③ [Lindlar catalyst](https://jb243.github.io/pages/1363#:~:text=syn%20%EC%B2%A8%EA%B0%80%20%EB%B0%98%EC%9D%91%20%3A-,Lindlar,-%EC%B4%89%EB%A7%A4%20(P%2D2)

○ Catalyst consisting of Pd, CaCO₃ (or BaSO₄), lead (Ⅱ) acetate ((CH₃COO^-)₂Pb²⁺), quinoline, etc.

④ LiAlH₄ and NaBH₄

○ LiAlH₄ (LAH): Strong reducing agent

○ Carboxylic acids → Primary alcohols

○ Aldehydes → Primary alcohols

○ Ketones → Secondary alcohols

○ Consider steric hindrance in reduction reactions

○ NaBH₄: Weak reducing agent

○ Carboxylic acids → No reaction

○ Aldehydes → Primary alcohols

○ Ketones → Secondary alcohols

○ Why LiAlH₄ is stronger than NaBH₄

○ Reason 1: Unlike B, Al is in the 3^rd period, making it easier for hydrogen to leave

○ Reason 2: Al has lower electronegativity, resulting in a larger δ^- for H

○ LiAlH₄ reacts vigorously with H₂O, so simultaneous addition of H₂O should be avoided: LAH is mainly used with THF solvent

⑤ Na₂SO₃

2. Organometallic Reagents

⑴ Overview

① Organometallic reagents perform carbon-carbon coupling reactions

② Metal ions in compounds carry δ⁺ charge, alkyl groups carry δ^- charge

⑵ Grignard Reagents: RMgX

① Preparation: RX + Mg (catalyst: anhydrous ether) → RMgX

② Reaction: In RMgX, Mg becomes δ⁺ leading to strong negative charge on R, which connects to electrophilic carbons

Figure 1. Example of Grignard reagent reaction with an ester

○ Carbonyl group (C=O): reacts

Figure 2. Organometallic reagent reaction of aldehyde

Figure 3. Organometallic reagent reaction of ketone

○ Acyl chloride, acid anhydride, ester: reacts

○ Phosgene (phosgen), carbonate ester: reacts

○ Carboxylic acid: does not react

Figure 4. Grignard reagent and carboxylic acids

③ Grignard reagents react with carbons that have low steric hindrance

④ Limitation in Organic Halides

○ Organic bromides and organic iodides: Grignard reagents are easily formed

○ Organic fluorides: Grignard reagents are hardly formed

④ Alcohol Protection Reactions (e.g., tosylation, mesylation)

○ If an acidic hydrogen is present in RX, Mg acts as a Lewis base and reacts with the hydrogen. For example, alcohols do such behavior.

○ Thus, alcohols are protected from Mg via alcohol protection reactions

⑶ Alkyl Lithium Reagents: RLi

① Preparation

② Reaction: In RLi, Li becomes δ⁺ leading to strong negative charge on R, which connects to electrophilic carbons

○ Alkyl lithium reagents can react with carboxylic acids unlike Grignard reagents and Gilman reagents

⑷ Gilman Reagents: R₂CuLi

① Preparation: 2RLi + CuI (catalyst: anhydrous ether) → R₂CuLi

② Reaction: In R₂CuLi, CuLi becomes δ⁺ leading to strong negative charge on R. Connect a single R to an electrophilic carbon.

○ 1-1. Reaction of primary alkyl halides with S_N2 mechanism

○ 1-2. Halogen substitution reactions of alkenes: Stereoconfiguration Z, E is preserved

○ Gilman reagents are unreactive with carbonyl groups (C=O)

○ Exception 1. Formation of ketones from acyl chlorides: Acyl chlorides are reactive, with the R group attaching to the ketone carbon and the -Cl group releasing

○ Exception 2. Enone and 1,4-addition reaction (Michael addition): In the case of β-halo carbonyl E1cB, a carbon-carbon coupling reaction occurs at an alkene position remote from the ketone

Figure 5. Reaction of Gilman reagent

Input: 2019.03.10 19:38

1401

Chapter 20. Redox and Organometallic

1. Oxidation-Reduction Reactions

2. Organometallic Reagents

results matching ""

No results matching ""