Iron‐Catalyzed Silylation and Spirocyclization of Biaryl‐Ynones: A Radical Cascade Process toward Silylated Spiro[5.5]trienones

Abstract

Iron‐catalyzed cascade silyl radical addition/6‐exo‐trig cyclization/dearomatization of biaryl ynones has been developed. This approach uses silane as the precursor of silyl radical as well as silylation reagent, 1,10‐phenanthroline as the ligand, and tert‐butyl hydroperoxide (TBHP) as the oxidant. By employing this tandem process, a series of silylated spiro[5.5]trienones were prepared.

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

“…Having said that, we further investigated the impact of other organic photocatalysts like Eosin Y, Eosin B, RFTA, and Rose Bengal, on this transformation, and we ended up with a poor yield of 2 a (entries 12-15). The findings of the screening of various oxidants, including K 2 S 2 O 8 , TBHP, and BPO in addition to molecular oxygen (entries [16][17][18], revealed that molecular…”

“…Following that, the reactions of 1 a and 1 a' with NH 4 SCN (2 a) were carried out under the ideal reaction conditions with H 2 18 O instead of H 2 O. 18 O-labelled spiro [5.5]trienone 2 a was detected in both cases by HRMS (see the supporting information).…”

“…After the development of the first‐ever spiro[5.5]trienones or dibenzocycloheptene‐5‐ones by Chen and co‐workers through the intramolecular electrophilic cyclization of biaryl ynones [16] . The groups of Xia, [17] Chen, [18] Wang, [19] Zhang, [14a] and Duan [13e] independently reported the transition ‐metal catalyzed dearomatizations of biaryl ynones to spiro[5.5]trienones. Although each of these approaches efficiently yields spiro[5.5]trienones with various substituents, doing so entails the use of costly metal catalysts and/or exterior oxidants, which in turn confine the compatibility of the functional groups and result in the production of toxic byproducts.…”

Electrochemical Arene Radical Cation Promoted Spirocyclization of Biaryl Ynones: Access to Alkoxylated Spiro[5,5]trienones

“…Radical-mediated dearomative spirocyclization reaction of biaryl ynones is one of the most straightforward and appealing approaches to access value-added spiro­[5,5]­trienones. − Over the past few decades, increasing efforts have been devoted to the development of structurally diverse radical precursors, such as C-centered, N-centered, P-centered, S-centered, Se-centered, and Si-centered radical precursors, to react with biaryl ynones for achieving the radical-mediated dearomative spirocyclization reaction (Scheme a). Among these established synthetic approaches, radical species are usually preferentially generated via chemical, photochemical or electrochemical processes and add to the CC bond moiety of biaryl ynones to achieve the dearomative spirocyclization reaction. − For instance, in 2021, Ackermann and co-workers described a novel electrochemically driven radical-mediated dearomative spirocyclization of biaryl ynones with CF 2 XSO 2 Na to furnish diverse tri- and difluoromethylated spiro­[5,5]­trienones in an undivided cell .…”

“…Radical-mediated dearomative spirocyclization reaction of biaryl ynones is one of the most straightforward and appealing approaches to access value-added spiro­[5,5]­trienones. − Over the past few decades, increasing efforts have been devoted to the development of structurally diverse radical precursors, such as C-centered, N-centered, P-centered, S-centered, Se-centered, and Si-centered radical precursors, to react with biaryl ynones for achieving the radical-mediated dearomative spirocyclization reaction (Scheme a). Among these established synthetic approaches, radical species are usually preferentially generated via chemical, photochemical or electrochemical processes and add to the CC bond moiety of biaryl ynones to achieve the dearomative spirocyclization reaction. − For instance, in 2021, Ackermann and co-workers described a novel electrochemically driven radical-mediated dearomative spirocyclization of biaryl ynones with CF 2 XSO 2 Na to furnish diverse tri- and difluoromethylated spiro­[5,5]­trienones in an undivided cell . Although considerable methods exist for preparing spiro­[5,5]­trienones through a radical dearomatization strategy, the challenge with these accomplishments, however, is that they usually require the participation of additional radical precursors to trigger the dearomatization process.…”