PYRROLE Occurs in coal tar. Colourless liquid with odour of chloroform, mp -24C, bp 131C, slightly soluble in water. It has resonance energy of 100KJ per mole. It is found in proline and nicotine.

RETROSYNTHESIS OF PYRROLE

Acid-base rxns of pyrrole Protonation occurs at C-2

Electrophilic substitution rxns

COMPOUNDS CONTAINING PYRROLE OR PYRR OLIDINE

IMIDAZOLE

RETROSYNTHESIS OF IMIDAZOLE

COMPOUNDS CONTAINING IMIDAZOLE

PYRAZOLE CONT’D

PYRAZOLE CONT’D

RETROSYNTHESIS OF OXAZOLE

OXAZOLE CONT’D

OXAZOLE CONT’D OXAZOLE IS COLOURLESS LIQ, SMELLS LIKE PYRIDINE, SOL, IN WATER, ARYL-SUBSTITUTED STRONGLY FLUORESCENT. SUITABLE AS LUMINOUS SUBSTANCES (LIQ SCINTILLATION COUNTERS OR USED AS BRIGHTENING AGENTS)

SUMMARY-RXNS

1,3-benzoxazole Colourless liq, sol. In water. Aroma constituent in cocoa, coconuts, walnuts and beer. Derivative occurs in fireflies.

Colourless crystals, moderately sol in water, very soluble in ethanol

BENZO[b]THIPHENE Benzo[b]thiophene occurs in coal tar and roasted coffee beans

Derivative used as antibacterial drug(with nitrophenyl side chain), colourless, oily liq, water insoluble, occurs in coal tar

Colourless, fluorescent crystals,occurs in coal tar

Electro subs occurs at C-3. Colourless solid leaflet crystals, mod Electro subs occurs at C-3. Colourless solid leaflet crystals, mod. Sol in water. Occurs in coal tar and jasmine oil

Bufotein-poison on frog skin; psilocin-causes hallucinations

NOMENCLATURE SIX MEMB.

PYRILIUM ION Planar and slightly distorted hexagon. It is aromatic. Positive charge at 2,4,6.Hence nucleophilic attack at 2,4,6

RING OPENING OH adds at pos 2 and with heating ring opens

Ring opens to form 1,5-diketone or 1,5-dialdehyde

RING OPENING CON’D Grignard reagent can also add at pos 2. Heating opens up the ring to form dienone

2H-PYRAN The parent compd has not yet been isolated. However, 2,2-disubstituted derivatives have been isolated

THERMAL RING OPENING OF 2H-PYRAN DERIVATIVE This compd undergoes thermal ring opening

2H-PYRAN-2-ONE Bp of 208C, colourless liq. It behaves like 1,3-dienes and also like lactones

RXN OF 2H-PYRAN-2-ONE

SYNTHESIS OF TETRAHYDROPYRAN Dehydration rxn catalyzed by acid. Loss of water with subsequent cyclization

2H-CHROMENE It is found in natural products like plants

2H-CHROMEN-2-ONE or coumarin Occurs in plants (lavender), mp 68C, colourless crystalline solid. Reacts like lactone.

LACTONE RING OPENING Ring opens to form free carboxylic acid

1-BENZOPYRILIUM ION The derivative of this compd is found in leaves and flowers. It gives various colours to leaves and flowers

BENZOPYRILIUM ION CONT’D Numerous red, blue and violet pigments of blossom and leaves are made of this derivative. Occurs as glycosides(anthocyanins)

4H-PYRAN Unlike 2H-Pyran, the parent compd is known. It is synthesized from 1,5-diketone or 1,5-dialdehyde

SYNTHESIS OF 4H-PYRAN

4H-PYRAN-4-ONE Mp 32C, colourless, crystalline. Occurs in the bark of larch tree; also formed by dry distillation of starch and cellulose. Also found in opium

4H-1-BENZOPYRAN(4H-CHROMENE) Derivatives found in plants

4H-CHROMEN-4-ONE(4H-1-BENZOPYRAN-4-ONE) Mp 59C, colourless needles. Also known as chromone. Derivative found in plants

OTHER DERIVATIVES OF 4H-CHROMEN-4-ONE Phenyl at pos 2 gives FLAVONES, eg apigenin, leteolin. Occurs in yellow pigments in plants

FLAVONES CONT’D Flavones have a wide spectrum of biological activity-anti-tumor, anti-inflammatory. Also used as dyes in textile industry

FLAVONES CONT’D Quercetin found in apples. Major constituent of red wine. Found to reduce incidences of cardiovascular diseases

Chroman, flavan, flavanol etc Constituent of vitamin E

Vitamin E

Flavan, flavanol

DIBENZOPYRAN DERIVATIVES