The First Enantiomerically Pure Triangulane (M)-Trispiro[2.0.0.2.1.1]nonane Is a σ-[4]Helicene

A remarkably high specific rotation, even at 589 nm, is shown by (M)-1, the first enantiomerically pure unbranched [4]triangulane, although it has no chromophore that would lead to any significant absorption above 200 nm. This outstanding rotatory power is in line with a helical arrangement of its σ bonds, as confirmed by high-level computations. Thus, it is appropriate to call (M)-1 a “σ-[4]helicene”, the first σ-bond analogue of the aromatic [n]helicenes.