title: Synthesis of 3,8-dichloro-6-ethyl-1,2,5,7-tetramethyl-BODIPY from an asymmetric dipyrroketone and reactivity studies at the 3,5,8-positions.
abstract: The asymmetric BODIPY 1 a (BODIPY=4,4-difluoro-4-bora-3a,4a-diaza-s-indacene), containing two chloro substituents at the 3,8-positions and a reactive 5-methyl group, was synthesized from the asymmetric dipyrroketone 3, which was readily obtained from available pyrrole 2 a. The reactivity of 3,8-dichloro-6-ethyl-1,2,5,7-tetramethyl-BODIPY 1 a was investigated by using four types of reactions. This versatile BODIPY undergoes regioselective Pd(0) -catalyzed Stille coupling reactions and/or regioselective nucleophilic addition/elimination reactions, first at the 8-chloro and then at the 3-chloro group, using a variety of organostannanes and N-, O-, and S-centered nucleophiles. On the other hand, the more reactive 5-methyl group undergoes regioselective Knoevenagel condensation with an aryl aldehyde to produce a monostyryl-BODIPY, and oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) gives the corresponding 5-formyl-BODIPY. Investigation of the reactivity of asymmetric BODIPY 1 a led to the preparation of a variety of functionalized BODIPYs with λmax of absorption and emission in the ranges 487-587 and 521-617 nm, respectively. The longest absorbing/emitting compound was the monostyryl-BODIPY 16, and the largest Stokes shift (49 nm) and fluorescence quantum yield (0.94) were measured for 5-thienyl-8-phenoxy-BODIPY 15. The structural properties (including 16 X-ray structures) of the new series of BODIPYs were investigated.
authors.affiliation: Department of Chemistry, Louisiana State University, Baton Rouge, LA, 70803 (USA).
authors.forename: Ning
authors.initials: N
authors.lastname: Zhao
authors.forename: M Graça H
authors.initials: MG
authors.lastname: Vicente
authors.forename: Frank R
authors.initials: FR
authors.lastname: Fronczek
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Smith
mesh_terms: D016227:Benzoquinones / Q000737:chemistry; D001896:Boron Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry*; D054879:Halogenation; D007659:Ketones / Q000737:chemistry; D008745:Methylation; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011758:Pyrroles / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D016227:Benzoquinones; D001896:Boron Compounds; D005456:Fluorescent Dyes; D007659:Ketones; D011758:Pyrroles; C000928:dichlorodicyanobenzoquinone
keywords: BODIPY; Pd0-catalyzed coupling; addition/elimination; fluorescence; oxidation; substitution