Linear and Cyclic Amides with a Thiophene Backbone: Ultrasound-Promoted Synthesis and Crystal Structures

A full synthetic study of linear and cyclic thiophene
oligoamides
has been carried out. The combination of an ultrasonic technique to
diminish the intramolecular backfolding of longer oligoamide chains,
therefore enhancing the accessibility of the carboxylic acid, and
T3P as coupling reagent led to shorter reaction time and higher yields
for both linear and cyclic oligoamides. By controlling the degree
of dilution, macrocyclic amides with different sizes can selectively
be prepared. Different crystal structures of cyclic thiophene oligoamides
were also analyzed.