Devise a synthesis of each alkene using a Wittig reaction to form the double bond. You may use b

Devise a synthesis of each alkene using a Wittig reaction to...

Key Concepts

Retrosynthetic Analysis

Retrosynthetic analysis is a strategy used in organic synthesis to break down complex target molecules into simpler precursors. By working backwards from the final product, chemists can identify suitable starting materials and design reaction sequences, including the Wittig reaction, that assemble the desired molecular structure efficiently.

Carbonyl Compound Synthesis

Successful implementation of the Wittig reaction depends on the availability of carbonyl compounds. These are usually prepared from simpler starting materials such as alcohols or aromatic compounds, often through oxidation reactions. This conversion is essential to generate the electrophilic partner needed for the olefination reaction.

Use of Simple Starting Materials in Synthesis

Designing synthetic routes using readily available small molecules, like benzene and organic alcohols, emphasizes the practical application of fundamental organic transformations. This approach underlines the importance of converting simple precursors through well-established reactions into more complex structures in a stepwise and efficient manner.

Wittig Reaction

The Wittig reaction is a method used to form carbon–carbon double bonds by reacting a phosphonium ylide with a carbonyl compound. It is significant in organic synthesis for constructing alkenes with controlled stereochemistry and is often chosen when a precise introduction of a double bond is required.

Phosphonium Ylide Formation

Phosphonium ylides are key intermediates in the Wittig reaction, typically formed by treating a phosphonium salt with a strong base. The process involves converting an alkyl halide into a phosphonium salt via reaction with triphenylphosphine, followed by deprotonation to yield the ylide that acts as a nucleophile towards carbonyl compounds.

Transcript

00:03 This is the answer to chapter 21, problem number 62 from the smith organic chemistry textbook.

00:11 And this problem asks us to construct three molecules, and we're given some constraints around their construction.

00:22 So each of the molecules were asked to construct as an alken.

00:26 We're told that the alkenes itself needs to be constructed by using a vidig reaction.

00:34 And we're also told we can only use benzene and organic alcohols having four or fewer carbons as our starting materials.

00:45 So basically we're going to have to make everything that we need from butanol or less and benzene.

00:55 So for a, we can, okay, well, so since we're told that we need to use a vidig to construct the alken in each instance, we should know that we're going to have to make the vitigry agent, and we're going to have to make the carbonyl compound that the vidig is going to react with.

01:21 So for each of these, we're going to essentially just make two pieces and then connect those two pieces at the alkeen via a vidig.

01:32 Pardon me, a vidig.

01:35 And so what we're trying to make for a looks like this.

01:55 And so we're going to disconnect at this double bond.

02:01 And so then we need to make the pieces to the left and to the right of the double bond.

02:08 And so we have four carbons to the left of the double bond.

02:15 One, two, three, four.

02:17 So we can start with butanol to make that portion, the left portion.

02:23 And we can, so you can really do this several different ways.

02:28 So what i'm going to do is i'm going to make the left part, my car, carbonyl part.

02:33 So we'll take butanol, we'll oxidize it up with pcc, and that's going to give us this aldehyde here.

02:44 And then, so obviously, our right part needs to be made into the vidig.

02:49 So there's two carbons over there, so we'll start with ethanol.

02:55 And then remember, the way that the book promotes making vidig is reaction of an alkaliad with trifectives.

03:03 Phenophosphine, followed by treatment with butyl lithium.

03:08 And so we need to get ethanol here to the alkaliad and then do that sequence.

03:14 And so pbr3 will replace our alcohol with a bromine.

03:22 And so after treatment with pbr3, we're there.

03:26 And then, as i said, we can do the vidig series to form a vidig.

03:35 We can actually save some space and just draw these as a single two -step process.

03:41 So trifanophosphine and then putilithium will get us to our vidig here.

03:50 Yeah, it's probably better to visualize it like this.

03:54 Ph 3p double bound to a ch, ch3.

04:03 And so there's our vidig.

04:07 And then we can combine the vidig that we just made with the aldehyde that we made above.

04:21 So there's our aldehyde.

04:25 And that is going to get us to our final product.

04:40 And of course we would get a mixture of e and z at this double bond.

04:46 But the problem also doesn't specify whether we want, or the other.

04:51 So this is fine.

04:54 Right.

04:55 So there's our product.

04:56 And so that's the answered part a.

04:58 So then b and c are going to follow exactly the same format where we can just deconstruct these molecules, essentially cut them across the double bond, and then make a carbonyl from one side and vidig from the other side and then just do the vidig reaction...

Please give Ace some feedback