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

<p>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.</p>