Synthesis of Spirocyclic Diarylfluorenes by One-Pot Twofold S_NAr Reactions of Diaryl Sulfones with Diarylmethanes

Abstract

Treatment of dibenzothiophene dioxides with cyclic diarylmethanes in the presence of KN(SiMe3)2 results in the formation of fluorene-based spirocyclic tetraarylmethanes in a single operation. The transformation would proceed via an intermolecular SNAr reaction of the dioxides with cyclic diarylmethylpotassium followed by intramolecular SNAr cyclization. This straightforward strategy provides a wide range of spirocyclic diarylfluorenes including unusual ones that are otherwise difficult to synthesize.

One‐Pot Synthesis of Spiro[fluorene‐9,9'‐xanthene] Derivatives

“…Yorimitsu reported the synthesis of spiro rings via a nucleophilic aromatic substitution reaction in 2016. [ 28 ] Various fluorenyl synthetic aromatic hydrocarbons were obtained in middle‐high yields from dibenzo[ b,d ]thiophene 5,5‐dioxide and xanthene using KN(SiMe 3 ) 2 as catalyst and heating at 80 o C for 16 h. Compared to the multi‐step and one‐pot methods, the nucleophilic aromatic substitution is a new synthetic strategy to synthesize spiro compound. Different from the traditional Friedel‐Crafts reaction, the mechanism of this experiment is based on a nucleophilic aromatic substitution reaction, S N Ar.…”

“…[ 6,9,19‐22 ] Moreover, from the perspective of synthesis method, as spirofluorenes, both SBF and SFXs can be synthesized using a multi‐step synthesis pathway (Grignard reagent; n ‐butyl lithium; or prepared with p ‐trimethylsilylphenylboronic acid, including the diarylfluorene, dibiarylketone and the reaction of xanthone and o‐ halobiaryl. [ 13,21,23‐26 ] But it is difficult to achieve highly efficient and convenient mass synthesis. Compared to SBF, the synthesis method of SFXs is more diverse due to the difference in the xanthene part.…”

Deep‐blue light‐emitting polyfluorenes containing spiro[fluorene‐9,9′‐thioxanthene‐S,S‐dioxide] isomers

“…Spiro[Fluorene-9,9 0 -Thioxanthene](1) 31,32 Under nitrogen atmosphere, 2-bromobiphenyl (1.17 g, 5 mmol), magnesium granules (1.22 g, 50 mmol), and a grain of iodine in dry THF (2 mL) were heated to reflux to induce Grignard reaction. Then the remaining 2-bromobiphenyl (8.16 g, 35 mmol) in dry THF (40 mL) were added slowly into the reaction, [1,1 0 -biphenyl]-2-ylmagnesium bromide was obtained after the mixture was heated to reflux for 4 h. Thiaxanthone (2.12 g, 10mmol) was added into the prepared Grignard reagent and the mixture was kept under reflux for overnight.…”

“…White solid (2.73 g, yield 78.3%) was obtained by column chromatography with petroleum ether as eluant. Spiro[Fluorene-9,9 0 -Thioxanthene-S,S-Dioxide](2) 31 Spiro[fluorene-9,9 0 -thioxanthene] (1.74 g, 5mmol) and H 2 O 2 (4 mL, 40mmol) in AcOH/THF (40 mL, v:v 5 1:1) were stirred at 100 8C for 8 h. White solid (1.68 g, yield 88.4%) was obtained after the reaction mixture was cool and filtered. 1 26 Spiro[fluorene-9,9 0 -thioxanthene-S,S-dioxide] (1.52 g, 4mmol) was dissolved in CHCl 3 /CF 3 COOH (30 mL, v:v 5 1:1), and NBS (1.46 g, 8.3mmol) was added in portions.…”

Aromatic Metamorphosis of Dibenzothiophenes

“…After screening many nucleophiles, including a malonate ester, we found cyclic diarylmethanes such as xanthene to be suitably reactive under similar conditions to those shown in Scheme 7 (Scheme 11). 29 The products were spirocyclic 9,9-diarylfluorenes, which have been attracting increasing attention in organic electronics. 30 In contrast to the conventional Friedel-Crafts-based synthetic strategies, 31 our protocol employs basic conditions.…”