Download Heterocyclics - Organic Chemistry II - Lecture Slides and more Slides Organic Chemistry in PDF only on Docsity! Heterocycles Ring compounds with elements other than carbon in the ring. The most common elements to appear in heterocyclic compounds are oxygen, nitrogen and sulfur. The aliphatic heterocycles are similar to the open chain analogues, ethers, amines and sulfides. The aromatic heterocycles are similar to other aromatic compounds. docsity.com Heterocyclic Nomenclature Replacement nomenclature (IUPAC recommended 1957) Oxygen oxa Sulfur thia Nitrogen aza Lowest number assigned to the hetero atom with the highest precedence: O > S > N S thiacyclobutane O NH 1-oxa-3-azacyclopentane docsity.com O S NH N N oxetane oxacyclobutane thietane thiacyclobutane azetidine azacyclobutane azete azacyclobutadiene 1-azetine 1-azacyclobutene docsity.com O O N H O O S N H * furan oxole oxacyclopentandiene * thiophene thiole thiacyclopentandiene * pyrrole 1,3-dioxolane 1,3-dioxacyclopentane * tetrahydrofuran * pyrrolidine azacyclopentane docsity.com N O N SO N N H N N N H N N H N pyrazole imidazole 1,2,4-triazole oxazole isooxazole thiazole docsity.com 6 7 8 5 N 1 2 3 4 6 7 8 5 1 N 2 3 4 N H * quinoline * isoquinoline * indole docsity.com Aliphatic heterocyclics, chemistry Ethers Amines sulfides O conc. HBr heat BrCH2CH2CH2CH2Br HNCH3 C Cl O + CH3 C N O 2o amine docsity.com Three-membered rings undergo additions due to angle strain, eg. epoxides O O + HBr + NH3 HOCH2CH2Br HOCH2CH2NH2 docsity.com N H N H CH=O N H C N H Br pyrrole CHCl3, KOH HCN, HCl H2O (CH3CO)2O 250o CH3 O Br2, EtOH 0o BrBr Br docsity.com O furan CH3CO2NO2 O NO2 pyridine:SO3 O SO3H C6H5N2 + O N N (CH3CO)2O, BF3 O C O CH3 docsity.com O furan O CH=O O Br O HgCl O I 1. HCN, HCl 2. H2O Br2 dioxane HgCl2 CH3CO2Na I2 CH3COCl O C O CH3 docsity.com N H O H2, Ni 250o H2, Ni 50o N H O Kb = 10-14 Kb = 10-3 2o amine THF docsity.com Pyridine N N N6 pi electrons, sp2, flat aromatic, resonance stabilization energy ~ 23 Kcal/mole Kb = 2.3 X 10-9 3 2 N 1 6 5 4 N N CH3 -picoline docsity.com Pyridine important solvent & base (~ 3o amine) Reactions: 1) EAS (much less reactive than benzene ~ nitro) N KNO3, H2SO4, 370 o N NO2 3% yield H2SO4, SO3, HgSO4 220o, 24 hours N SO3 H Br2, 300 o N N Br Br Br + Friedel-Crafts no reaction docsity.com N N N Br Cl Br NH3, 200 o NH3, 200 o NH3, 200 o NR N NH2 N NH2 N N H Z Z H activated to nucl. arom. subts. directs alpha & gamma docsity.com Pyridine, reactions 3) As base Kb = 2.3 X 10-9 N N HBr CH3I N H Br N CH3 I 4o salt docsity.com Pyridine, reactions 4) reduction N H2, Pt HCl, 25o, 3 atm. N H piperidine Kb = 2 X 10-3 aliphatic 2o amine docsity.com HC H2C H2C OH OH OH H+ -H2O HC CH CH2 O acrolein NH2 + N H CH2 CH2 C O H H+ N H CH2 CH2 C OH H EAS N H H OH N H NO2 N NH2 + -H2O docsity.com Heterocycles as you would expect! O N H S angle strain O O O ethers NH N H N H amines docsity.com O N H S N EAS nucleophilic aromatic substitution docsity.com
