Synthesis of dipyrrins bearing chirality adjacent to the conjugated skeleton — Electron-poor pyrroles exhibit dramatically reduced nucleophilicity

Abstract

With the aim of furthering our investigations into the asymmetric complexation of dipyrrinato ligands, a dipyrrin bearing a stereogenic centre directly adjacent to the conjugated skeleton was synthesized. The electron-withdrawing nature of the chiral 4-(2,2,2-trifluoro-1-hydroxyethyl)- substituent significantly reduced the nucleophilicity of corresponding pyrroles, such that 2,2′-symmetrically substituted bis(dipyrrin)s bearing this motif were inaccessible. Furthermore, solutions of mononuclear dipyrrinato complexes were found to be less stable to acid-catalyzed decomplexation than the corresponding dinuclear complexes.Key words: dipyrrin, dipyrromethene, complexation, electron-poor pyrrole, chirality.

Use ofF-BODIPYs as a Protection Strategy for Dipyrrins: Optimization of BF2Removal

“…Mp 177–180 °C; 1 H NMR (CDCl 3 , 500 MHz) δ 7.04 (s, 1H), 5.08–5.03 (m, 1H), 2.55 (s, 3H), 2.53 (s, 3H), 2.47 (d, 1H, J = 3.5 Hz), 2.39 (q, 2H, J = 7.7 Hz), 2.28 (s, 3H), 2.18 (s, 3H), 1.07 (t, 3H, J = 7.7 Hz). NMR data matches that previously reported for this compound …”

“…Mp 68−72 °C; 1 H NMR (CDCl 3 , 500 MHz) δ 6.99 (s, 1H), 6.00 (s, 1H), 2.52 (s, 3H), 2.50 (s, 3H) 24). 40 Compound 24 was prepared previously from the dipyrrin•HBr salt 40 using GP1. Mp 177−180 °C; 1 H NMR (CDCl 3 , 500 MHz) δ 7.04 (s, 1H), 5.08−5.03 (m, 1H), 2.55 (s, 3H), 2.53 (s, 3H), 2.47 (d, 1H, J = 3.5 Hz), 2.39 (q, 2H, J = 7.7 Hz), 2.28 (s, 3H), 2.18 (s, 3H), 1.07 (t, 3H, J = 7.…”

“…NMR data matches that previously reported for this compound. 40 4,4-Difluoro-1,7-diethyl-2,6-diphenyl-3,5-dimethyl-8-H-4bora-3a,4a-diaza-s-indacene (26).…”

Conversion of 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacenes (F-BODIPYs) to Dipyrrins with a Microwave-Promoted Deprotection Strategy

“…The β- and meso -unsubstitued dipyrrins 4a and 5a were also deprotected (CAUTION 4b is a sternutator). This method was applied to the unsymmetrical F -BODIPY 6a to give 6b in excellent isolated yield.…”