Facile synthesis and functionalization of fluoranthenes via intramolecular[4+2]annulations between thiophenes and alkynes

Fluoranthenes have attracted tremendous attention due to their unique optoelectronic properties and extensive applications.Although several synthetic methodologies have been developed for the preparation of fluoranthene derivatives,it is still unfavorable to functionalize the fluoranthene framework at different positions due to the relatively low selectivity and reactivity.Herein,a catalyst-free intramolecular[4+2]annulation between thiophenes and alkynes is developed towards the synthesis of fluoranthenes.Altogether 20 examples have been demonstrated using this method.Various functional groups can be precisely introduced into the fluoranthene skeleton at different positions by simply tuning the substituents on the thiophenes and alkynes.The conjugation of the fluoranthene can be facilely extended through different directions.Furthermore,the feasibility of this[4+2]annulation reaction is also investigated by density functional theory calculations.Therefore,this protocol provides not only a synthetic methodology towards fluoranthenes with substituents functionalized at different positions,but also an effective pathway to construct large polycyclic aromatic hydrocarbons containing fluoranthene moieties.

Facile Synthesis of S-Fused Multi-Membered Polycyclic Heterocycles:A Construction Strategy towards Thermally Stable Thiepine Derivatives

S-fused heterocycles have become popular building blocks to construct functional polycyclic compounds.In contrast to the abundant synthetic methodologies for thiophene-fused aromatics,the synthesis of S-heterocycles containing six-membered thiopyran and seven-membered thiepine rings is much less reported owing to their unfavorable synthetic protocols and the thermal instabilities.Herein,a series of thiepine-containing polycyclic S-heterocycles have been successfully synthesized via different synthetic routes which involve initial construction of sulfur bridges and final ring-closure reactions.Therefore,the dilithium intermediates are ex-cluded,which facilitates the fusion on the thiepine ring with different S-heterocycles,including thiophene and thiopyran derivatives.Typically,a S-fused multi-membered polycyclic compound simultaneously involving thiophen,thiopyran,and thiepine rings has been successfully prepared.Interestingly,nucleus-independent chemical shift calculations reveal that the incorporated thiopyran and thiepine rings demonstrate aromatic and nonaromatic characteristics,respectively.Moreover,the thermal stabilities of the thiepine derivatives have been tremendously improved after the fusion on the three vinyl groups in the thiepine unit,which is attributed to the enhancements of the activation energies for the S-extrusion reactions,as revealed by density functional theory calculations.Therefore,our findings not only provide a facile synthetic methodology for S-fused multi-membered polycyclic heterocycles,but also furnish a novel construction strategy towards thermally stable thiepine derivatives.