19.9 Retrosynthesis with Aldehydes and Ketones | Organic Chemistry

Chad's Prep

6 Apr 202123:06

EducationalLearning

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TLDRThe video script discusses various organic chemistry synthesis problems, focusing on the transformation of aldehydes and ketones into different compounds. It reviews synthesis reactions, reactions of aldehydes and ketones, and approaches to retrosynthesis. The instructor emphasizes common methods for forming carbon-carbon bonds, such as aldol addition and Grignard reagent addition, and explores different synthetic pathways to achieve the desired products. The script also covers the synthesis of ketones from internal alkynes, the oxidation of secondary alcohols to ketones, and the use of the Wittig reaction to form alkenes. It concludes with a discussion on the importance of considering multiple synthesis pathways and the impact of reaction conditions on product yields. The instructor encourages students to practice more problems on their own and provides a resource for further study.

Takeaways

🔬 **Retrosynthesis Approach**: The process involves working backwards from the target molecule to identify possible precursors and synthetic routes.
⏪ **Carbon-Carbon Bond Formation**: Key methods for creating larger carbon chains include aldol addition and Grignard reagent addition.
🍂 **Aldehyde and Ketone Synthesis**: Reviewing synthesis reactions for aldehydes and ketones is crucial for understanding retrosynthetic pathways.
🔄 **Reactions of Aldehydes and Ketones**: Various reactions, such as oxidation and Grignard addition, are pivotal in forming the desired products.
📚 **Study Materials**: The speaker provides a weekly organic chemistry playlist and encourages subscription for updates.
⚖️ **Yield Considerations**: In retrosynthesis, the yield of each step is important, as low yields can affect the overall synthetic efficiency.
🔋 **Oxidation States**: The conversion between alcohols and aldehydes/ketones is a common theme, with the choice of oxidizing agent depending on the alcohol's substitution.
🔁 **Elimination Reactions**: These reactions can be used to form alkenes but must be carefully chosen to ensure the correct product is formed.
🧪 **Wittig Reaction**: A powerful method for converting carbonyl groups into alkenes, which can be useful in certain synthetic pathways.
🔬 **Reagent Selection**: The choice of reagents is critical, as some can lead to more straightforward or efficient syntheses than others.
⛓ **Reaction Mechanisms**: Understanding the mechanisms of reactions like Grignard reagent formation and electrophilic aromatic substitution is key to successful retrosynthesis.

Q & A

What is the main focus of the video script?
-The video script focuses on teaching organic chemistry, specifically the synthesis and retrosynthesis of aldehydes and ketones, and how to approach various synthesis problems.
What are the two most prominent ways to form a carbon-carbon bond in the context of the script?
-The two most prominent ways to form a carbon-carbon bond mentioned in the script are through aldol addition and Grignard addition.
What is the significance of the Markovnikov's rule in the context of the script?
-Markovnikov's rule is significant in the script as it predicts the position of the hydroxyl group in the hydration of alkenes, which is crucial when forming alcohols that can be further oxidized to ketones.
Why is PCC (Pyridinium Chlorochromate) often used to oxidize secondary alcohols to ketones in the script?
-PCC is used because it is a weaker oxidizing agent suitable for oxidizing secondary alcohols to ketones without over-oxidizing them to carboxylic acids.
What is the Wittig reaction mentioned in the script, and how is it used in synthesis?
-The Wittig reaction is a chemical reaction that involves the conversion of a carbonyl compound (aldehyde or ketone) into an alkene using a phosphorane, typically a phosphonium ylide. In the script, it is suggested as a method to form alkenes, which can be further converted into other functional groups.
How does the script suggest forming an alkene from an alcohol?
-The script suggests forming an alkene from an alcohol through elimination reactions, specifically using concentrated H2SO4 to shift the equilibrium towards the alkene.
What is the role of Grignard reagents in the synthesis problems discussed in the script?
-Grignard reagents play a crucial role in forming new carbon-carbon bonds by reacting with carbonyl compounds like ketones and aldehydes, leading to the formation of alcohols, which can be further manipulated in the synthesis process.
Why is the formation of an alkyne not a preferred method in the retrosynthesis problems presented in the script?
-The formation of an alkyne is not preferred because it often leads to lower yields due to the possibility of forming carbonyl groups in undesired positions, and it may also involve more steps to achieve the desired product.
What is the importance of considering the number of steps in a synthesis when solving retrosynthesis problems?
-The number of steps in a synthesis is important because each step may require purification and can lead to product loss, thus affecting the overall yield. Generally, fewer steps are preferred for higher efficiency and yield.
How does the script approach the synthesis of esters?
-The script approaches the synthesis of esters by first considering the formation of a ketone, which can then be converted into an ester using the Baeyer-Villiger oxidation, specifically with a peroxy acid like mCPBA (meta-chloroperoxybenzoic acid).
What is the significance of the E2 elimination reaction in the script's discussion on synthesis?
-The E2 elimination reaction is significant as it is a method to form alkenes from alkyl halides, which can then be used in further reactions to synthesize the target molecules, such as alcohols and ketones.

