FUNCTIONALIZATION OF CORROLES - FORMYLCORROLES

Porphyrins and metalloporphyrins can be readily functionalized at the meso-(5,10,15,20)-positions by using a variety of reagents, the Vilsme ier formylation reaction being universally regarded as the prototypica l example. On the other hand, the literature shows that corroles and m etallocorroles are unusually resistant to most functionalization proce dures which are common to porphyrins. The first example of peripheral functionalization of the corrole ring is now reported. Octamethylcorro le 1 readily reacts with the Vilsmeier reagent (POCl3/DMF), but the pr oduct is the 10-dimethylaminomethene derivative 2, and not the expecte d meso-formyl derivatives 3 or 4, as confirmed by a single crystal X-r ay crystallographic study. Corrole 5, where the 10-meso-position is su bstituted, affords the similar product 6. When the reaction is extende d to corrole 7 two different products, 8 and 9, are obtained wherein t he substitution is performed at both 5- and 10-meso-positions. Unlike the case of porphyrins, no reaction occurs at the beta-unsubstituted p yrrolic positions. Coordination of cobalt to the dimethylaminomethenyl corroles 2 and 5 causes both metalation and tautomerization/hydrolysis to afford the originally targeted meso-formylcorrolato complexes in a lmost quantitative yields. Attempts to formylate cobalt complex 14 usi ng TFA/trimethylorthoformate affords the corresponding beta-formyl com plexes 15 and 16, the ratio of which depends on the reaction time. mes o-Formylcorroles are also obtained by way of a new direct synthesis, d escribed herein, using a prefunctionalized a,c-biladiene 22.