Double helices of dissymmetrical α,α'-disubstituted tripyrrins.

Dissymmetrical α,α'-disubstituted tripyrrins have been prepared using a modified synthetic protocol. Tripyrrin 2a bearing 3,5-bis(trifluoromethyl)phenyl and 4-methoxyphenyl moieties showed an anti -type dimer arrangement in the solid state. In contrast, syn -type dimers were observed for tripyrrin 2b bearing 3,5-bis(trifluoromethyl)phenyl and 3,5-di- t -butylphenyl moieties. In addition, proton-exchange NH tautomerization was observed in 2b.