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Questions tagged [aldol-reaction]

This tag should be applied to questions about mechanisms, selectivity, or other aspects of aldol reactions.

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Strong base use in aldol condensation

Why is a strong base required for an aldol condensation reaction to deprotonate the α carbon of the carbonyl? Isn't the α carbon acidic due to the negatively charged enolate ion that forms being ...
6
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1answer
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How does this ring expansion on a steroid system occur?

The correct answer is supposedly B, as shown by Gravestock et al.[1] In this reaction after ozonolysis of the C=C double bond, two ketones are formed. How is a rearrangement or expansion of the ring ...
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Claisen-like condensation with acid chloride

In the Claisen condensation, an ester enolate attacks an ester, with an alkoxide anion leaving subsequently to give a $\beta$-keto ester. Is it possible for a typical enolate of an aldehyde or ketone ...
3
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1answer
87 views

Why cyclohexane-1,4-dicarbaldehyde does not give aldol condensation?

I was recently came to know as a fact that cyclohexane-1,4-dicarbaldehyde does not give the aldol condensation reaction in spite of possessing α-hydrogens. I was told that this is due to steric ...
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Selectivity of aldol in base catalysed medium

Now this question has troubled me for quite some time. I know about the reason B is formed in acid catalysed medium. But why is A major in base catalysed medium? According to me with weak bases like $...
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Do all condensation reactions involve addition and elimination?

We have been recently taught about organic condensation reactions, where one group attacks another compound, and finally a small group is released/eliminated. An example would be the Aldol ...
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540 views

P2NP synthesis ammonium acetate catalyst?

I am going to try to prepare some P2NP from benzaldehyde and nitroethane following this procedure: The aldehyde (5g), 5 ml. of the nitroalkane, and 2g of ammonium acetate were added to 20 ml of ...
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1answer
59 views

Aldol Condensation with Cyclic Molecule [closed]

How does one solve this mechanism? Why doesn't the negatively charged oxygen on the non-cyclic molecule remove an alpha hydrogen from the cyclic one?
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1answer
122 views

Selectivity in aldol condensation of 7-oxo(6,6-²H₂)octanal

I am supposed to find the product of the following reaction: I know that six-membered rings are more stable than five-membered rings, but the C-D bonds are stronger, so it confuses me where will the ...
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2answers
168 views

Product of an intramolecular aldol condensation

When nonane-2,8-dione is treated with base, the product 1-(2-methylcyclopent-1-en-1-yl)ethan-1-one forms according to the following scheme: The arrow denotes the hydrogen that is first attacked by the ...
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1answer
56 views

Is one syn aldol product preferentially formed over the other?

In Carruthers' Modern Methods of Organic Synthesis, the following aldol reactions of two (Z)-enolates with benzaldehyde are shown: The two transition states shown seem to be different, and lead to ...
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1answer
119 views

Base-promoted rearrangement of β-ketoester

Propose a reasonable mechanism for the following transformation: I guess an enolate probably forms first, but then what does it attack to give something like the product in the question?
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Acidity of aldehydes and ketones and enolate formation

In most academic courses you'd learn that aldehydes are more acidic (lower $\text{p}K_\text{a}$) than ketones due to the lower electron donating effect of the proton compared to the alkyl group of the ...
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2answers
143 views

Which Alpha-H will be extracted in intramolecular condensation rxn between ester and ketone

In this problem, which hydrogen will be extracted - the one near the ketone group (Marked 2) or the one near the ester (Marked 1)? My approach:- In intramolecular reactions between aldehydes and ...
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125 views

Retro-aldol reaction (glucose 1,6-bisphosphate)

I am interested if glucose 1,6-bisphosphate can undergo aldol cleavage (retro-aldol reaction) and result in the formation of a two-carbon and a four-carbon compound. I think 1,6-bisphosphate can not ...
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1answer
197 views

Regioselectivity in Claisen condensation and aldol reaction

I'm having a hard time determining regio-selectivity in those two reactions. At the image above I've drawn one example for each on of them. My question is how do we choose where the deprotonation ...
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Why are lithium (Z)-enolates more stereoselective than (E)-enolates in aldol reactions?

