Templating photodimerization of trans-cinnamic acids with cucurbit[8]uril and gamma-cyclodextrin.

Cucurbit[8]uril and gamma-cyclodextrin are able to align two olefin molecules in a head-head fashion within their large cavities. Excitation of such templated olefins results in syn head-head cyclobutanes in nearly quantitative yields. The methodology revealed here works with trans-cinnamic acids that do not dimerize either in solution or in the solid state and with the ones that yield only anti head-tail dimer in the solid state. [reaction: see text]