heteroatom in each heterocyclic ring 883 7.22.9.1.2 With two heteroatoms in one heterocyclic ring and one in the other 884 7.22.9.2 Synthesis of Compounds with a Central Five-membered Ring 885 7.22.9.2.1 With one heteroatom in each heterocyclic ring 885 7.22.9.2.2 With two heteroatoms in one heterocyclic ring and one in the other 886 875 876 Tricyclic Systems: Central Carbocyclic Ring, 5-and 6-membered Rings 7.22.9.2.3 With two heteroatoms in each heterocydic ring 886 7.22.9.3 Synthesis of Compounds with a Central Six-membered Ring 886 7.22.9.3.1 With one heteroatom in each heterocydic ring 886 7.22.9.3.2 With two heteroatoms in one heterocydic ring and one in the other 894 7.22.9.3.3 With two heteroatoms in each heterocydic ring 900 7.22.9.3.4 With more than two heteroatoms in either heterocydic ring 900 7.22.9.4 Synthesis of Compounds with a Central Seven-membered Ring 902 7.22.9.4.1 With one heteroatom in each heterocydic ring 902 7.22.9.4.2 With two heteroatoms in one heterocydic ring and one in the other 903 7.22.10 RING SYNTHESIS BY TRANSFORMATION OF ANOTHER RING 903 7.22.11 SYNTHESIS OF PARTICULAR CLASSES OF COMPOUNDS 905 7.22.11.1 Benzo-separated Purines 905 7.22.11.2 Furocoumarins and Furochromones 911 7.22.11.2.1 Synthesis using chromium carbene complexes 911 7.22.11.2.2 Other methods 912 7.22.11.3 Ellipticines 913 7.22.11.3.1 Synthesis using cydoaddition reactions 913 7.22.11.3.2 Other methods 914 7.22.11.4 Pyrroloquinolinequinone and Related Compounds 914 7.22.12 IMPORTANT COMPOUNDS AND APPLICATIONS 915 7.22.12.1 Benzo-separated Purines 915 7.22.12.2 Furocoumarins and Furochromones 916 7.22.12.3 Ellipticines 917 7.22.12.4 Pyrroloquinolinequinones and Related Compounds 917 7.22.12.5 Ergolides