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.