Oxidative Ring Closure and Metal Triggered Ring Opening: Syntheses of Macrocyclic and Linear Hexapyrroles

A C6F5-substituted hexapyrrane (1) was
synthesized in one step. Oxidative cyclization of 1 with
DDQ afforded a phlorin–dipyrrin conjugate (2),
and subsequent FeCl3-assisted oxidative cleavage of 2 afforded a terminally di-α-methoxy substituted hexapyrrin
(3). On the other hand, oxidation of 1 with
FeCl3 afforded 3, a hexapyrrinone Fe3+ complex (4), and a hexaphyrin (1,1,1,1,1,0) (5). These results indicate that the oxidation of hexapyrranes
may be developed as an effective approach for the syntheses of novel
linear and macrocyclic hexapyrroles.