Empowering Visible Light Catalysis: Brominative Dearomatizationof Biaryl Ynones

Abstract

A step-economic photo-oxidative brominative carbannulation of biaryl ynones employing bromide source and riboflavin tetraacetate (RFTA) have been developed. The switchable reactivity between distal phenyl C-H activatedortho-annulation and dearomative ipso-annulation are well exemplified.The eminent features of the methodology include metal-free, externaladditive free, low-cost photocatalyst, use of simple precursor. Further, we elaborately discussed about the mechanistic investigation and the applicabilityof additional functional group incorporation.

Photo-redox Catalyzed C-S and C-C Bond Forming Cascade Cy-clization/Dearomatization of Biaryls: Sustainable Route to Func-tionalized Spirocyclohexa[5.5] and [4.5]trienones

“…Inspired by our previous work on photo-induced brominative carbannulation of biaryl ynones, 15 initially, we wished to access trifluoromethylthiolated spiro [5.5]trienones from 1-(4'-methoxy-[1,1'-biphenyl]-2-yl)-3-phenylprop-2-yn-1-one (1a) and commercially available and bench-stable Silver(I)trifluoromethanethiolate (AgSCF3) (4A) via dearomative ipso-annulation. To this end, we started our investigation by taking the mixture of compounds 1a (0.1 mmol) and 4A (0.11 mmol) in dry acetonitrile (3 mL) under irradiation of single 0.9W blue LED light (455 nm) with N2 protection at room temperature and the reaction could furnish the dearomative ipso-annulated product 2'-phenyl-3'-((trifluoromethyl)thio) -4'H-spiro[cyclohexa[2,5] diene-1,1'-naphthalene]-4,4'-dione (5a) in 68% isolated yield (Table 1, entry 13).…”

“…Therefore, the development of more efficient and green process for trifluoromethylthiolation and sulfonylation reactions of C-C unsaturated bond via radical cascade cyclisation is still in demand. With our continued interest in dearomative spirocyclisations 14 and photochemical reactions 15 we explored the present visiblelight mediated approach for the generation of spiro [4.5] and [5.5]trienones featuring -SCF3, -SO2Ar, -SAr, -COAr. This methodology represents significant advances in photochemical C-S and C-C bond formation of biaryl ynones that overcomes existing challenge associated with the uncontrolled photodecomposition processes occurring due to the high-energy photons.…”

Photoredox‐Catalyzed Thiocyanative Cyclization of Biaryl Ynones to Thiocyanated Spiro[5.5]trienones: An External‐Oxidant‐ and Transition‐Metal‐Free Approach

“…Consequently, metal-free and inexpensive photocatalytic procedures are highly desirable. Recently, metal-free photocatalyst including RFTA, [27] Eosin Y, [28] (MesÀ AcrÀ MeBF 4 ), [24a,29] and 4CzIPN [30] were revealed as an efficient photocatalyst for dearomatization reactions. For a long time, our group has been working on dearomatization of arenes [27,31] under mild and sustainable conditions.…”

“…Recently, metal-free photocatalyst including RFTA, [27] Eosin Y, [28] (MesÀ AcrÀ MeBF 4 ), [24a,29] and 4CzIPN [30] were revealed as an efficient photocatalyst for dearomatization reactions. For a long time, our group has been working on dearomatization of arenes [27,31] under mild and sustainable conditions. Herein, we would like to disclose the dearomatization of biaryl ynones via cascade CÀ C and CÀ S bond formation in a single pot led to the formation of SCN-modified spiro [5.5]trienones (Scheme 1c), under visible light-mediated organophotoredox catalyzed external oxidant free condition.…”

Visible Light Promoted Brominative Dearomatization of Biaryl Ynones to Spirocycles

“…The other examples for the synthesis of spiro[5.5]-compounds as well as dibenzocycloheptene-5-ones mainly include transition-metal-mediated/catalyzed and radical induced , conditions. During preparation of our manuscript (pre-communication, 10.26434/chemrxiv-2022-dccgz), the Yang group developed dearomatization of biaryl ynones to construct polychloromethylated and halogenated spiro[5.5]­trienones at elevated temperature in which polyhaloalkanes were used as the precursor . Despite the increasing urge to implement energy-efficient and green reactions even on the laboratory scale through visible light as an ideal reagent, the light promoted pathway have been less explored .…”