Exploring the Photocyclization Pathways of Styrylthiophenes in the Synthesis of Thiahelicenes: When the Theory and Experiment Meet

Design and synthesis of thiahelicenes for molecular electronics

The conductance of a tunneling electron through a π-conjugated molecule may be affected by the presence of different pathways in the orbital structure of the molecule, resulting in the constructive or destructive interference of the molecular wave function. This quantum interference (QI) directly translates into enhancement or suppression of conductance and offers the possibility of controlling this phenomenon through tailored synthesis. Hence, we set up synthetic methodologies to access a series of thiophene-fused helicenes with a well-defined positioning of the sulfur atoms, which control the occurrence of conducting, linearly conjugated as well as disrupted, cross-conjugated pathways. We describe these synthetic strategies and relate the expected electronic transport through our molecules to three key variables: a) the exo-/endo-topology of the S atom within the ring; b) the parity (odd/even) of the overall number of rings conforming to the helicene; and c) the size of the circuit. This series ranks from [7] to [11] fused rings, having both exo-, endo-, or mixed exo-endo-topology. Comparison of homologous dithiahelicenes with size-tunable highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energies allows us to isolate the key variable of the bond topology from other electronic properties and face the study of QI in helically conjugated molecules. Understanding and tuning the conductance in such molecular solenoids is the main purpose of this work.

Visible light-induced Mallory reaction of tertiary benzanilides via iminium intermediates

The Mallory reaction, which involves the photocyclization of stilbenes/diarylethenes and their analogues into polycyclic aromatics, is of significant synthetic importance. However, its application to tertiary benzanilides has not been explored to date. Besides, most of the reported Mallory reactions require ultraviolet irradiation. In this study, we show the first Mallory reaction of tertiary benzanilides promoted by visible light via iminium intermediates formed in situ from tertiary benzanilide, Tf2O (triflic anhydride) and pyridine. UV/vis absorption spectroscopy combined with density functional theory (DFT) calculations revealed that the formation of the iminium intermediate decreased the HOMO-LUMO energy gap, thereby enhancing visible light absorption. This study provides a rapid and practical approach for the preparation of the phenanthridinone skeleton and provides a new idea for the design of new visible light photoswitches.

Reaction of 1-acetonaphthones with anilines and elemental sulfur: rapid construction of 1-anilinonaphtho[2,1-b]thiophenes

1-Anilinonaphtho[2,1-b]thiophenes could be conveniently synthesized from a three-component reaction of 1-acetonaphthones with anilines and elemental sulfur under catalyst-free simple heating conditions.