A Dipyrrin Programmed for Covalent Loading with Fullerenes

Abstract

We describe here a di‐(β,β′‐sulfoleno)pyrrin programmed for efficient and specific β,β′‐functionalization via [4+2] cycloaddition reactions. At 120 °C and in the presence of an excess of C60‐fullerene the di‐(β,β′‐sulfoleno)pyrrin decomposed cleanly, furnishing a di‐(β,β′‐fullereno)pyrrin and the corresponding monofullereno‐dipyrrin in an overall yield of 96 %. Hence, relatively mild thermolysis of the di‐(β,β′‐sulfoleno)pyrrin induced stepwise extrusion of two equivalents of SO2, producing highly reactive dipyrrin‐β,β′‐diene intermediates readily, providing a very effective path to [4+2]‐cycloadducts. As presented here by the example of the covalent attachment of C60‐fullerene units, a convenient general methodology for the efficient synthesis of covalent dipyrrin β,β′‐cycloadducts is made available.

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

“…The two sharp signals for CH 2 groups correlate with carbons at 55.3 and 55.9 ppm, typical chemical shift values for the carbon linked to the SO 2 group. By contrast, the two broad ones correlate with typical fullerene attached carbons at 39.8 and 40.2 ppm, , confirming the structure of 1-C60 . With the introduction of two fullerenes, the molecule ( 1-2C60 ) becomes symmetric and affords simplified resonances as those of 1 .…”

“…Indeed, the 1 H, 13 C-HSQC spectrum of 2-C60 shows the coupling from these broad signals to the fullerene-modified carbons, owing to the very similar chemical shift values as those for the fullereno-modified CH 2 in 1-C60, 1-2C60, or the early reports (Figure S16). 33,34 Furthermore, in the 1 H, 13 C-HMBC spectrum, the two broad singlets correlate with the unsaturated carbons on fullerene at 155.6 ppm and the saturated ones at 65.9 ppm typical chemical shift values for the carbons at the [6,6]-bond of fullerene after cycloaddition. 34 Finally, the couplings from the CH 2 groups to the pyrrole carbons in the HMBC spectrum of 2-C60 verify the location of fullerene (Figure S17).…”

“…33,34 Furthermore, in the 1 H, 13 C-HMBC spectrum, the two broad singlets correlate with the unsaturated carbons on fullerene at 155.6 ppm and the saturated ones at 65.9 ppm typical chemical shift values for the carbons at the [6,6]-bond of fullerene after cycloaddition. 34 Finally, the couplings from the CH 2 groups to the pyrrole carbons in the HMBC spectrum of 2-C60 verify the location of fullerene (Figure S17). The sharp signals of CH 2 show couplings with the carbons at 125.0 and 128.3 ppm, which are almost identical to those at the normal NH-type sulfolenopyrrole in 2.…”

“…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.…”

Aromatic Ring-Fused Dipyrrins: Programmed [4 + 2]-Cycloaddition Pathway with Regio-selectivity upon Alkylamino-Substitution

“…The unique sulfolenopyrrole features a sulfolene unit fused at β,β-positions, − and can undergo the cheletropic reaction to extrude SO 2 under heating. As a result, the reactive s-cis type diene will be generated in situ, which can trap the dienophiles through the [4 + 2]-cycloaddition reaction to build the six-member ring. ,− Incorporation of sulfolenopyrrole(s) into oligopyrroles proves to be an efficient way for peripheral annulations through [4 + 2] cycloaddition. − In 2018, Kräutler, Li, and co-workers prepared sulfolenodipyrrin, to which the fullerenes were efficiently loaded through a programmed [4 + 2]-cycloaddition reaction . Thus, sulfolenodipyrrins are expected to be potential building blocks in the construction of aromatic ring-fused dipyrrins.…”