Some of the most useful compounds for organic synthesis are...

Some of the most useful compounds for organic synthesis are Grignard reagents (general formula $\mathrm{R}-\mathrm{MgX},$ where $\mathrm{X}$ is a halogen), which are made by combining an alkyl halide, $\mathrm{R}-\mathrm{X}$ , halogen), which are made by combining an alkyl halide, R-X, with Mg. They are used to change the carbon skeleton of a starting carbonyl compound in a reaction similar to that with R-Li: (a) What is the product, after a final step with water, of the reaction between ethanal and the Grignard reagent of bromobenzene? (b) What is the product, after a final step with water, of the reaction between 2-butanone and the Grignard reagent of 2-bromopropane? (c) There are often two (or more) combinations of Grignard reagent and carbonyl compound that will give the same product. Choose another pair of reactants to give the product in (a). (d) What carbonyl compound must react with a Grignard reagent to yield a product with the ±OH group at the end of the carbon chain? (e) What Grignard reagent and carbonyl compound would you use to prepare 2-methyl-2-butanol?

Some of the most useful compounds for organic synthesis are Grignard reagents (general formula $\mathrm{R}-\mathrm{MgX},$ where $\mathrm{X}$ is a halogen), which are made by combining an alkyl halide, $\mathrm{R}-\mathrm{X}$ , halogen), which are made by combining an alkyl halide, R-X,
with Mg. They are used to change the carbon skeleton of a starting carbonyl compound in a reaction similar to that with R-Li:
(a) What is the product, after a final step with water, of the reaction between ethanal and the Grignard reagent of bromobenzene?
(b) What is the product, after a final step with water, of the reaction between 2-butanone and the Grignard reagent of 2-bromopropane?
(c) There are often two (or more) combinations of Grignard reagent and carbonyl compound that will give the same product. Choose another pair of reactants to give the product in (a).
(d) What carbonyl compound must react with a Grignard reagent to yield a product with the ±OH group at the end of the carbon chain? (e) What Grignard reagent and carbonyl compound would you use to prepare 2-methyl-2-butanol?

Key Concepts

Grignard Reagents

Grignard reagents are organomagnesium compounds typically represented by R–MgX, where R is an organic group and X is a halogen. They are crucial in organic synthesis because their carbon-magnesium bond is highly polar, making the carbon atom strongly nucleophilic. This allows them to attack electrophilic sites, particularly carbonyl groups, to form new carbon–carbon bonds.

Carbonyl Compound Reactivity

Carbonyl compounds, including aldehydes and ketones, feature a polarized carbon–oxygen double bond that renders the carbon atom electrophilic and susceptible to nucleophilic attack. Their reactivity is fundamental in various synthesis strategies where the addition of nucleophilic reagents leads to the formation of alcohols and other functionalized molecules.

Nucleophilic Addition Mechanism

The reaction of a Grignard reagent with a carbonyl compound follows a nucleophilic addition mechanism. In this process, the nucleophilic carbon of the Grignard reagent attacks the electrophilic carbonyl carbon to form an alkoxide intermediate. Subsequent protonation of this intermediate during the aqueous workup step yields the corresponding alcohol, thereby converting the carbonyl group into an alcohol function.

Synthetic Strategy and Reaction Design

Synthetic planning with Grignard reactions involves selecting appropriate Grignard reagents and carbonyl substrates to achieve the desired carbon framework and functional group placement in the target molecule. This strategic choice allows chemists to design alternative synthetic routes to the same product by varying the starting materials, and to control the formation of primary, secondary, or tertiary alcohols depending on the substitution patterns of the carbonyl compounds and the Grignard reagent.

Transcript

00:01 All right, so in this question, we're talking about greenered reagents and their reactivities.

00:05 So starting with a, we're asking what is the reaction after the final step with water between ethanol and a greenered reagent of bromobenzene.

00:17 So in other words, we have these two things reacting.

00:22 All right.

00:23 Let's say we have this bromobenzine.

00:33 All right.

00:33 And now the second step is we're going to add water.

00:36 So i'm just going to write 2h2o.

00:37 On here.

00:38 All right, so what the final product is going to be is essentially we're just going to have a benzene group off the carboxylic acids.

00:47 We're going to have something that looks like this.

00:55 Except instead of a carboxyl, we just have an oh -h.

01:01 All right, so for part b, we're asked a pretty similar question, except b is a reaction of two butanone and the greenerine reagent of two bromopropine.

01:15 So for b, starting with the two butanone, pretty simply just looks like this.

01:21 Next, we're adding this reagent.

01:29 And what that's going to do is lead to the formation of this product, right, where i have my oh here and then my propane off the edge there.

01:43 Right, moving on to c, this is asking, or i'm sorry, this is basically saying that oftentimes you can use.

01:51 Different methods to do these things and we're asked to propose a different method for producing the same product as a.

01:59 So again, there are a lot of ways you can do this.

02:01 The one that made sense to me immediately to produce the same product is just use benzaldehyde as our starting material and then add the kind of a methyl granary.

02:18 Right.

02:19 And that should produce the same thing after treatment of water where i just have...

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