Regioselective Synthesis, Crystallographic Characterization, and Electrochemical Properties of Pyrazole‐ and Pyrrole‐Ring‐Fused Derivatives of Y₂@C_3v(8)‐C₈₂

Abstract

Chemical modification of endohedral metallofullerenes (EMFs) is an efficient strategy to realize their ultimate applications in many fields. Herein, we report the highly regioselective and quantitative mono‐formation of pyrazole‐ and pyrrole‐ring‐fused derivatives of the prototypical di‐EMF Y2@C3v(8)‐C82, that is, Y2@C3v(8)‐C82(C13N2H10) and Y2@C3v(8)‐C82(C9NH11), from the respective 1,3‐dipolar reactions with either diphenylnitrilimine or N‐benzylazomethine ylide, without the formation of any bis‐ or multi‐adducts. Crystallographic results unambiguously reveal that only one [6,6]‐bond out of the twenty‐five different types of nonequivalent C−C bonds of Y2@C3v(8)‐C82 is involved in the 1,3‐dipolar reactions. Our theoretical results rationalize that the remarkably high regioselectivity and the quantitative formation of mono‐adducts are direct results from the anisotropic distribution of π‐electron density on the C3v(8)‐C82 cage and the local strain of the cage carbon atoms as well. Interestingly, electrochemical and theoretical studies demonstrate that the reversibility of the redox processes, in particular the reversibility of the reductive processes of Y2@C3v(8)‐C82, has been markedly altered upon exohedral functionalization, but the oxidative process was less influenced, indicating that the oxidation is mainly influenced by the internal Y2 cluster, whereas the reduction is primarily associated with the fullerene cage. The pyrazole and pyrrole‐fused derivatives may find potential applications as organic photovoltaic materials and biological reagents.

Lewis Acid‐Catalyzed Substituted spiro 4‐thia‐1,2,6,9 tetraazaspiro[4.4]non‐2‐ene‐7,8‐diones via 1,3‐dipolar [3+2]cycloaddition

“…Hydrazonoyl chlorides are used as convenient precursors for in situ generation of nitrilimine 1,3-dipolars which are versatile building blocks for construction of nitrogen heterocycles and extensively studied in organic synthesis for their fascinating applications as reactive intermediates. [15][16][17][18][19][20][21][22] They are particularly useful in construction of spiro thiadiazole frameworks through 1,3-dipolar [3 + 2] cycloaddition mechanism. In literature, efficient methods for the construction of spiro 4-thia-1,2,6,9tetraazaspiro[4.4]non-2-ene-7,8-dione ring structures are scarcely discussed.…”

A Study of [3+2] Cycloaddition Reaction of Hydrazonoyl Chloride and β‐Oxodithioester Under Lewis Acid Catalysis: Stereoselective Synthesis of (Z)‐1,3,4‐Thiadiazol‐2(3H)‐Ylidenes.

“…Hydrazonoyl chlorides (RC(Cl)=N‐NHR′) are important class of compounds and also useful building blocks for synthesis of a variety of arylazaheterocycles [1] . In the presence of a base, hydrazonoyl chlorides convert into nitrilimines, which are highly reactive 1,3‐dipoles [2] and participate in 1,3‐dipolar cycloaddition reactions with a variety of dipolarophiles such as alkenes, alkynes, carbonyls, thiocarbonyls, nitriles etc ., to give five membered azaheterocycles as shown in Scheme 1. In literature, however, similar 1,3‐dipolar cycloaddition reactions of nitrilimines are also known under acid catalysis and the examples are: i) synthesis of spiropyrazoles by reaction of nitrilimines with alkenes under copper nitrate catalysis [3] and ii) Preparation of dihydropyrazoles by reaction of nitrilimines with alkenes using magnesium bis(trifluoromethanesulfonimide) as a catalyst [4] .…”

Advances in Regioselective Functionalization of Endohedral Metallofullerenes†

“…Later, in 2020, Cong, Lu, Jin and coworkers reported the functionalizetion of another C 82 fullerene cage, Y 2 @ C 3 v (8)‐C 82 . [ 30 ] Scheme 3b shows the [3+2] cyclization between 1,3‐dipolar species 14’ and 16’ , derived from precursors 14 and 16 , and Y 2 @ C 3 v (8)‐C 82 to prepare 15 and 17 , respectively with high regioselectivity. There are also reports [ 31‐32 ] about chemical functionalization on Y@ C s (6)‐C 82 (three isomers), Th@ C 3 v (8)‐C 82 (three isomers) and U@ C 2 v (9)‐C 82 (four isomers), indicating relatively high regioselectivity as there are so many possibilities for mono‐adducts.…”