Substituent effect of group 14 elements on the ring-opening reaction of cyclobuteneElectronic supplementary information (ESI) available: Details of the kinetic experiment and optimized geometries of stationary points as Cartesian coordinates. See DOI: 10.1039/c004972g

A series of cyclobutenes bearing group 14 elements at the 3-position were synthesized, and their thermal ring-opening reactions were studied. Carbon-substituted cyclobutene underwent the ring-opening reaction through an outward pathway to afford the E -diene exclusively. On the other hand, the ring-opening reaction of the silyl, germyl, and stannyl substituted cyclobutenes occurred in both outward and inward directions giving a mixture of E and Z isomers. The structural features of the calculated transition state and population analysis suggested that the formation of the Z -isomer could be ascribed to the donor/acceptor interaction between the HOMO and the σ * orbital of group 14 elements. Interestingly, the order of inward preference was Si > Sn > Ge. These rotational behaviors of silyl, germyl, and stannyl substituents were explained by taking into account the energy gap and the magnitude of overlap between the σ * orbital and HOMO. A series of cyclobutenes bearing group 14 elements at the 3-position were synthesized, and their rotational behaviors in the thermal ring-opening reaction are discussed.