Outlines

00:00

🔍 Retrosynthesis of Carbon Chains with Aldehydes and Ketones

This paragraph discusses the process of retrosynthesis, focusing on the creation of carbon-carbon bonds to extend carbon chains, specifically turning a four-carbon alcohol into a seven-carbon ketone. The speaker reviews synthesis reactions and strategies, such as satellite addition and Grignard addition, to achieve the desired product. The paragraph also explores the limitations of using internal alkynes and the preference for using secondary alcohol oxidation with PCC (Pyridinium Chlorochromate) for better yield and control over the synthesis process.

05:01

🧪 Synthesis Strategies Involving Wittig Reaction and Elimination

The second paragraph explores the synthesis of an alkene from cyclohexene, considering both Wittig reaction and elimination reactions as potential pathways. The speaker discusses the challenges of creating specific alkyl halides and the use of strong bases like sodium ethoxide for elimination reactions. The Wittig reaction is also considered, where a phosphorane (phospholide) reacts with a ketone to form a double bond. The paragraph concludes with the synthesis of the desired product through a three-step process involving the Wittig reaction and the preparation of the necessary reagents.

10:02

📜 Multi-Step Syntheses and the Importance of Efficiency

This paragraph delves into the synthesis of an alcohol from benzene, emphasizing the need for a carbon-carbon bond formation via Grignard addition. The speaker outlines the steps to create a Grignard reagent from an alkyl halide and subsequent reactions to form the desired alcohol. The paragraph also touches on the conversion of benzene to an aryl bromide using electrophilic aromatic substitution. The synthesis is presented in a three-step process, highlighting the importance of minimizing steps to maintain high yields and efficiency in the synthesis process.

15:02

⚖️ Balancing Synthesis Pathways for Carbon Chains and Functional Groups

The fourth paragraph addresses the synthesis of a seven-carbon alkyl halide with an amine functional group. The speaker explains the formation of amines through the addition of a primary amine to a ketone or aldehyde, leading to the creation of a carbon-oxygen double bond. The paragraph outlines the synthesis of an aldehyde from an alcohol using PCC as the oxidizing agent and the importance of creating the alcohol at a specific location through hydroboration-oxidation. The synthesis strategy involves E2 elimination using potassium tert-butoxide as the base, resulting in a four-step process.

20:05

🔬 Ester Synthesis via Villiger Oxidation and Alternative Pathways

The final paragraph presented discusses the transformation of an alkene into an ester, maintaining the same number of carbons but altering the backbone to include an oxygen atom. The speaker focuses on the use of Baeyer-Villiger oxidation to convert a ketone into an ester, which necessitates the prior synthesis of the ketone. The paragraph explores alternative methods for ketone synthesis, including the hydration of terminal alkynes and the oxidation of secondary alcohols. Two viable synthesis pathways are presented: a four-step process involving alkyne hydration and a three-step process involving the oxidation of an alcohol, with the latter being potentially preferred for its efficiency.

Mindmap

Keywords

💡Retrosynthesis

Retrosynthesis is a method used in organic chemistry to work backward from a target molecule to simpler precursors. It's a strategic process that helps chemists determine the necessary steps to synthesize complex molecules. In the video, the concept is central to solving the various synthesis problems presented.

