Supramolecular assistance of [2+2] Photocycloaddition for crossphotodimerization

[2+2] Photocycloaddition (PCA) of alkenes is an important reaction as it is used in several areas of fundamental and applied research. Due to its significance, there are numerous articles and reviews in chemical literature that document various aspect of this reaction-such as application in synthesis, photopolymerization, materials research, etc. Despite its importance, the vast majority of the reports are focused on the reaction between identical alkenes (homo-dimerization), while PCA between non-identical alkenes (cross-dimerization) has been grossly under-explored. In this review we have complied the reports on cross-dimerization reactions affected through supramolecular methods, which can be broadly classified based on two broad approaches: (a) crystal-engineering or (b) templation in solution or slurry. Both methods are based on the utilization of favorable intermolecular interaction between non-identical alkenes, and the use of a templating agent that promotes heteroalkene arrangement in the ground state, which, upon photoexcitation yield the cross-dimer selectively.