A C 70 fragment (1) (C 28 H 14 ) was synthesized by conversion of a C 60 fragment sumanene, via ring expansion and annulation in 3 steps, the key step being the WagnerMeerwein rearrangement of a five-membered ring to a six-membered one. Both theoretical and experimental investigations exhibited the shallower bowl structure of 1, resulting in the lower bowl inversion barrier than sumanene. It was also revealed that the indenopyrene skeleton largely contributed to the physical properties of 1. Bowl-shaped π-conjugated aromatic hydrocarbons, corresponding to the fragments of fullerenes (buckybowls), have been attracting widespread interest owing to their unique chemical and physical properties.1 Buckybowls, which possess the fragment skeleton of C 60 , such as corannulene and sumanene, have been extensively studied and various unique properties have been reported. 2,3 In contrast, buckybowls bearing C 70 fragment have not drawn much attention and only few examples have been reported to date. 4 The feature of C 70 is that the presence of additional ten carbons, which connect the two C 60 -like hemispheres and provide the shallower curved structure partially than in C 60 skeleton. A simple and effective method to achieve the formation of the fragment skeleton of C 70 is the conversion of the fused five-membered ring in the fragment structure of C 60 to the fused six-membered ring, which realizes the bowl-depth change from deeper to shallower.Here we show the synthesis of a new buckybowl C 28 H 14 (1) (Figure 1), corresponding to a 40% fragment of C 70 from the C 60 fragment sumanene (2) via ring expansion and annulation, in which WagnerMeerwein rearrangement of a five-membered ring to a six-membered one was the key step.The synthetic plan from sumanene 2 to 1 is shown in Scheme 1 according to Bavin's report on the transformation from the fluorene skeleton to the phenanthrene one via Wagner Meerwein rearrangement (Scheme 1).5 Generation of benzylic carbanion by the addition of n-BuLi (150 mol %) to 2 in THF at ¹80°C, followed by the addition of aryl or heteroaryl aldehydes (150 mol %) quantitatively afforded the precursors 3a3c for the rearrangement reaction (Table 1). The WagnerMeerwein rearrangement was carried out by the reaction of 3a3c with stoichiometric p-TsOH in toluene under reflux condition, giving the benzopyrene derivative 4a4c in good yields. X-ray singlecrystal analysis of 4b confirmed its shallower curved structure
Buckybowls bearing a C 70 fragment having two alkoxy groups were synthesized and their structural and optical properties were investigated by single crystal X-ray analysis and UV-vis spectroscopy. In the synthesis of dioxole derivative 5b, the regioisomer 5c was also produced. The yield of 5c was increased by increasing the reaction temperature, indicating that the rearrangement might involve the equilibrium between the Pd(IV) intermediates through C-H bond activation.
Buckybowls of C70 fragment having two alkoxy groups were synthesized and their structural and optical properties were investigated by single crystal X-ray analysis and UV-vis spectroscopy. In the synthesis of dioxole derivative 5b, the regio isomer 5c was also produced. The yield of 5c was increased by increasing the reaction temperature, indicating that the rearrangement might involve the equilibrium between the Pd(IV) intermediates through the C-H bond activation.
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