INVESTIGATION OF THE ONE-FLASK SYNTHESIS OF PORPHYRINS BEARING MESO-LINKED STRAPS OF VARIABLE-LENGTH, RIGIDITY, AND REDOX ACTIVITY

The reactions of 18 dialdehydes have been examined in the two-step one -flask room temperature porphyrin synthesis. Efficient alkylation meth ods were established for the reaction of diols and diacids with m-brom omethylbenzaldehyde Dialdehydes linked at the o,o'- or m,m'-positions were converted to strapped porphyrins in yields up to 25%, while the o ne p,p'-linked dialdehyde that was examined failed to give porphyrin. The resulting porphyrins bear straps joining adjacent meso-positions r ather than across the face of the porphyrin. Dialdehydes incorporating rigid groups provided improved yields in some but not all cases. The yield of strapped porphyrin exhibited a maximum at 10(-2) M reactant c oncentrations. The o,o'-strapped porphyrins exist as atropisomers thai are sufficiently stable to interconversion at room temperature to be separable chromatographically. No atropisomers of m,m'-strapped porphy rins could be separated, though some could be observed by H-1 NMR spec troscopy. For two different m,m'-strapped porphyrins, the Delta G doub le dagger values for interconversion of the atropisomers were found to be 66 and 68 kJ/mol. The outer rings in these strapped porphyrins ran ge in size from 14 to 24 atoms. Five porphyrins with bridging redox-ac tive groups (ferrocene or anthraquinone) have been prepared in one-fla sk reactions, including a porphyrin bearing one ferrocene and one anth raquinone in straps across adjacent meta-substituted phenyl sites. (C) 1997 Elsevier Science Ltd.