Photodimerization of enaminoketonatoboron difluorides

Irradiation of enaminoketonatoboron difluorides (complexes) in solution in the presence of benzophenone gave two stereoisomeric dimers: syn head-to-tail (H-T) and anti H-T. The observed stereochemical control can be understood on the basis of steric energies calculated by molecular mechanics. However, in the crystalline state the complexes selectively afforded an anti H-T dimer. X-Ray analysis of the complex confirms that this reaction proceeds according to known topochemical principles. The cyclobutane ring formed shows planar and puckered forms in the syn H-T and anti H-T dimers, respectively.