Chemistry Stack Exchange
Chemistry Stack Exchange

Questions tagged [aldol-reaction]

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

The aldol reaction is a common method in organic synthesis of forming new carbon carbon bonds, via the reaction of an enolate (a carbon nucleophile) into a carbonyl group (a carbon electrophile).

The products of aldol reactions are β-hydroxyketones (though they may undergo elimination to form the unsaturated ketone under certain conditions), with up to two new stereo centres formed. This 1,3-oxygenation pattern is found throughout natural products, making aldol reactions a versatile reaction in total synthesis.

Applicability of the tag:

  • All questions about the aldol reaction are necessarily about and should be tagged as such.
  • Depending on the nature of the question, additional tags such as or may also be appropriate.

Further reading:

Coverage of the aldol reaction can be found in any good organic chemistry textbook (see for suggestions). For more in-depth coverage, the following books should be consulted:

  • Mahrwald, R.; Modern Methods in Stereoselective Aldol Reactions; Wiley-VCH: Weinheim, 2013.
65 questions
17
votes
1 answer

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 the two products are formed as a racemic…
laminin
  • 3,385
  • 3
  • 23
  • 45
8
votes
2 answers

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 attack happen.
Jasmine
  • 379
  • 3
  • 13
8
votes
0 answers

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 & Sundberg, Advanced Organic Chemistry: Part B (5th…
orthocresol
  • 69,151
  • 11
  • 230
  • 391
8
votes
1 answer

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 baffles me: In presence of a base (alkaline…
stochastic13
  • 6,563
  • 6
  • 45
  • 74
8
votes
2 answers

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.
Mohd. AAMIR
  • 89
  • 1
  • 2
8
votes
1 answer

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 product of the first aldol reaction) can react…
RobChem
  • 9,606
  • 31
  • 78
  • 137
8
votes
2 answers

What does the intramolecular aldol condensation of 6-oxoheptanal form?

I know that when 6-oxoheptanal is treated with NaOH, an intramolecular aldol condensation will take place. But will a five-membered ring or seven-membered ring be formed? I know that the five-membered ring is more stable in comparison to the seven-…
Meet Patel
  • 95
  • 1
  • 4
7
votes
3 answers

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 hydrogen from $\ce{C^2}$ or $\ce{C^6}$. Which one would…
evil999man
  • 1,640
  • 1
  • 15
  • 24
7
votes
1 answer

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 this product: but the answer says that the product…
wolfik
  • 655
  • 1
  • 7
  • 5
7
votes
1 answer

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 possible, since carbocations are not formed as…
Kaushki
  • 109
  • 1
  • 6
6
votes
1 answer

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 will occur. My approach was that the base will…
Αντώνιος Κελεσίδης
  • 985
  • 7
  • 25
6
votes
1 answer

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 to the bulk of the TBS group). This was…
orthocresol
  • 69,151
  • 11
  • 230
  • 391
6
votes
1 answer

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 participates, i.e. gets removed by the base to…
stochastic13
  • 6,563
  • 6
  • 45
  • 74
6
votes
1 answer

Determination of major product in crossed aldol condensation

The title speaks for itself really. I know that if we have a conventional ketone (with 3+ α-hydrogens) and an aldehyde with less than or equal to 3 α-hydrogens, the ketone acts as the nucleophile and attacks the aldehyde, which consequently forms…
Arka Seth
  • 63
  • 1
  • 3
5
votes
1 answer

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?
Carlson Miller
  • 199
  • 5
1
2 3 4 5