A silyl substituent dictates the pathway of a concerted electrocyclic ring-opening of cyclobutene

The previous, studies on rhodium chemistry directed us to investigate the substituent effect of silicon on an electrocyclic ring-opening reaction of cyclobutene. It was discovered that a silyl substituent accelerates the reaction and prefers inward rotation, giving the Z-isomer. These intriguing effects were explained by the electron-accepting interactions between the low-lying sigma* orbital of the silicon atom and the HOMO orbital of the opening cyclobutene system, possible only in the inward transition state. On the basis of this finding, a novel method for the stereoselective synthesis of functionalized 1,3-butadiene derivatives from cyclobutenones was developed.