Refined methods for the synthesis of meso-substituted A3- and trans-A2B-corroles

Abstract

We have refined a one-pot synthesis of A₃-corroles via “3+4” condensation of an aldehyde with a pyrrole followed by macrocyclization mediated by DDQ. After thorough examination of various reaction parameters (reactivity of an aldehyde, catalyst, solvent, concentration, time etc.) we have elaborated three different sets of conditions for different types of aromatic aldehydes—highly reactive, moderately reactive and sterically hindered. Thanks to the identification of the key factors influencing the yield of bilanes and the yield of their conversion to corroles we were able to improve yields to ca. 17% for highly reactive aldehydes and ca. 13% for moderately reactive aldehydes. Altogether fourteen A₃-corroles have been prepared in 7–21% yield. 5,10,15-Trimesitylcorrole has been obtained for the first time. [2+1] Condensation between sterically hindered dipyrromethanes and aldehydes has also been refined and yields of trans-A₂B-corroles have been improved by ca. 10%.