In aldol reactions, it is apparently a general rule of thumb that (Z)-enolates give higher stereoselectivity (for the syn aldol product) than (E)-enolates do for the anti product. Quoting Carey & ...
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1answer
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Deciding which α-Η gets abstracted in aldol condensation

Consider the base catalysed aldol condensation of methyl ethyl ketone. The first step involves the abstraction of a proton by the base. However I am having trouble deciding whether the proton will be ...
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1answer
116 views

Chelation-controlled aldol: why is the α substituent pseudo-axial?

In this Mukaiyama aldol reaction, taken from a 1999 paper by D.A. Evans,1 when $\ce{TiCl4}$ was used as the Lewis acid catalyst, the aldehyde 4a formed a chelated intermediate whereas 4b did not (due ...
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65 views

Can aldol reaction occur during α-halogenation of ketone?

I know both aldol and $\alpha$-halogenation reaction well. I know that in and aldol reaction, the carbonyl containing molecules like ketones and aldehydes attacks themselves when base like $\ce{OH-}$...
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1answer
294 views

What products did this aldol condensation create?

I followed a procedure in my organic chemistry lab, but I don't understand what product the procedure created. Can someone tell me what chemicals reacts with which to create the product? First $\ce{...
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2answers
1k views

Will cinnamaldehyde undergo self-aldol condensation?

Will cinnamaldehyde undergo self-aldol condensation? My book says it won't but since it has an α-hydrogen, I'm confused.
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2answers
212 views

Regioselectivity of deprotonation of 1,4-dicarbonyl

In the intramolecular aldol condensation of hexane-2,4-dione (above), why does the base abstract one of the $\ce{-CH3}$ protons instead of one of the $\ce{-CH2}$ protons? Both sets of protons are α to ...
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1answer
476 views

Will 2-methylbutanal undergo aldol condensation

Will 2-methylbutanal undergo aldol condensation? We are taught that it will not because the +I effect makes the carbanion unstable, but if we make an enolate ion, isn't it resonance stabilized by the ...
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2answers
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Self aldol condensation of butanal under basic conditions

The reaction is such: I've counted the number of carbons on each side: LHS=4, RHS=8 My working is such:
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2answers
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Product of intramolecular aldol condensation of 3-methyloctane-2,7-dione

What is the major product formed when 3-methyloctane-2,7-dione is treated with sodium hydroxide? My main issue is where the base deprotonates. Two enolates are possible (I neglected the other ...
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2answers
202 views

High diastereoselectivity of Zr, Sn(II) and Ti enolates

Why do zirconium, tin(II) and titanium enolates always afford syn-aldol products with high stereoselectively when they react with other carbonyl compounds?
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1answer
651 views

Why does acetate aldol with Evans auxiliary give almost no diasteroselectivity?

The following acetate aldol reaction gives no diasteroselectivity: Because I don't know what the basis of above statement is (I heard it in a lecture and read it on some internet web pages), I expect ...
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1answer
149 views

What determines whether an aldol reaction will occur again or eliminate?

The product of an aldol reaction is a $\beta$-hydroxy ketone. This can go on to eliminate to form an alkene thus: However, the species on the far left of the above diagram (the $\beta$-hydroxy ketone ...
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0answers
118 views

Does the amine used to generate the enolate affect the selectivity of an Evans aldol reaction?

In an Evans aldol reaction, the enolate is typically generated by addition of a boron Lewis acid (e.g. $\ce{(n-Bu)2BOTf}$) and an amine, which acts as a weak base. I'd like to know whether there's any ...
6
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3answers
296 views

Aldol of 7-oxooctanal

I want to do intramolecular aldol condensation of 7-oxooctanal: I am talking about the major product. Clearly, a 6-membered ring would be a major product, but there are 2 possibilities: taking ...
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1answer
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Does aldol condensation give different products in different conditions?

I know the mechanism of aldol condensation and general method to determine products in crossed aldol reactions, or reactions between dissimilar molecules. But the following statement in my class notes ...
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1answer
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Selectivity in aldol condensation between pivaldehyde and acetone

In a crossed aldol condensation (condensation between aldehyde and a ketone), the primary products are such, that the carbonyl group of the ketone remains intact, and the $\alpha$-hydrogen of ketone ...
7
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1answer
2k views

What is the product formed in the reaction of dimedone and benzaldehyde?

I'm having a hard time deducing the structure of the product formed when dimedone and benzaldehyde react in the presence of catalytic piperidine. I think that a Knoevenagel reaction will get me to ...