Visible Light-Promoted Regioselective Benzannulation of Vinyl Sulfoxonium Ylides with Ynoates

Abstract

Herein, we report a highly regioselective [4 + 2]-annulation of vinyl sulfoxonium ylides with ynoates under light-mediated conditions. The reaction proceeds through the new dienyl sulfoxonium ylide, which undergoes photolysis under blue light irradiation to give highly substituted naphthalene scaffolds. The method presented here operates at room temperature and does not require the addition of an external photosensitizer. The in situ-generated dienyl sulfoxonium ylide absorbs light and acts as a photosensitizer for the formation of arenes. The synthetic potential of these benzannulations was further illustrated by various synthetic transformations and a scale-up reaction. Moreover, control experiments and quantum chemical calculations reveal the mechanistic details of the developed reaction.

Light-induced β-hydroxy sulfone synthesis in DNA-encoded libraries

“…Our study was initiated by a careful screening of reaction conditions (Scheme 1), using 4-vinylbenzamide ( 1o ) and sodium 4-chlorobenzenesulfinate ( 2 ) as model substrates, eosin Y as a photocatalyst, and nitrobenzene as a radical quencher, 27 in DMF/water under the irradiation of 3 W green light-emitting diodes (LEDs, λ max = 535 nm, I max = 1000 mA, 3.0 W; in addition to Eosin-Y, other organophotocatalysts were evaluated too, and the findings indicated that Eosin-Y was the most effective – see ESI,† general information, pages S5 and S159, for further details). We started by analysing the influence of medium acidity (entries 1–4) and rapidly observed that at a 1 : 2 ratio of eosin Y (EY) to HCl, in which EY was present in the reaction in the neutral form, the conversion was enhanced.…”

“…In the absence of Eosin Y, the reaction proceeded with a 21% conversion rate, which was likely the result of oxygen-driven photochemistry (entry 21). 27 Despite being conducted in complete darkness, the reaction could still occur. It was postulated to have commenced shortly after the reaction was established before being placed in a dark compartment (entry 22).…”

“…In the absence of nitrobenzene, which is essential for the reaction to proceed, oxygen could serve as a radical quencher (entry 23). 27 In contrast to the optimal conditions, the conversion rate is significantly reduced when exposed to air, due to solvent evaporation (entry 24).…”