Bay-Substituted Thiaza[5]helicenes: Synthesis and Implications on Structural and Spectroscopic Properties

A series
of bay-substituted thiaza[5]­helicenes was synthesized
to investigate the effect of different substituents on the properties
of these helicenes. These thiaza[5]­helicenes with different substituents
were prepared in a straightforward manner through indole- and benzo­[b]­thiophene synthesis, palladium-catalyzed Suzuki coupling,
oxidative cyclization, and functional group interconversion reactions.
We investigated the impact of these different bay area substituents
compared to the unsubstituted thiaza[5]­helicene on the structural
parameters and studied the steady-state electronic spectroscopy of
these thiaza[5]­helicenes in toluene and acetonitrile. We found that
different functional groups influence the solid state structure and
spectroscopic properties, but a single substituent in the bay area
of a thiaza[5]­helicene was not enough to prevent enantiomerization
at room temperature.