Chemodivergent Chalcogenation of Aryl Alkynoates or N-Arylpropynamides Using 9-Mesityl-10-Methylacridinium Perchlorate Photocatalyst.

Herein we report a cascaded chalcogenation of aryl alkynoates or N-arylpropynamides using 9-mesityl-10-methylacridinium perchlorate as a visible light photocatalyst to obtain selectively either 3-sulfenylated/selenylated coumarins or spiro[4,5]trienones. In a radical initiated process, the spiro-cyclization reaction was favored due to the presence of a -OMe or -F substituent at the para position of the aryl group, which helped to stabilize the allylic radical intermediate formed during the reaction. Otherwise, 6-endo-trig cyclization led to 3-sulfenylated/selenylated coumarins. Overall, the new C-S/C-Se, C-C, and C═O bonds were formed in a single step. The Stern-Volmer quenching study, EPR experiments, light ON-OFF experiments, radical trapping experiments, etc., helped to understand the radical-based mechanism.

CsPbBr3 Perovskite Photocatalyst in Chemodivergent Functionalization of N-Methylalkanamides Using CBr4.

Herein we have developed a strategy for chemodivergent functionalization of N-methylalkanamides via C-Br bond activation of CBr4, using an orthorhombic CsPbBr3 perovskite photocatalyst under blue LEDs (450-470 nm). The selectivity of whether a 5-exo-trig spiro cyclization or a 6-endo-trig cyclization occurred depended on the stability of the radical intermediate that was formed after the addition of the bromide radical to the starting compound to obtain 3,8-dibromo-1-methyl-4-phenyl-1-azaspiro[4.5]deca-3,6,9-trien-2-on or 3-bromo-1-methyl-4-phenyl-1-azaspiro[4.5]deca-3,6,9-triene-2,8-dione or 3-bromo-6-(tert-butyl)-1-methyl-4-phenylquinolin-2(1H)-one.

3-Arylsulfonylquinolines from N-Propargylamines via Cascaded Oxidative Sulfonylation Using DABSO.

We report a cascaded oxidative sulfonylation of N-propargylamine via a three-component coupling reaction using DABCO·(SO2)2 (DABSO). 3-Arylsulfonylquinolines were obtained by mixing diazonium tetrafluoroborate, N-propargylamine, and DABSO under argon atmosphere in dichloroethane (DCE) for 1 h. In a radical pathway, DABSO was utilized as the sulfone source and an oxidant in this radical-mediated cascaded reaction.

t BuOLi-promoted terminal alkyne functionalizations by aliphatic thiols and alcohols.

Selective radical addition to terminal alkynes is always a difficult task to achieve because it gives a mixture of stereo- and regioisomers. Herein we describe the selective addition of aliphatic thiols or alcohols to N-phenylpropiolamides (terminal alkynes) using lithium tert-butoxide (tBuOLi) in ethanol as a promoter. Mechanistically, it has been shown that the reaction proceeded through the generation of a thiyl radical intermediate, and the amide group in N-phenylpropiolamide could help in the activation of the alkyne, which led to thioacetalization via the formation of a (Z)-selective anti-Markovnikov vinyl sulfide. The (Z)-selectivity during the formation of vinyl sulfides was controlled by an intramolecular sulfur⋯oxygen interaction.

Chlorinative Cyclization of Aryl Alkynoates Using NCS and 9-Mesityl-10-methylacridinium Perchlorate Photocatalyst.

In a chlorinative cyclization, Mes-Acr-MeClO4 acted as a visible-light photocatalyst to obtain 3-chlorocoumarins from aryl alkynoates and N-chlorosuccinimide (NCS). The radical initiated reaction proceeded in a cascading manner via Cl- addition to alkynoates. Next, 5-exo-trig spirocyclization and subsequent 1,2-ester migration led to the formation of C-C and C-Cl bonds.

Disulfide metathesis via sulfur⋯iodine interaction and photoswitchability.

The idea of constitutional dynamic chemistry (CDC) and dynamic combinatorial chemistry (DCC) is widespread in the literature using the chemistry of disulfides. The synthesis of unsymmetrical diaryl disulfides is challenging due to the presence of a weak S-S bond. We report herein the synthesis of unsymmetrical diaryl disulfides from two symmetrical disulfides via a cross-metathesis reaction which was controlled by a weak sulfur⋯iodine (S⋯I) interaction. The unsymmetrical disulfides were stable in acetonitrile solution in the presence of N-iodosuccinimide (NIS), and found to be reversibly photoswitchable to the symmetrical disulfides under visible light irradiation.

Sulfuroxygen interaction-controlled (Z)-selective anti-Markovnikov vinyl sulfides.

The sulfur oxygen (SO) interaction was used herein to obtain (Z)-selective anti-Markovnikov vinyl sulfides from the addition of thiyl radicals to terminal alkynes. DFT calculations predicted that SO interaction originated from the delocalization of the lone-pair of the carbonyl oxygen to the adjacent σ* orbital of the S atom of C-S.

Dithioacetalization or thioetherification of benzyl alcohols using 9-mesityl-10-methylacridinium perchlorate photocatalyst.

We report herein the use of 9-mesityl-10-methylacridinium perchlorate as the visible-light photocatalyst for dithioacetalization or thioetherification of benzyl alcohols in one pot using aerial dioxygen as a terminal oxidant. EPR analysis and Stern-Volmer quenching studies helped to rationalize the single electron transfer (SET) mechanism.