SEARCH Articles Figures Tables Four- and Five-membered Ring Compounds Four-membered Four-membered ring compounds photochemical reactions Four-membered ring compounds strain energy Four-membered ring compounds synthesis Heterocyclic compounds four-membered ring opening Heterocyclic compounds four-membered ring, formation Heterocyclic compounds four-membered rings Imine compounds four-membered rings Ring compounds, structure four-membered Sulfur compounds four-membered rings