Investigations into the nucleophilic meso-substitution of F-BODIPYs and improvements to the synthesis of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene.
Abstract
A series of three F-BODIPYs, with varying levels of steric crowding about the meso-position were
selected to investigate nucleophilic meso-substitution of F-BODIPYs. The synthesis of one of these
F-BODIPYs, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (totally unsubstituted dipyrrin skeleton), was
optimized to give higher yields over routine literature procedures. This modified procedure involves
oxidn. of a dipyrromethane using p-chloranil, instead of DDQ, to give a dipyrrin which is then
trapped in situ as its BF2 complex. Nucleophilic meso-alkylation of the series of F-BOIDPYs with
n-butyllithium gave meso-Bu F-BODIPYs in moderate to good yields. This work represents a new,
synthetically viable method for the synthesis of meso-alkylated F-BODIPYs. Extension of the
nucleophilic substitution methodol. to meso-arylation was possible. However, the reaction was
unselective: substitution at boron, to give the boron-diaryl C-BOIDPYs, occurred preferentially to
nucleophilic meso-substitution and thus a mixt. of products was obtained.
Citation
Crawford, Sarah M., and Alison Thompson. 2011. "Investigations into the nucleophilic meso-substitution of F-BODIPYs and improvements to the
synthesis of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene." Heterocycles 83(2): 311-322.