9 votes
Accepted

What is the reaction mechanism between acetophenone and ethyl phenylpropiolate to form a 2-pyrone?

The general idea in the answer above is correct, but some of the details need to be looked at more closely. The first step is as drawn in the original post. Deprotonation of the ketone, followed by ...
orthocresol's user avatar
  • 70.9k
8 votes
Accepted

Role of NaI in Formation of Silyl Enol Ethers using Chloro(trimethyl)silane

The use of $\ce{NaI}$ in $\ce{MeCN}$ (a solvent in which $\ce{NaI}$ is quite soluble) is forming $\ce{Me3SiI}$ from the $\ce{Me3SiCl}$. The reason for doing this is $\ce{Me3SiI}$ is significantly more ...
Waylander's user avatar
  • 21.9k
6 votes
Accepted

Mechanism of acid-catalyzed Robinson annulation?

As I mentioned in my Comment the only serious issue was the formation of an allylic anion in acid medium. You seem to know how to form enols from ketones and how to form ketones from enols. I will ...
user55119's user avatar
  • 16.5k
5 votes

Nucleophilicity of sterically hindered enolates

One thing that will help you understand how this can happen at a position that otherwise looks hindered is to consider the geometry at that position. Carbon 2 is planar in the enolate anion, and the ...
Ben Norris's user avatar
  • 42.8k
5 votes

What is the reaction mechanism between acetophenone and ethyl phenylpropiolate to form a 2-pyrone?

Your attempted mechanism is correct. There is an active $\ce{\alpha-H}$ in the your final intermediate ($2$ $\ce{-COOEt}$s are present on the carbon (well one of them is attached indirectly, but it ...
napstablook's user avatar
  • 1,514
4 votes
Accepted

Selective formation of enolates

A few comments are in order as to the way in which the enolate formation is conducted. Lithium diisopropylamide (LDA) is formed in situ from the free amine and n-BuLi at -78oC at which temperature the ...
user55119's user avatar
  • 16.5k
4 votes
Accepted

Enolate ion opening an epoxide?

Never say never! :-) Here is the answer for your question (Ref.1): Abstract: We report here that (1) enolate anions of five- to seven-membered cycloalkanones nucleophilically open cyclopentene and ...
Mathew Mahindaratne's user avatar
4 votes
Accepted

How does base size affect the ratio of kinetic/thermodynamic enolate?

One problem with comparing product ratios using $\ce{LiN($i$Pr)2}$ vs $\ce{Ph3CLi}$ is that it's not really an apples-to-apples comparison - one is a lithium amide base, whereas the other is a ...
Organic Chemistry Explained's user avatar
3 votes
Accepted

Acidity of alpha hydrogens in enolate formation

I'm interested in the OP's curiosity. I'd agree with Waylander about disfavoring to make 4-membered rings. Yet, it is possible to have two six-membered ring products. The first $\alpha$-proton ...
Mathew Mahindaratne's user avatar
3 votes

Can R-3-methyl-4-heptanone be enantioselectively synthesised from 4-heptanone?

Enders SAMP/RAMP hydrazone chemistry will do this(1). The Wikipedia article on this technique is a good introduction: (1): Corey, E. J.; Enders, D. (1976). "Applications of N,N-dimethylhydrazones to ...
Waylander's user avatar
  • 21.9k
3 votes
Accepted

how is the esterification of amino acid carried on in this reaction

I think you need a protection strategy and there are several choices. This one uses O'Donnell's benzophenone imine strategy details here. First you prepare glycine ethyl ester hydrochloride from ...
Waylander's user avatar
  • 21.9k
3 votes
Accepted

stereoselectivity in aldol reactions

I do not have the recent or the fifth edition of Advanced Organic Chemistry: Part B but have the forth edition (Ref.1) to answer this question. First, this book is not for for studying stereochemistry,...
Mathew Mahindaratne's user avatar
3 votes

Nucleophilicity of sterically hindered enolates

Although Ben Norris has given excellent explanation for why the steric hindrence is not playing the role in the reaction of cyclohexanone with excess methyl iodide to give tetramethylated ...
Mathew Mahindaratne's user avatar
2 votes
Accepted

Mechanism of deprotection of enol thioether

Mechanism: 1 -hydroxide anion adds to the =CHSBu carbon in a Michael addition giving the enolate anion of the carbonyl and -CHOH(SBu). 2- The enolate anion deprotonates the newly arrived -OH group to ...
Waylander's user avatar
  • 21.9k
2 votes

how does enolate affect an elimination reaction?

Both can occur, but the top drawing allows for easier formation of a "free" electron pair. In general breaking C-C, C-N, etc. bonds has a rather high activation energy barrier, so the direct ...
WaveInPlace's user avatar
2 votes
Accepted

Grignard reagent will act as a base or a nucleophile

As most of us chemists have understood and experienced, the Grignard reagent have undergone the many reactions with suitable substrates. Yet, the most familiar and probably the most used reaction is ...
Mathew Mahindaratne's user avatar
2 votes
Accepted

Nucleophilicity of sterically hindered enolates

The permethylation of cyclohexanone with KH/MeI is described here JOC paper. The yield quoted is 96% and other ketones are also exemplified.
Waylander's user avatar
  • 21.9k
2 votes

Why can't the N- end of the nitrile anion attack the alkyl halide in an SN2 fashion during an alkylation reaction when OH- can?

It can. According to this JACS paper here steric effects are a major factor in whether the ketenimine is formed or the C-alklyated product - the more hindered the nitrile, the more N-alkylation.
Waylander's user avatar
  • 21.9k
1 vote

Acidity of alpha hydrogens in enolate formation

The two deprotonated species are in equilibrium (along with the neutral parent molecule). The deprotonation you suggest will occur, but the forward reaction cannot because it would be forming a [4] ...
Waylander's user avatar
  • 21.9k
1 vote

Which of the following compounds possess more than one percent enol content?

All the compounds that have a relation $\alpha-\beta$ between the carbonyl groups. The hydrogen between two $\ce{CO}$ is very acid because two electrowithdrawing remove electron density from the $\ce{...
Jonny_92's user avatar
  • 195
1 vote

How would I synthesize ethyl 2‐oxocyclohexane‐1‐carboxylate from cyclohexanone?

As you will see if you look at the reference mentioned by @Mathew-Mahindaratne, the standard conditions for this transformation is NaH/KH in THF at reflux with diethyl carbonate (EtOCOOEt) with an ...
Waylander's user avatar
  • 21.9k
1 vote

Less substituted vs more substituted alkene

I'll address your concerns about alkene stability in general and enamines in particular. It is useful to examine the acyclic permutations of C6H12. The heat of formation of these isomers is a good ...
user55119's user avatar
  • 16.5k

Only top scored, non community-wiki answers of a minimum length are eligible