Non‐classical S‐Heteroacenes with o‐Quinoidal Conjugation and Open‐Shell Diradical Character

Abstract

A series of non-classical S-heteroacenes were synthesized and exhibited intriguing physical properties and chemical reactivities that are very different from classical acenes. X-ray crystallographic analyses revealed that all acenothiophene derivatives Ph-AT-1-Ph-AT-3 had an o-quinoidal π-conjugation with large bond-length alternation, whereas the acenodithiophene derivative Ph-ADT-3 easily dimerized or reacted with oxygen to form a peroxy-bridged dimer. The long acenothiophene Ph-AT-4 was also highly reactive. The origin of these unique properties was investigated carefully by both experiments and theoretical calculations. The high reactivity of the long non-classical S-heteroacenes can be explained by their intrinsic open-shell diradical character as well as the o-quinoidal conjugation.

Strain‐Promoted 1,3‐Dithiolium‐4‐olates–Alkyne Cycloaddition

“…In presence of 2,3‐naphthyne precursor, the desired S‐heteroacenes 38 and 39 were isolated in 55 and 59 % yield, respectively. Interestingly, the acenothiophenes 29 and 38 were recently reported by the group of Chi, by means of a Paal–Knorr sequence in 65 and 50 % yield, respectively, from the corresponding diketones . These results show the divergence of SPDAC over current available methods.…”

Synthesis, Aromaticity, and Application of peri‐Pentacenopentacene: Localized Representation of Benzenoid Aromatic Compounds

“…Knowing that the ortho ‐quinoid molecules like benzo[ c ]thiophene and indeno[2,1‐ a ]fluorene have much higher stability than that of their longer homologues, namely, the naphtho[2,3‐ c ]thiophene and benzo[ c ]indeno[2,1‐ a ]fluorene, respectively, therefore, the localized representation (LR) should have the biggest weight among all the resonance structures since it generates ortho ‐fused dienes units of the lowest dimensionality (Figure 2). [38, 39] Also, on top of the middle ring, the two neighbouring rings could formally be written with 6 π‐electrons in the two corresponding Kekulé structures. Indeed, with this representation, 3 rings out of 5 can be written with 6 π‐electrons even though the only proper aromatic sextet like benzene is the central one (rings in blue, Figure 1).…”

Strain‐Promoted 1,3‐Dithiolium‐4‐olates–Alkyne Cycloaddition

“…[31] In presence of 2,3-naphthyne precursor,t he desired S-heteroacenes 38 and 39 were isolated in 55 and 59 %y ield, respectively.I nterestingly,t he acenothiophenes 29 and 38 were recently reported by the group of Chi, by means of aP aal-Knorr sequence in 65 and 50 %yield, respectively,from the corresponding diketones. [32] These results show the divergence of SPDAC over current available methods.T he reaction with ortho-fused 1,2-naphthyne and 3,4-phenanthryne precursors delivered the helical derivatives 40 and 41,respectively,ingood yields.Finally,the thiophenes 42-44 were isolated in 47 to 63 %yield. Theuse of 9,10-phenanthryne is particularly interesting because it generates phenanthro [9,10-c]thiophenes such as 43,w hose synthesis has so far only been preliminarily explored.…”

“…Interestingly, acenothiophenes 29 and 38 were recently reported by the group of Chi, by means of a Paal-Knorr sequence in 65% and 50% yield ?, respectively, from the corresponding diketones. 31 These results show the divergence of SPDAC over current available methods. The reaction with ortho-fused 1,2naphthyne and 3,4-phenanthryne precursors delivered the helical derivatives 40 and 41 in good yield.…”