Abstract:In general, aromatic cores are stable owing to their resonance energies. Different from facile peripheral modifications of aromatic cores, transforming an aromatic core into a different skeleton is ambitious and has attracted only little attention as a general synthetic method. This personal account shows our journey to inventing transformations of dibenzothiophenes into triphenylenes, carbazoles, and spirocyclic diarylfluorenes and to establishing 'aromatic metamorphosis' as a useful and game-changing strateg… Show more
“…Once dithia [8]helicene is synthesized, we would be able to take advantage of our synthetic strategy about endocyclic transformations of thiophene compounds, which we have coined 'aromatic metamorphosis'. 13 According to our previous reports about the transformations of dibenzothiophene S,S-dioxides into carbazoles 14 and uorenes, 15 we expected the synthesis of diaza [8]helicene and the carbon analog from the sulfone being feasible, although one concern would lie in the chirality conversion during the aromatic metamorphosis. Here we report that the asymmetric synthesis of a series of dihetero [8]helicenes has been indeed viable.…”
A series of dihetero[8]helicene have been systematically synthesized in enantiomerically enriched forms by utilizing the characteristic transformations of organosulfur functionality. The synthetic route begins with assembling a ternaphthyl common synthetic...
“…Once dithia [8]helicene is synthesized, we would be able to take advantage of our synthetic strategy about endocyclic transformations of thiophene compounds, which we have coined 'aromatic metamorphosis'. 13 According to our previous reports about the transformations of dibenzothiophene S,S-dioxides into carbazoles 14 and uorenes, 15 we expected the synthesis of diaza [8]helicene and the carbon analog from the sulfone being feasible, although one concern would lie in the chirality conversion during the aromatic metamorphosis. Here we report that the asymmetric synthesis of a series of dihetero [8]helicenes has been indeed viable.…”
A series of dihetero[8]helicene have been systematically synthesized in enantiomerically enriched forms by utilizing the characteristic transformations of organosulfur functionality. The synthetic route begins with assembling a ternaphthyl common synthetic...
“…Recently, it has been reported that dibenzothiophenes can be converted into a variety of ring systems, such as dibenzosiloles, dibenzophospholes, fluorenes, and carbazoles [ 22 , 23 , 24 , 25 , 26 ]. Transformation to dibenzosiloles and dibenzophospholes involves (1) the generation of 1,1′-dianions via desulfurative dilithiation with lithium metal and (2) the subsequent reaction of the resulting 1,1′-dianions with silicon and phosphorus electrophiles, respectively.…”
[n]Helicenes with helically twisted structures have attracted increasing interest owing to their unique properties. Therefore, it has been an important issue to develop facile synthetic methodologies which allow access to a variety of [n]helicenes. Here we report the synthesis of [7]helicenes and [7]helicene-like compounds from the thia[7]helicene as a common starting material. Desulfurative dilithiation of the thia[7]helicene and the subsequent reaction with silicon and phosphorus electrophiles afforded the silole- and phosphole-fused [7]helicene-like compounds, respectively. The cyclopentadiene-fused [7]helicene-like compound and the pyrrole-fused aza[7]helicenes were also successfully synthesized via twofold SNAr reactions of the thia[7]helicene S,S-dioxide with the carbon and nitrogen nucleophiles, respectively. The thia[7]helicene S,S-dioxide showed a slightly red-shifted absorption spectrum than the parent thia[7]helicene, which was well demonstrated by the theoretical calculations. The substituents on the silicon atom of silole-fused [7]helicene-like compounds have little impact on the longest absorption maximum. Such little effect of the substituents on absorption properties was also observed for cyclopentadiene-fused [7]helicene-like compounds and aza[7]helicenes and was well demonstrated by the theoretical calculations. The thia[7]helicene S,S-dioxide and the silole-fused [7]helicene-like compound exhibited bright blue emission, and the cyclopentadiene-fused [7]helicene-like compound and the aza[7]helicenes showed strong violet emission. Each single enantiomer of the aza[7]helicenes showed circularly-polarized luminescence with the dissymmetry factors of 4.2⁓4.4 × 10−3.
“… [a] The conversions of 1a were usually >95 % unless otherwise noted. The second intramolecular S N Ar reaction would be the rate‐limiting step, and, according to our previous reports, [17–25] the major by‐product would be the corresponding zwitterionic species shown below, which was difficult to quantify.…”
Dedicated to Dr. E. Peter Kündig on the occasion of his 75th birthdayTreatment of a mixture of dibenzothiophene dioxides and benzaldehyde N-benzylimines with potassium hexamethyldisilazide induces sequential intermolecular and intramolecular S N Ar reactions to eventually form the corresponding 5H-dibenzo[c,e]azepines without any formation of the conceivable five-membered fluorene derivatives.
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