Functionalization of 3,5,8-Trichlorinated BODIPY Dyes

Catalytic hydrogenation
of dibenzyl 5-dipyrroketone-2,9-dicarboxylates
followed by decarboxylative iodination affords a 2,9-diiododipyrroketone
which gives a 2,5,9-trichlorodipyrromethene hydrochloride after nucleophilic
addition/elimination, with adventitious chloride to replace the two
iodide groups. Treatment with BF3·Et2O
gives a 3,5,8-trichloro-BODIPY that readily undergoes regioselective
Stille coupling at the 8-position, or homo/mixed couplings at the
3,8- or 3,5- and 8-positions. Stepwise and controlled replacement
of the 3,5- and 8-chlorine atoms using Stille reagents results in
formation of a completely unsymmetrical trisubstituted BODIPY. Several
examples of unsymmetrical BODIPYs were synthesized and characterized
using this methodology. Structure features of new BODIPYs are discussed
within the context of 14 new X-ray structures, and photophysical parameters
of all new BODIPY compounds are reported and discussed.