Skeletal transformation to chiral molecular nanocarbons

Three-dimensional molecular nanocarbons represent crucial building blocks for advanced carbon materials. However, the unconscious dependence of the current organic synthesis on the stepwise bond formation limits the retrosynthesis. Herein, we demonstrate that the skeletal transformation effectively solves two challenges in nanocarbon synthesis. First, the inner-bond cleavage of π-conjugated hydrocarbons realizes the rapid access to an all-sp2-carbon ten-membered ring. The subsequent ring expansion affords decagon-containing chiral gigantic nanocarbons with figure-eight or bathtub conformations consisting of up to 170 sp2-hybridized carbons. Second, the subsequent restoration of an internal double bond enables the regio- and enantio-selective synthesis of a helically twisted nanographene containing 26 six-membered rings. This chiral nanographene exhibits a homochiral porous framework consisting of π-stacked double-helical assemblies in its crystal packing. These results demonstrate that the skeletal transformation, which has so far targeted bioactive molecules, evokes a mind-change even in nanocarbon synthesis.