Question

Show how to bring about each conversion using a lithium diorganocopper reagent. (a) (b)

Short answer

Question: Describe the general process for completing a conversion using a lithium diorganocopper reagent. Answer: The general process for completing a conversion using a lithium diorganocopper reagent involves four steps: 1) Formation of the lithium diorganocopper reagent through the reaction of an organolithium compound with a copper(I) halide salt; 2) Identification of the substrate and the reaction type, such as nucleophilic substitutions, conjugate additions, or carbon-carbon bond formations; 3) Performing the reaction with the organocopper species, which acts as a nucleophile and attacks the electrophilic carbon of the substrate; and 4) Determining the product of the reaction, which depends on the substrate and the type of reaction being performed.

Step-by-step solution

Formation of lithium diorganocopper reagent

To begin with, we need to form the lithium diorganocopper reagent. These reagents are typically formed by the reaction of an organolithium compound with a copper(I) halide salt, such as copper(I) iodide: R-Li + CuI → R-Cu-Li + LiI In this step, the organolithium species performs a nucleophilic attack on the copper(I) halide, displacing the halide and forming the organocopper species.

Identify the substrate and reaction type

Next, we must identify the substrate and determine the type of reaction we're performing with the lithium diorganocopper reagent. Depending on the specific situation, the organocopper reagent can be used in nucleophilic substitutions (e.g., the formation of ketones from acid chlorides), conjugate additions (e.g., reacting with α, β-unsaturated carbonyl compounds), or carbon-carbon bond formations (e.g., reacting with alkyl halides).

Perform the reaction with the lithium diorganocopper reagent

Once the reaction type has been determined, we can perform the reaction with the lithium diorganocopper reagent. In general, the organocopper species will act as a nucleophile, attacking the electrophilic carbon of the substrate. The exact mechanism will depend on the type of reaction being performed: - For nucleophilic substitutions, the organocopper nucleophile attacks the carbonyl carbon, displacing the leaving group (usually a halide or an ester) and forming a new carbon-carbon bond. - For conjugate additions, the organocopper nucleophile adds across the double bond of an α, β-unsaturated carbonyl compound, forming a new carbon-carbon bond and a new carbonyl compound. - For carbon-carbon bond formations, the organocopper nucleophile attacks an electrophilic carbon of an alkyl halide or vinylic system. This generates a new carbon-carbon bond.

Determine the product of the reaction

After completing the reaction, we must determine the product of the reaction. The product depends on the substrate and the type of reaction being performed: - In nucleophilic substitutions, the product will typically be a ketone or an ester (depending on the leaving group). - In conjugate additions, the product will be a new carbonyl compound with the organocopper species now attached at the β-position of the original substrate. - In carbon-carbon bond formations, the product will consist of two organic fragments connected by a new carbon-carbon bond. With these steps, you can now show how to perform each specific conversion using a lithium diorganocopper reagent.