1. Synthesis of Heterocyclic Rings 2 (Cyclization at double bonds)

2. Baldwin's rules for ring closures

3. Reactions of Carbonyl Compounds
Aldehydes and Ketones undergo addition reactions
Acids and their derivatives undergo substitution reactions

4. Intramolecular Nucleophilic Addition to Carbonyl Groups Hinzberg Synthesis of Thiophene

5. Pall-Knorr Synthesis of Furane

6. Pall-Knorr Synthesis of Pyrrole

8. Synthesis of indole

9. Synthesis of Benzofurane

10. Synthesis of Isoxazole

11. Cyclization onto an ortho position of a benzene ring o-position acts as a nucleophile

12. Cyclization onto the ortho position of a phenyl ring more examples

15. Reaction to Other double bonds (C=S, C=N, C=C)