Characterization of photocycloaddition products in the cyclobutane family using mass spectrometry and nuclear magnetic resonance

Photocycloaddition products receive much attention and are of great utility in capturing reaction intermediates and preparing natural compounds. A collection of compounds containing a cyclobutane ring was studied. This collection, produced previously in our laboratory, was divided into classes based upon putative structures and synthetic pathways. Three groups (tetrasubstituted cyclobutane derivatives, fused-ring systems and cyclo-octatetrane derivatives) having quite uncommon characteristics and supposed structures were made. The behaviors of these previously-made photocycloaddition products of similar structure were investigated using mass spectrometry, proton- (1H-), carbon- (13C-) and 2D-NMR techniques. Additionally, UV irradiation experiments were conducted to produce more photoadducts. Finally, the information acquired from the characterizations of the previously-made products was applied to identify the unknown components in the reaction mixtures of the irradiation experiments. Positive identification of the structures of these separate classes of photocycloaddition products supports a discussion of mechanistic pathways to their formation.