Can the Beta carbons of ketones act as nucleophiles? And one more question.

[FROGGBUSTER]

I'm wondering what the mechanism would be of the reaction in the pic I've attached. It does seem the Beta carbon acts as a nucleophile and attacks the carboxylic acid.

I have a couple of questions, one general (#1) and one specific to the reaction shown (#2).

1. Does the Beta carbon of alpha-beta unsaturated ketones usually act as nucleophiles? I don't remember seeing any of these types of reactions in my undergrad course. Usually, a nucleophile is attacking the Beta carbon in an addition reaction.

2. Even in the presence of a catalyst, I don't know why this reaction can happen. The benzene ring is strongly de-activated is it not? It has a very electron-withdrawing group attached to it. Could it be because the compound is so extensively conjugated that the cation intermediate that forms (+ charge on the alpha carbon) is still relatively stable?


Thanks!

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[biophilia]

I'm wondering what the mechanism would be of the reaction in the pic I've attached. It does seem the Beta carbon acts as a nucleophile and attacks the carboxylic acid.

I have a couple of questions, one general (#1) and one specific to the reaction shown (#2).

1. Does the Beta carbon of alpha-beta unsaturated ketones usually act as nucleophiles? I don't remember seeing any of these types of reactions in my undergrad course. Usually, a nucleophile is attacking the Beta carbon in an addition reaction.

2. Even in the presence of a catalyst, I don't know why this reaction can happen. The benzene ring is strongly de-activated is it not? It has a very electron-withdrawing group attached to it. Could it be because the compound is so extensively conjugated that the cation intermediate that forms (+ charge on the alpha carbon) is still relatively stable?


Thanks!

Hmmm...this problem seems weird if you are only using H2SO4.

If you were allowed to pick the reagents (like in a synthesis problem). then I would do 1. SOCl2 (to turn the carboxylic acid into an acyl chloride) followed by 2.) AlCl3 (to do an electrophilic aromatic substitution reaction to close the ring).

If you only have H2SO4, maybe you could protonate the carbonyl oxygen to make the carbonyl carbon feel more electrophilic, then have a pi bond from the benzene ring attack the carbonyl carbon of the protonated carboxylic acid, but I don't think the carbonyl carbon is a good enough electrophile to make this a reasonable mechanism.

I don't know. I am curious to see what the proposed mechanism is.

 

[biophilia]

Another idea:

This is really weird, but maybe you protonate one of the oxygens on the carboxylic acid until it leaves as water, forming a really unstable (super electrophilic) cation, which will be a good enough electrophile for an electrophilic aromatic substitution reaction with the benzene ring?

 

[FROGGBUSTER]

Another idea:

This is really weird, but maybe you protonate one of the oxygens on the carboxylic acid until it leaves as water, forming a really unstable (super electrophilic) cation, which will be a good enough electrophile for an electrophilic aromatic substitution reaction with the benzene ring?

I asked around, and apparently this is correct.

 

[FROGGBUSTER]

Seriously? Weird. I don't think I like that problem if that is the correct mechanism. What book is it from?

EK 1001 OChem questions. It has more than a few mistakes in it though, so I dunno.