Computational study on photo- and thermo-reactions between tetra-tert-butyl-substituted cyclobutadiene and tetrahedrane

► Cyclobutadiene isomerizes to tetrahedrane via the HOMO-LUMO double electron excited state. ► Electronic effect of t-Bu group enables the photoreaction from cyclobutadiene to tetrahedrane. ► Steric effect between t-Bu groups plays a role to stabilize tetrahedral shape.