Synthesis and Transformations of 5‐Chloro‐2,2′‐Dipyrrins and Their Boron Complexes, 8‐Chloro‐BODIPYs

Abstract

Symmetric dipyrrylketones 1a,b were synthesized in two steps from the corresponding α-free pyrroles, by reaction with thiophosgene followed by oxidative hydrolysis under basic conditions. The dipyrrylketones produced the corresponding 5-chloro-dipyrrinium salts or 5-ethoxy-dipyrrins on reaction with phosgene or Meerwein’s salt, respectively. Boron complexation of the dipyrrins afforded the corresponding 8-functionalized BODIPYs (borondipyrromethenes) in high yields. The 5-chloro-dipyrrinium salts reacted with methoxide or ethoxide ions to produce monopyrrole esters, presumably via a 5,5-dialkoxy-dipyrromethane intermediate. In contrast, 8-chloro-BODIPYs underwent a variety of nucleophilic substitutions of the chloro group in the presence of alkoxide ions, Grignard reagents, and thiols. In the presence of excess alkoxide or Grignard reagent, at room temperature or above, substitution at the boron center also occurred. The 8-chloro-BODIPY was a particularly useful reagent for the preparation of 8-aryl-, 8-alkyl-, and 8-vinyl-substituted BODIPYs in very high yields, using Pd0-catalyzed Stille cross-coupling reactions. The X-ray structures of eleven BODIPYs and two pyrroles are presented, and the spectroscopic properties of the synthesized BODIPYs are discussed.

Synthesis and regioselective functionalization of perhalogenated BODIPYs

“…10 Such halogenated derivatives can be the precursors of a wide range of functionalized BODIPY dyes for various applications, via Pd(0) catalyzed cross-coupling reactions (e.g., the Suzuki, Stille, Heck or Sonogashira reactions) and/or substitution reactions with C-, N-, O-, or S-nucleophiles. 11 On the other hand, halogen groups can be selectively introduced into the 3,5-positions, 10a the 2,6-, 7,12 1,7-, 13 and 8-position 14 , allowing the subsequent introduction of various functional groups to specific positions by subsequent Pd(0) cross-coupling reactions or/and substitution reactions. The platforms with 3,5-halogens 10a or/and 8-halogens 14 have attracted considerable interest due to the large distribution of the HOMO and LUMO at the 3,5-positions and 8-position, respectively.…”

“…11 On the other hand, halogen groups can be selectively introduced into the 3,5-positions, 10a the 2,6-, 7,12 1,7-, 13 and 8-position 14 , allowing the subsequent introduction of various functional groups to specific positions by subsequent Pd(0) cross-coupling reactions or/and substitution reactions. The platforms with 3,5-halogens 10a or/and 8-halogens 14 have attracted considerable interest due to the large distribution of the HOMO and LUMO at the 3,5-positions and 8-position, respectively. 1d The first 3,5-dichloro-BODIPY was reported in 2005 10a and 8-halogenated BODIPYs were reported recently, prepared by treating dipyrroketones with POCl 3 (POBr 3 ) or COCl 2 .…”

“…The starting 8-chloro-BODIPY ( 1a ) 14a was chlorinated using TCCA in acetic acid to give 2a and 3a in 73 and 81% yields, 15 respectively. Further chlorination at the 1,7-positions was unsuccessful under a variety of conditions, including NCS/THF and TCCA/acetic acid.…”

A theoretical and experimental NMR study of BODIPY 493/503: difluoro{2‐[1‐(3,5‐dimethyl‐2H‐pyrrol‐2‐ylidene‐N)ethyl]‐3,5‐dimethyl‐1H‐pyrrolato‐N}boron

“…Its X-ray structure ( Figure 2) has been reported thrice under the code JEHFUX (+01 and +02). [28][29][30][31] In the solid state, the molecule loses the symmetry planes and the fourteen C atoms are different (space group C 1 ). Actually, the symmetry is quasi-C s because the only difference between both faces is because of the H atoms of the Me12 (one of the F atoms is on the same side than one H while the other is on the same side of two H atoms).…”

Thiophosgene

“…(F) In the synthesis of BODIPYs, Wang et al 11 used the formation of dipyrrylketones 22 as the key step; such compounds were obtained in two stages: first, the reaction of pyrrole derivatives 20 and thiophosgene to get the corresponding dipyrrylthioketones 21 in 40 and 43% yield and then a subsequent oxidative hydrolysis.…”