The analgesic naproxen can be prepared by a stepwise...

The analgesic naproxen can be prepared by a stepwise reaction sequence from ester $\textbf{A}$. Using enolate alkylation in one step, what reagents are needed to convert $\textbf{A}$ to naproxen? Write the structure of each intermediate. Explain why a racemic product is formed.

Key Concepts

Stereochemical Considerations and Racemization

During the enolate alkylation process, the intermediate enolate is planar, meaning that the electrophile can attack from either the top or bottom face of the enolate equally. This non?stereoselective addition leads to the formation of a racemic mixture when a new chiral center is created, as both enantiomers are produced in equal amounts.

Stepwise Reaction Sequence in Synthesis

The overall synthetic strategy typically involves sequential reactions in which the starting ester is first converted into its enolate form with a strong base, then alkylated with the appropriate electrophile, and finally, additional steps such as hydrolysis may be performed to furnish the target carboxylic acid. This sequence highlights the importance of reaction order and controlled conditions to achieve the desired product.

Enolate Formation

This concept involves generating an enolate ion by deprotonating the alpha carbon of a carbonyl compound, such as an ester, using a strong, non?nucleophilic base. The resulting enolate, which is stabilized by resonance between the oxygen and the adjacent carbon, serves as a nucleophile in subsequent carbon–carbon bond forming reactions.

Alkylation Reaction Mechanism

In the alkylation step, the nucleophilic enolate attacks an electrophilic carbon (commonly part of an alkyl halide), forming a new carbon–carbon bond. This reaction is a cornerstone of organic synthesis, allowing for the construction of more complex molecules through the addition of substituents at the alpha position of carbonyl compounds.

Transcript

0:00 Hello everyone.

00:01 Today we're doing chapter 23 problem 18.

00:03 This problem tells us that neproxin can be prepared from a using inolate alkylation in one step and ask us to convert a to naproxin and write all the reagents that are needed and the structure of each intermediate.

00:20 And explain why racemic product is formed.

00:22 So let's draw the structure of a again just so we can be very clear of how it looks.

00:39 So you have these two benzene rings in conjugation with one another.

00:47 And what we have here is now this ester that is being converted to a carbonylacly acid.

00:58 So this is a carboxylic acid here.

01:03 And we're also gaining one carbon.

01:06 So what we have is a carbonyl group, an alpha to that carbonyl group.

01:12 We have an alpha carbon.

01:14 And off as alpha carbon, we have alpha -carbon.

01:16 We know by alpha protons is that they're acidic, so using a strong base, we can easily rip those protons off and make this carbon into a very strong nucleophile in which we can add an alkaliid to add carbons to the alpha position.

01:31 And after, if you add acidic water, then we can hydrolyze this ester to form a carbacylacid acid.

01:36 So let's work through this.

01:38 So if i first step, i add lda and thf and very low temp, so minus 70 degrees.

01:47 Celsius.

01:50 The big bulky base being lda is going to rip off the is most acidic proton.

01:54 That's going to be this alpha proton here and we're going to form a carbanein.

02:11 Now this carbon ion is highly unstable so it's going to want to neutralize itself very badly.

02:17 So this is going to act as a very strong nucleophile.

02:19 It's very electron rich, very hard charge, negative charge, and it's going to attack any electrofile we add to it...

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