Reduction of the benzylic carbon Benzyl ethers as protecting agents Phenols Nucleophilic aromatic substitution would go by addition elimination mechanism idea Nucleophilic aromatic substitution benzyne elimination addition Example benzyne Arene diazonium ions Reactions of aryl amines and diazonium ions Synthesis example with diazonium ions Diazonium ions as electrophiles in EAS reactions Reactions of Phenols 1 Acidic cleavage of aryl ethers mechanism 2 Formation of Ethers mechanism phenol is a strong activator sometimes can observe multiple additions of electrophile 3 Phenols as Nucleophile in EAS 4 Base mediated Substitution mechanism 3 3 sigma tropic rearrangement Electrocyclic Reactions Claisen rearrangement Cope Rearrangement Claisen Rearrangement Examples Chair like transition state Benzoquinones 22 8 1 Radical oxidation of phenols 2 Reactions Biological Reactions 22 9 certain vitamins can stabilize free radicals all has to do with resonance stability Chapter 25 I Naming Heterocycles 25 1 1 Systematically named as heterocycloalkanes aza N oxa O thia S phospha P 2 Common names pg 1168 II Reactivity of nonaromatic heterocycles 25 2 1 3 4 membered rings ring opening relief of ring strain drives this rxn by carbocation TS see 9 9 2 5 membered rings unreactive towards nucleophiles bases solvents III Structure and properties of 5 Membered Aromatic Heterocycles 25 3 1 Aromaticity and electron count A Mete electronnegative atoms are less aromatic S N O B Other heteroatoms do not contribute to the resonance 2 General synthesis Paal Knorr IV Reactions of 5 membered Aromatics 25 4 1 EAS analogs A C2 Substitution electron rich so you do not need a catalyst B Mechanism stability makes three resonance structures more stable makes two resonance structures C Reaction rate benzene S O N D Indole will attack at C3 2 Acidity and Basicity A Pyrrole is a weak base H on C B Pyrrole is a good acid hybridization delocalization of anion 3 Other reactions A H cat Hydrolysis of furans B Desulfurization of thiopene C Diels Alder Reaction of furan 14 8 furan is least aromatic O is most electronegative V Structure and Synthesis of Pyridine 25 5 1 Aromaticity lone pairs are NOT part of the pi system 2 Named as azabenzenes 3 Synthesis the Hantzch Pyridine Synthesis condensation of ammonia an aldehyde 2 beta dicarbonyls VI Reactions of Pyridines 25 6 1 Pyridine is electron poor EAS are slow and di cult and occur at C3 addition of electron donating groups makes it a better electrophile A C3 intermediate will NOT put on N 2 Pyridines undergo easy NArS A At C2 and C4 puts on N Chichibabin mechanism B With alkyl anions C Good LGs make for faster reactions must be at C2 or C4 position VII Quinolines and Isoquinolines 25 7 1 Named as azanaphthalenes 2 EAS reactions occur on benzene portion attack at 5 and 8 due to stability of intermediates see end of chapter 16 for review 2 NArS work well VIII Alkaloids 25 8
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