Improved Synthesis and Enhanced Reactivity of X-BODIPYs

Abstract

F-BODIPYs are most known for their high thermal and photochemical stability, being quite chemically robust and having tunable fluorescence properties. This thesis focuses on three general areas of BODIPY chemistry: the synthesis of F-BODIPYs; substitution at the boron centre; and deprotection of BODIPY compounds to afford the parent dipyrrin after removal of the boron centre.

An improved methodology for the synthesis of F-BODIPYs from dipyrrins and bis(dipyrrin)s has been developed. This strategy employs lithium salts of dipyrrins as intermediates that are then treated with only 1 equiv of boron trifluoride diethyl etherate to obtain the corresponding F-BODIPYs. This scalable route to F-BODIPYs renders high yields with a facile purification process involving merely filtration of the reaction mixture through Celite in many cases.

The first Cl-BODIPYs have been synthesized in high yields from the reaction of dipyrrins with boron trichloride under air- and moisture-free conditions. These are a new class of BODIPY that enable extremely facile substitution at boron compared to their analogous F-BODIPYs, opening up a new pathway to BODIPYs functionalized at boron. Another method for the synthesis of Cl-BODIPYs has also been developed, starting from the F-BODIPY and simply treating it with boron trichloride. Cl-BODIPYs are exploited as synthetic intermediates generated in situ for the overall conversion of F-BODIPYs to O- and C-BODIPYs in high overall yields using a mild one-pot procedure. This route enables F-BODIPYs to be transformed into derivatives that are not accessible via the direct route and has led to the formation of chiral O-BODIPYs and the study of their spectroscopic properties.

The reactivity of F-BODIPYs with various boron trihalides has been investigated and has shown that activation occurs. The treatment of the activated F-BODIPY with a nucleophile affects facile substitution at boron; however, using water as the nucleophile promotes deprotective removal of the –BF2 moiety and thereby desirable production of the corresponding parent dipyrrin salt in quantitative yield under extremely mild conditions.