💡Aldehydes

Aldehydes are organic compounds containing a carbonyl group bonded to at least one hydrogen atom. They are important in organic synthesis and are discussed in the video as starting materials that can be converted into other functional groups like ketones or alcohols.

💡Ketones

Ketones are carbonyl compounds where the carbonyl group is bonded to two other carbon atoms. They are key intermediates in organic synthesis and are discussed in the video in the context of their synthesis from alcohols and their role in forming larger carbon chains.

💡Carbon-Carbon Bond Formation

The formation of carbon-carbon bonds is a fundamental reaction in organic chemistry, allowing for the creation of more complex molecules from simpler ones. In the video, various methods such as Grignard addition and aldol condensation are discussed for forming these bonds.

💡Grignard Reagent

A Grignard reagent is an organomagnesium compound used in organic synthesis to form new carbon-carbon bonds. In the video, it is mentioned as a key reagent for converting alcohols into ketones and for adding carbon groups to aldehydes or ketones.

💡Oxidation

Oxidation in organic chemistry refers to reactions where a molecule loses electrons, often involving the addition of oxygen or removal of hydrogen. The video discusses the oxidation of primary and secondary alcohols to form aldehydes and ketones, respectively.

💡Elimination Reaction

An elimination reaction is a type of organic reaction where one or more atoms or groups are removed from a molecule, often resulting in the formation of a double bond. In the video, elimination reactions are considered as a method to form alkenes from alcohols.

💡Wittig Reaction

The Wittig reaction is an organic reaction that involves the conversion of a ketone or aldehyde to an alkene using a phosphorane, typically a phosphonium ylide. The video discusses the potential use of the Wittig reaction to form alkenes in the synthesis problems.

💡Alkyne

An alkyne is a hydrocarbon containing at least one carbon-carbon triple bond. In the video, alkynes are considered as intermediates that can be hydrated to form ketones, although the presenter notes potential issues with the Markovnikov rule and yield.

💡Aldol Condensation

Aldol condensation is a chemical reaction that involves the formation of a new carbon-carbon bond between the alpha carbon of an enolate ion and a carbonyl group. It is mentioned in the video as a possible method for forming larger carbon chains from smaller carbonyl compounds.

💡Acetylide

An acetylide is a compound containing the acetylide ion, which has a carbon triple bond with a metal. In the video, it is mentioned in the context of using metal acetylides to form carbon-carbon bonds, although the presenter concludes that it would not be the most efficient method for the given synthesis problems.

Highlights

Review of synthesis reactions for aldehydes and ketones

Introduction to retrosynthesis problems involving aldehydes and ketones

Discussion on creating larger carbon chains through carbon-carbon bond formation

Emphasis on the two prominent methods for carbon-carbon bond formation: aldol addition and Grignard addition

Exploration of the limitations of using internal alkynes for carbonyl group placement

Explanation of converting secondary alcohols to ketones using PCC or chromic acid

Strategy for identifying the appropriate Grignard reagent and its corresponding alcohol

Technique for synthesizing aldehydes from primary alkyl groups using weaker oxidizing agents

Consideration of multiple synthesis pathways and their respective yields

Analysis of the Wittig reaction as a method for creating alkenes from ketones and aldehydes

Evaluation of the feasibility of forming alkyl halides from specific carbon chain structures

Discussion on the synthesis of alcohols through Grignard addition and subsequent workup steps

Identification of the most straightforward and efficient synthesis routes based on step count and yield

Use of E2 elimination and bulky bases for specific alkene formation

Synthesis of esters through the Baeyer-Villiger oxidation of ketones

Differentiation between primary, secondary, and tertiary alcohols in the context of oxidation reactions

Utilization of hydroboration-oxidation for the selective formation of alcohols at specific carbon positions

Importance of considering the number of steps and overall yield when evaluating the efficiency of a synthesis

Advice on practicing retrosynthesis problems to build a repertoire of reactions and strategies

Transcripts

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Related Tags

Retrosynthesis Aldehydes Ketones Organic Chemistry Synthesis Pathways Chemical Reactions Alkene Hydration Wittig Reaction Grignard Reagent Acetylide Formation Ozonolysis Elimination Reaction Alcohol Oxidation Benzene Substitution Amine Formation E2 Elimination Vicinal Dihalide Villiger Oxidation