Unprecedented photochemical rearrangement of an open-cage C60 derivative.

Upon irradiation of a sulfoxide C60 derivative with a 17-membered-ring opening, rearrangement of the carbon framework took place to give an unprecedented lactone C60 derivative with a 14-membered-ring opening, whose structure was unambiguously determined by single crystal X-ray analysis. This reaction is completely different from that of the previously reported sulfoxide C60 and C70 derivatives with a 13-membered-ring opening.