Singly and Doubly Neo-Confused Smaragdyrins

Smaragdyrin had been an important but elusive expanded
porphyrin
until our recent first synthesis (Xie et al., J. Am. Chem.
Soc. 2018, 140, 16553). In this paper, we report
the synthesis of singly and doubly neo-confused [22]­smaragdyrin BF2-complexes 13 and 15 both as stable
smaragdyrin mutants by nucleophilic substitution reactions of 1,9-dibromo-5-mesityldipyrrin 1 with singly and doubly N-confused tripyrranes, 10 and 11, respectively. Demetalation of 13 and 15 with methanesulfonic acid furnished singly and
doubly neo-confused [22]­smaragdyrin free bases 16 and 18, respectively, both as air-sensitive porphyrinoids. These
neo-confused [22]­smaragdyrin free bases display characteristic properties
such as decreased diatropic ring current, regioselective diprotonation
at the inner α-carbon of the neo-confused pyrrole to give 16H22+ and 18H22+, and
smooth oxygenation at the inner α-position of the neo-confused
pyrroles, giving neo-confused [22]­oxosmaragdyrin 17 and
doubly neo-confused [24]­dioxosmaragdyrin Cu­(II) complex 19Cu via metalation of 18 with CuCl2 in the presence
of NaOAc. Finally, demetalation of 19Cu with methanesulfonic
acid gave the corresponding doubly neo-confused [24]­dioxosmaragdyrin 19.