148
Y. Kubota
of 5-carboxylic furopyrroles, followed by reaction with 1 equivalent of symmetrical or unsymmetrical 5-formyl furopyrroles and POCl 3 and subsequent boroncomplexation (Fig. 5.31, Route4) (Umezawa et al. 2008, 2009). Decarboxylation of
4H-furo[3,2-b]pyrrole-5-carboxylic acid by perfluorocarboxylic acid and subsequent
reaction with corresponding perfluorocarboxylic anhydride and boron complexation gives meso-perfluoroalkyl substituted BODIPY dyes (Fig. 5.31, Route1) (Li
et al. 2018a). Similarly, benzofuran- and naphtho[1,2-b]furan-fused BODIPY dyes
are synthesized from the corresponding ring-fused pyrrole-5-carboxylic acids (Li
et al. 2018b). Meso-CF 3 substituted furan-fused BODIPY dyes are also synthesized
from 4H-thieno[3,2-b]pyrrole-5-carboxylic acid by using the same method (Awuah
et al. 2011). Ring-fused pyrrole-5-carbaldehydes can be obtained by heating a TFA
solution of ring-fused pyrrole-5-carboxylic acid, followed by reaction with triethyl
orthoformate (Fig. 5.31, Route3) (Umezawa et al. 2009). The reaction of ring-fused
pyrrole-5-carbaldehyde with POCl 3 , followed by boron complexation, also furnishes
meso-unsubstituted BODIPY dyes (Fig. 5.31, Route5) (Tanaka et al. 2013).
Method (2) consists of regioselective introduction of aryl groups into the
BODIPY core via Pd-catalyzed coupling and subsequent intramolecular cyclization. In 2012, Shinokubo and co-workers reported the formation of phenanthrenefused BODIPY by a Suzuki coupling–oxidative cyclization sequence (R
1
= Br,
R
2
= H, X = B(OH) 2 ). The introduction of biphenyl groups at the β-positions
of the BODIPY core via Suzuki coupling, followed by oxidative cyclization
using [Bis(trifluoroacetoxy)iodo]benzene (PIFA) and BF 3 ·OEt 2 , yielded the target
BODIPY dye (Fig. 5.32) (Hayashi et al. 2012). Dithienyl BODIPY dyes are similarly synthesized by a Suzuki coupling–oxidative cyclization sequence (R
1
= Br
or I, R
2
= H, X = Bpin) (Heyer et al. 2014). Additionally, indole-fused BODIPY
dyes are synthesized through a regioselective decarboxylative direct C-H arylation–
Cadogan reaction sequence (R
1
= H, R
2
= H, X = CO 2 H) (Luo et al. 2014). The
decarboxylative cross-coupling reaction of 2-nitrobenzoic acid with a meso-phenylsubstituted BODIPY dye in the presence of Pd(OAc) 2 , PCy 3 ·HBF 4 , Ag 2 CO 3 , and 4
Fig. 5.32 Synthesis of [b]-fused BODIPY dyes by regioselective introduction of aryl groups via
Pd-catalyzed coupling and subsequent intramolecular annulation
Y. Kubota
of 5-carboxylic furopyrroles, followed by reaction with 1 equivalent of symmetrical or unsymmetrical 5-formyl furopyrroles and POCl 3 and subsequent boroncomplexation (Fig. 5.31, Route4) (Umezawa et al. 2008, 2009). Decarboxylation of
4H-furo[3,2-b]pyrrole-5-carboxylic acid by perfluorocarboxylic acid and subsequent
reaction with corresponding perfluorocarboxylic anhydride and boron complexation gives meso-perfluoroalkyl substituted BODIPY dyes (Fig. 5.31, Route1) (Li
et al. 2018a). Similarly, benzofuran- and naphtho[1,2-b]furan-fused BODIPY dyes
are synthesized from the corresponding ring-fused pyrrole-5-carboxylic acids (Li
et al. 2018b). Meso-CF 3 substituted furan-fused BODIPY dyes are also synthesized
from 4H-thieno[3,2-b]pyrrole-5-carboxylic acid by using the same method (Awuah
et al. 2011). Ring-fused pyrrole-5-carbaldehydes can be obtained by heating a TFA
solution of ring-fused pyrrole-5-carboxylic acid, followed by reaction with triethyl
orthoformate (Fig. 5.31, Route3) (Umezawa et al. 2009). The reaction of ring-fused
pyrrole-5-carbaldehyde with POCl 3 , followed by boron complexation, also furnishes
meso-unsubstituted BODIPY dyes (Fig. 5.31, Route5) (Tanaka et al. 2013).
Method (2) consists of regioselective introduction of aryl groups into the
BODIPY core via Pd-catalyzed coupling and subsequent intramolecular cyclization. In 2012, Shinokubo and co-workers reported the formation of phenanthrenefused BODIPY by a Suzuki coupling–oxidative cyclization sequence (R
1
= Br,
R
2
= H, X = B(OH) 2 ). The introduction of biphenyl groups at the β-positions
of the BODIPY core via Suzuki coupling, followed by oxidative cyclization
using [Bis(trifluoroacetoxy)iodo]benzene (PIFA) and BF 3 ·OEt 2 , yielded the target
BODIPY dye (Fig. 5.32) (Hayashi et al. 2012). Dithienyl BODIPY dyes are similarly synthesized by a Suzuki coupling–oxidative cyclization sequence (R
1
= Br
or I, R
2
= H, X = Bpin) (Heyer et al. 2014). Additionally, indole-fused BODIPY
dyes are synthesized through a regioselective decarboxylative direct C-H arylation–
Cadogan reaction sequence (R
1
= H, R
2
= H, X = CO 2 H) (Luo et al. 2014). The
decarboxylative cross-coupling reaction of 2-nitrobenzoic acid with a meso-phenylsubstituted BODIPY dye in the presence of Pd(OAc) 2 , PCy 3 ·HBF 4 , Ag 2 CO 3 , and 4
Fig. 5.32 Synthesis of [b]-fused BODIPY dyes by regioselective introduction of aryl groups via
Pd-catalyzed coupling and subsequent intramolecular annulation