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CONCEPT: INTRO TO REDOX Oxidation reactions involve an increase in the content of a molecule Reduction reactions involve an increase in the content of a molecule EXAMPLE: Label the following transformations as oxidation or reduction. a. b. c. Page 2
CONCEPT: OXIDATION Oxidizing agents are used to oxidize molecules Most oxidizing agents add as much oxygen as possible while not breaking ANY C-C bonds. EXAMPLE: Which of the following compounds could be oxidized? These are called strong oxidizing agents. They include KMnO4 and the Cr 6+ reagents (H2Cr2O4, CrO3, K2Cr2O7, etc.) EXAMPLE: Draw the products of the previous molecules with a strong oxidizing agent PCC is a weak oxidizing agent. It reacts similar but can only add equivalent of oxygen to 1º alcohols. Page 3
CONCEPT: OXIDATION MECHANISMS One of the most popular oxidizing agents is the Jones Reagent. It can be generated through combination of a strong acid with a Cr6 + reagent. Mechanism: Page 4
PRACTICE: Predict the product of the following reactions a. b. c. Page 5
CONCEPT: REDUCTION Reducing agents are used to reduce molecules These reagents add hydrogens across π-bonds. Unsaturated hydrocarbons and carbonyls can be reduced. General Mechanism: Nucleophilic addition of hydrogen Reducing agents add to ALL π-bonds present. Multiple equivalents of hydrogen will react if possible. LiAlH4 is a strong reducing agent. It is able to reduce ANY carbonyl compound into alcohol EXAMPLE: Draw the products of the following molecules reacted with LiAlH4 NaBH4 is a weak reducing agent. It can only add equivalent of oxygen and can only reduce CHO and ketones EXAMPLE: Draw the products of the following molecules reacted with NaBH4 Page 6
CONCEPT: NUCLEOPHILIC ADDITION One of the most important ways that carbonyl compounds react is through nucleophilic addition. The carbonyl carbon is Nucleophilic Addition General Mechanism: Nucleophilic Addition General Reactions: Page 7
CONCEPT: PREPARATION OF ORGANOMETALLICS Organometallics are alkylating agents that have mostly group IA or group IIA metals bonded to a carbon structure They can also react as strong. Beware of cross-reactions with acidic hydrogens. 1. Sodium Alkynides 2. Grignard Reagents 3. Organolithium Reagents 4. Gilman Reagents Page 8
CONCEPT: REACTIONS OF ORGANOMETALLICS 1. Substitution/Elimination on Alkyl Halides 2. Nucleophilic Addition on Ketones and Aldehydes 3. Nucleophilic Acyl Substitution on Esters 4. Base-Catalyzed Epoxide Ring Opening Page 9
CONCEPT: USE OF PROTECTING GROUPS Organometallics are powerful bases. They will react with any acidic protons available, ruining the reagent. We can use tert-butyl or silyl ethers to protect alcohols from deprotonation by organometallic reagents p-toluenesulfonic acid is an acid commonly used for this step (abbrev. TsOH or ptsa) EXAMPLE: Provide the mechanism and final product for the following transformation Page 10
PRACTICE: Predict the product of the following reaction. Page 11
PRACTICE: Predict the product of the following reaction. Page 12
PRACTICE: Predict the product of the following reaction. Page 13
PRACTICE: Predict the product of the following reaction. Page 14
PRACTICE: Propose a synthesis to accomplish the following transformation. Page 15
PRACTICE: Propose a synthesis to accomplish the following transformation. Page 16
PRACTICE: Propose a synthesis to accomplish the following transformation (Hint: 4 steps) Page 17