Transition-metal-catalyzed synthesis of organophosphate-appended cyclobutanofullerenes from C60 and secondary propargylic phosphates

One‐Step Synthesis of Cyclobutene‐Annulated Fullerenes through a Cascade Reaction

“…By contrast, when 4 a was heated for 1 h at 180 °C, the intensity of the peak corresponding to 4 a decreased by 19 %, and a peak corresponding to 2 a (31 %) appeared; however, no peaks corresponding to 3 a or C 60 were observed. These results, in conjunction with those of previous studies, [3,4,6,[13][14][15][16] suggest that 2 is formed through the reaction pathway depicted in Scheme 3. The three carbon atoms of the allene moiety in allene intermediate 5 are labeled as C α , C β , and C γ , according to Scheme 3.…”

“…These results are in contrast to those obtained in a previous study, wherein the production of the corresponding cyclobutenofullerenes was quite limited under similar conditions when a secondary propargylic phosphate possessing terminal alkynes, substituted with either hydrogen or silyl groups, was included. [6] Phosphates 1 c-1 f behaved similar to 1 a in the reaction with C 60 without CuCl, producing cyclobutenofullerenes with 12-17 % yields (conv. y.: 13-40 %) (Table 1, entries 8, 10,12,14).…”

“…The molecular structure of 2 a was detailed using single-crystal X-ray crystallography, and the results are depicted in Figure 1. X-ray analysis revealed that a highly distorted cyclobutene ring with a C=C bond length of 1.349 Å was fused to the [6,6]-junction of C 60 . Additionally, the entire addendum was positioned in a nearplanar fashion.…”

“…[5] Previously, when secondary propargylic phosphates possessing terminal alkynes substituted with either hydrogen or silyl groups were included in the reaction with C 60 in the presence of a silver salt, organophosphate-appended cyclobutanofullerenes were obtained as major products instead of open-cage fullerenes. [6] Thus, we anticipate that the molecular transformation of fullerenes, including the construction of complex and diverse structures, can be achieved through a single-step cascade reaction by changing the type of transition metal and the structures of propargylic ester compounds. While conjugated cyclobutenes are of particular interest in materials science, they are difficult to study because the highly distorted structures of conjugated cyclobutenes present challenging synthetic targets.…”

“…Furthermore, an open‐cage fullerene derivative featuring an eight‐membered ring orifice can be synthesized via a one‐step cascade reaction of C 60 with a tertiary propargylic phosphate in the presence of a copper salt [5] . Previously, when secondary propargylic phosphates possessing terminal alkynes substituted with either hydrogen or silyl groups were included in the reaction with C 60 in the presence of a silver salt, organophosphate‐appended cyclobutanofullerenes were obtained as major products instead of open‐cage fullerenes [6] . Thus, we anticipate that the molecular transformation of fullerenes, including the construction of complex and diverse structures, can be achieved through a single‐step cascade reaction by changing the type of transition metal and the structures of propargylic ester compounds.…”