Synthesis of a doubly SO₂-fused phlorin: Tuning the structure and properties by the SO₂ groups

Abstract

A doubly SO2-fused phlorin 4 has been synthesized by the [2 + 2] condensation of dipyrromethanecarbinol 2 and SO2-fused dipyrromenthane 3 in the presence of TFA, followed by DDQ oxidation. The SO2-fused phlorin 4 has been characterized by absorption, fluorescence, mass and NMR spectra, as well as X-ray analysis. Compared to the [Formula: see text]-unsubstituted phlorin 5, the SO2-fused phlorin 4 exhibits a red-shifted absorption spectrum (around 12 nm), a more distorted molecular conformation, as well as nice photostability even with an electron-donating meso-3,5-di-tert-butylphenyl group. The titration of 4 and 5 with TBAF has been monitored by absorption spectroscopy. The deprotonated phlorin 4 shows a peak at 870 nm which is red shifted by 26 nm compared to that of deprotonated 5.

Loading Phlorins with Fullerenes by a [4 + 2]-Cycloaddition Reaction: Regulation of the Regioselectivity by Pyrrole Linkage Modes

“…The slight optimization improves the TFA-catalyzed [2 + 2]-condensation reactions of sulfolenodipyrromethane and common dicarbinol or the N-confused one. After oxidation with DDQ, the yield of the normal sulfolenophlorin 1 (dark green powder) has been improved up to 47% over the reported 27%, and the N-confused one 2 was obtained as a dark green powder with a yield of 33%. The constituent of new compound 2 was characterized by the positive mode of HR-ESI-MS (Figure S20), of which a pseudomolecular ion [M + H] + at m / z 1179.2665 is observed, indicating the molecular formula of C 62 H 44 F 10 N 4 O 5 S 2 .…”

“…The C–N–C angles also confirm the location of normal NH-type pyrroles (angle around 110°) and imino-type ones (angle under 107°). The confused pyrrole unit is oxidized to lactam with NH pointing outward, which initiates the intermolecular H-bonds (O···H–N) to give a dimeric architecture (Figure ), resembling those of the reported N-confused phlorins. , The presence of the lactam unit regulates the number of the inner protons to two (NH + CH) with four inner H-bonds, with respect to the three inner NHs with two inner H-bonds in normal phlorin 1 . The lack of one inner proton and the resulting less steric repulsion enable 2 to display more planar conformation compared to 1 .…”

“…An upscaling preparation for 1 by using sulfolenodipyrromethane (89 mg, 0.174 mmol) and common dicarbinol (120 mg, 0.174 mmol) as starting materials gave 1 (61 mg) as a dark green powder in 30% yield: mp > 350 °C; 1 H NMR (400 MHz, CD 2 Cl 2 ) δ 7.66 (t, J = 1.6 Hz, 1H, p -ArH), 7.33 (d, J = 1.6 Hz, 2H, o -ArH), 7.22 (m, 6H, Ph-H), 7.09 (m, 4H, Ph-H), 6.97 (d, J = 4.1 Hz, 1H, Py-H), 6.94 (d, J = 4.1 Hz, 1H, Py-H), 3.83 (s, 4H, CH 2 ), 3.423 (s, 4H, CH 2 ), 1.38 (s, 18H, CH 3 ). The data are consistence with the reported one …”

“…Thus, the sulfolenopyrrole-based phlorins are promising candidates to develop the functionalized phlorins. The structure–reactivity relationship of the sulfolenophlorins in [4 + 2]-cycloaddition reaction has also attracted our interest, in that the handful examples on the cycloaddition reaction of sulfolenopyrrole-based porphyrins commonly exhibited no regio-selectivity toward annulation and afforded statistic cycloaddition products. − In the early works, changing the pyrrole linkage mode (e.g., α,α and α,β in Figure ) effectively regulates the resulting reactivity toward chemical transformation. − Hence, in this work, the normal (α,α) sulfolenophlorin 1 and N-confused (α,β) sulfolenophlorin 2 have been prepared to study the functionalization of phlorin with fullerene and explore the effect of pyrrole linkage on the [4 + 2]-cycloaddition reaction of masked phlorindienes. As a result, phlorin 1 contains two sufolenopyrrole units with identical reactivity upon tautomerization and undergoes stepwise [4 + 2]-cycloaddition with fullerenes, giving the mono and bis-fullerene adducts at 140 °C.…”

“…The sulfolenopyrroles are electron-deficient and can stabilize the resulting phlorin in our early report. 31 Simultaneously, the diene-masked sulfolenopyrrole can trap dienophiles under thermo-conditions by the [4 + 2]-cycloaddition reaction to achieve peripheral functionalization. Thus, the sulfolenopyrrole-based phlorins are promising candidates to develop the functionalized phlorins.…”