photoinduced radical tandem annulation of 1,7-diynes: an approach for divergent assembly of functionalized quinolin-2(1H)-ones

The first photocatalytic trichloromethyl radical-triggered annulative reactions of amide-linked 1,7-diynes with polyhalomethanes were established for the flexible assembly of functionalized quinolin-2(1H)-ones with generally acceptable yields. With the installation of the aryl group (R1) into the alkynyl moiety, C-center radical-initiated Kharasch-type addition/nucleophilic substitution/elimination cascade to produce quinolin-2(1H)-ones-incorporating gem-dihaloalkene, whereas three examples of polyhalogenated quinolin-2(1H)-ones were afforded when amide-linked 1,7-diynes bearing two terminal alkyne units were subjected to BrCX3 by exploiting dry acetonitrile as a solvent.

Phototriggered Fluoroalkylation/Cyclization of Unactivated 1-Acryloyl-2-cyanoindoles: Synthesis of RCOCF2-Substituted Pyrrolo[1,2-a]indolediones

A photochemical approach toward RCOCF2-substituted pyrrolo[1,2-a]indolediones was developed by the radical cascade difluoroalkylation/cyclization reaction of unactivated 1-acryloyl-2-cyanoindoles with ethyl iododifluoroacetate or iododifluoramides under visible-light irradiation. This transition-metal- and photosensitizer-free protocol afforded diverse difluoroalkylated pyrrolo[1,2-a]indolediones in moderate to good yields under mild reaction conditions. Most appealingly, the reaction can proceed smoothly under sunlight irradiation, which opens a new avenue toward difluoroalkylated pyrrolo[1,2-a]indolediones.

Photocatalytic Multicomponent Annulation of Amide-Anchored 1,7-Diynes Enabled by Deconstruction of Bromotrichloromethane

We present the first example of visible-light-mediated multicomponent annulation of 1,7-diynes by taking advantage of quadruple cleavage olf carbon-halogen bonds of BrCCl3 to generate a C1 synthon, which was adeptly applied to the preparation of skeletally diverse 3-benzoyl-quinolin-2(1H)-one acetates in moderate to good yields. Controlled experiments demonstrated that H2O acted as both oxygen and hydrogen sources, and gem-dichlorovinyl carbonyl compound exhibited as a critical intermediate in this process. The mechanistic pathway involves Kharasch-type addition/6-exo-dig cyclization/1,5-(SN")-substitution/elimination/binucleophilic 1,6-addition/proton transfer/tautomerization sequence.