Xavier Creary, University of Notre Dame, Indiana, USA, has made a square-shaped carbene, 3-trimethylsilylcyclobutylidene by pyrolysis of a sodium salt derivative of 3-trimethylsilylcyclobutanone. Labeling studies reveal how this unstable species undergoes a rearrangement to form what looks like a folded square with a bridge. This occurs through a 1,3-hydrogen migration to the carbenic center rather than the suspected 1,3-silyl migration.
Silyl groups have been well studied as tools for controlling reactions and rearrangements, but on this occasion they seem not to be the group orchestrating the movement.
- 3-Trimethylsilylcyclobutylidene. The gamma-Effect of Silicon on Carbenes,
J. Am. Chem. Soc. 2013.