SEARCH Articles Figures Tables 5-Membered rings heteroatoms 6- membered systems Containing Heteroatoms Containment system Five Heteroatoms Five-Membered Rings One Heteroatom Five-membered ring Five-membered ring systems heteroatoms Five-membered ring systems reactions Five-membered rings heteroatoms Heteroatom Ring Systems Heteroatom-containing Heteroatom-containing systems Heteroatomic Rings Ring system five-membered Ring systems reactions Rings containing One Heteroatom System containing