The Reformatsky reaction is an addition reaction in which an...

Key Concepts

?-Halo Esters

?-Halo esters are critical starting materials in the Reformatsky reaction. They contain a halogen atom bonded to the carbon adjacent to the carbonyl group, which, upon treatment with zinc, facilitates the formation of the organozinc reagent. This substrate design is essential for the generation of the nucleophilic species required for the subsequent addition to carbonyl compounds.

Nucleophilic Addition to Carbonyl Compounds

In the context of the Reformatsky reaction, the organozinc intermediate acts as a nucleophile that attacks the electrophilic carbon of the carbonyl group in aldehydes or ketones. This nucleophilic addition results in the formation of a new carbon–carbon bond and, upon subsequent workup, leads to a ?-hydroxy ester. This mechanism is a classical example of nucleophilic addition involving organometallic reagents.

Organozinc Reagents

Organozinc reagents are formed in situ by the reaction of an ?-halo ester with zinc metal. They are less reactive than Grignard reagents, which is a key feature in controlling the chemoselectivity of the reaction, enabling the addition specifically to the carbonyl group while preserving the ester functionality present in the same molecule.

Reformatsky Reaction

The Reformatsky reaction is a carbon–carbon bond forming reaction where an ?-halo ester reacts with zinc to form an organozinc intermediate that then adds to a carbonyl compound, such as an aldehyde or ketone, forming a ?-hydroxy ester. This reaction leverages the moderated reactivity of the organozinc species, which allows for selective addition to the carbonyl group without unwanted reactions at the ester moiety.

Transcript

00:01 Okay, this problem deals with the reformatky reaction in which we have a zinc bromide attached to this alpha carbon, and then the alpha carbon is going to behave as a nucleophile to attack either an aldehyde or a ketone or a ketone or a ketone or a ketone or a ketone or a ketone or a bit.

00:12 It can attack virtually any carbonyl.

00:15 But with zinc bromide, it's going to make this carbonyl, or specifically this alpha chlorides, it's going to make this carbonyl, or specifically this alpha -chlorids, esters, ketones, alvehydes, it can attack virtually any carbonyl.

00:26 But with zinc bromide, it's going to make this carbonyl, or specifically this alpha carbon, less reactive.

00:32 It's going to make it less nucleophilic.

00:33 So this is not going to perform a self -closin connoissation, for example.

00:37 Okay, and that is simply because this carbon is not as nucleophilic as it would be to have a self -closin connoissellation.

00:44 Okay, so with that in mind, let's go ahead and proceed with these reactions in terms of breaking them down.

00:48 So for this one, i have my ester, and then i have this connection to my alcohol.

00:54 Okay, so with reformatucky reactions, we have to start off with my ester.

00:59 So i'm going to have my och3 on this side and then my carbonyl on this side.

01:02 So that is what i'm going to start off with.

01:04 Okay, but the question is, what am i going to be attached to? so as i know, attached to the alpha carbon, i'm going to have the connection to my zinc bromide.

01:11 Okay, the zinc bromide allows my carbon, my alpha carbon to be nucleophilic.

01:14 Okay, that nucleophilic carbon can attack virtually a, well, at least a reactive ketone or alvehyde.

01:21 So it's going to either attack a ketone or an alvehyde in this case.

01:23 And in this case, we have the connection to one, two, three, four carbons attached to this alpha carbon.

01:29 So that's four carbons, meaning that i'm going to have a one, two, three, four carbon compound, and that is going to be an aldehyde.

01:36 Okay, so basically this carbon nucleophile attacks this carbonyl, moving the electrons up to the oxygen, and then that oxygen is going to have a negative charge, but it's eventually going to get protonated by water in this solution.

01:47 Okay, so those are the components of this reaction.

01:50 Okay, what about this one? so this one, as we can see, we have a carboxylic acid.

01:55 Okay, with reformatomy reactions, we have to have an ester.

01:58 Okay, and that is depicted in the first reaction and the example given above.

02:02 Okay, so we have to have that carboxylic acid originate as an ester.

02:07 Okay, so i'm just going to transform this into, let's just say, anethoxide attached to that carbonyl.

02:12 And then again, we're going to have the carbon.

02:14 That alpha carbon is going to be connected to zinc bromide.

02:17 So zinc bromide.

02:18 Okay, in addition to that zinc bromide, we're also going to have the connection to my ch2, ch3.

02:23 And we also have a connection to these three carbons over here, but these three carbons are connected to my alcohol.

02:28 So i don't have to worry about that yet in terms of this singular molecule.

02:32 Okay, so again, we have the connection to my ch2, ch3 in addition to that zinc bromide on that alpha carbon.

02:38 Okay, so that is that molecule, and we're going to rack that with a one, two, three carbon compound in which i have an albehyde.

02:44 So one, two, three carbons, aldehyde.

02:47 Okay, this nuclear fluid carbon can go ahead and attack that carbonyl, moving the electrons up to the, the oxygen, which is going to make an oxygen with a negative charge, but that is eventually going to get protonated by water.

02:57 Okay, and that is going to form almost my compound, but again, we want to hydrolyze that ester into forming my carboxic acid.

03:04 So it's going to undergo this reaction right here between these two compounds, and then it's going to react with acid water and heat in order to form my desired compound.

03:13 Okay, next step, we have this one.

03:14 So this one is going to be a little bit different than the ones that we've previously analyzed in the fact that i have my carbocosok acid, and i also have this alpha beta unsaturated system.

03:23 So that is characterized by the presence of my alken between my alpha and beta carbon...

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