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Questions tagged [chemoselectivity]

For questions about selectivity between different functional groups.

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17 votes
1 answer
22k views

Why do BH3 and NaBH4 have different selectivities?

I've always known borane ($\ce{BH3}$), as a reagent for alkene hydroboration. Recently in class we talked about its use in the reduction of carboxylic acids to alcohols as well. Now obviously $\ce{...
0 votes
1 answer
46 views

Performing a reaction on one side of piperazine ring

I want to perform a reaction on one nitrogen of piperazine ring while avoiding the reaction on both nitrogens, I am familiar with Boc piperazine however it's expensive and would take 2-3 months to ...
1 vote
1 answer
184 views

Can organocuprates do SN2 reactions with tosylates?

In the presence of isolated ketones, can organocuprates add to secondary tosylates in an SN2 fashion without adding to the ketones?
0 votes
1 answer
390 views

Selectivity in dehydration of isopropyl alcohol to diisopropyl ether

Can isopropyl alcohol be dehydrated by sulfuric acid to diisopropyl ether in a similar way as to how ethanol can? Is there a way to avoid or at least minimize the inevitable dehydration to propylene?
15 votes
2 answers
4k views

Why does magnesium prefer to insert into C–Br bonds over C–Cl bonds?

In the formation of a Grignard reagent from a compound possessing both bromine and chlorine, magnesium preferentially inserts into the C–Br bond over the C–Cl bond. For example, the formation of a ...
4 votes
1 answer
971 views

nBuLi and tBuLi can take part in halogen metal exchange OR deprotonate. Is there any way to predict which it favours?

I have included a synarchive pathway: https://synarchive.com/syn/144 where BuLi favours deprotonation over halogen metal exchange
7 votes
0 answers
489 views

Why do poisoned catalysts (Lindlar, nickel borate) result in partial hydrogenation of alkynes?

I read that alkene is more reactive than alkyne, so in hydrogenation of alkynes, it's difficult to isolate the alkenes. But with poisoned catalysts like Lindlar's catalyst or Nickel-Boron (Ni2B), they ...
0 votes
0 answers
103 views

Selectivity in Thermodynamically-Driven Silyl Enol Ether Formation, and Optimistic Avoidance of Protecting Group Chemistry

I am aware of the regioselectivity of silyl enol ether formation at an unsymmetrical ketone under 'thermodynamic conditions'. Does this selectivity extend to systems containing more than one ketone ...
1 vote
0 answers
81 views

Reagent to reduce aliphatic aldehyde to alcohol while protecting double bond

I have a straight chain, aliphatic aldehyde (liquid) with a double bond in it. I want to reduce the terminal carbonyl group to an alcohol but without touching the C=C double bond. The double bond is ...
9 votes
2 answers
4k views

m-CPBA Selectivity between Baeyer Villiger Oxidation and Epoxidation?

If both a ketone and an alkene are present in a molecule and you add one equivalent of m-CPBA, what are the factors that determine which group will be oxidized, the ketone through Baeyer-Villiger ...
1 vote
2 answers
502 views

Will a Grignard reagent react with an epoxide or episulfide first? [closed]

In this question, I am confused whether the Grignard reagent will attack the epoxide or the episulfide (thiirane) first. The solution says ring opening of the episulfide will occur due to greater ...
4 votes
1 answer
680 views

Are alkenes or alkynes reduced first with diimide?

I know that $\ce{NH2NH2}/\ce{H2O2}$ is used as an reducing agent for selective reduction of alkenes and alkynes. $\ce{NH2NH2}$ reacts with $\ce{H2O2}$ to form diimide ($\ce{N2H2}$), which then ...
2 votes
0 answers
76 views

Do tertiary ethers tolerate oxidative workup of an ozonolysis reaction?

I am attempting to cleave a double bond into a carboxylic acid and carbon dioxide using an ozonolysis reaction followed by an oxidative workup. I am concerned with the presence of a tertiary ether in ...
2 votes
0 answers
87 views

Can Weinreb amides be used to form 1,3 dicarbonyl compounds?

Weinreb amides are useful in reducing acid chlorides (and esters) to form ketones due to the fact that the more reactive keto group is unmasked only after treatment with acid and water, which destroys ...
6 votes
1 answer
88 views

Selective transfer of least/most stable anion from organometallic reagents

When heterocuprate reagents participate in conjugate addition, the least stable anion is transferred from copper to the electrophile: On the other hand, palladium-catalysed cross-coupling reactions ...
18 votes
2 answers
27k views

Why are fluorides more reactive in nucleophilic aromatic substitutions than bromides?

In nucleophilic aromatic substitution reactions, why do fluorides react faster than bromides? Ordinarily bromide is a better leaving group than fluoride, e.g. in $\mathrm{S_N2}$ reactions, so why isn'...
5 votes
1 answer
5k views

Why does the Rosenmund reduction stop at the aldehyde stage?

In the Rosenmund reduction, an acyl chloride can be reduced to an aldehyde by hydrogenation over a palladium catalyst poisoned with barium sulfate. Why isn't the aldehyde product further reduced to ...
5 votes
1 answer
14k views

Chemoselectivity in reduction of 3′-nitroacetophenone

When 3′-nitroacetophenone is treated with sodium borohydride, only the carbonyl group is reduced (top); however, when reacted with tin and hydrochloric acid only the nitro group is reduced (bottom). ...
1 vote
1 answer
658 views

Can an ether be selectively hydrolysed in the presence of an ester?

What reaction, or protection/deprotection can be used to transform the ether group of a molecule that also has an ester compound into an alcohol while keeping the ester unchanged? For example: The ...
6 votes
1 answer
3k views

Can a benzyl ether be removed in the presence of an ester?

I'd like to deprotect a benzyl group for a Fráter–Seebach alkylation. Would it be possible to do this with a Birch reduction using Li/NH3 (or Na/NH3), without also reducing the ester carbonyl group? ...
12 votes
1 answer
3k views

Monoepoxidation of 1,2-dimethylcyclohexa-1,4-diene using m-CPBA

What is the product formed when 1,2-dimethylcyclohexa-1,4-diene undergoes epoxidation with one equivalent of m-CPBA (meta-chloroperbenzoic acid)? In the epoxidation mechanism, the π-electrons ...
8 votes
2 answers
3k views

How can an aromatic ketone be reduced in the presence of a nitro group?

Is it possible to reduce an acyl group to an alkane, but still keep a nitro group intact without its reduction to an amino group? A Clemmensen reduction would reduce the nitro group, and it seems like ...
7 votes
1 answer
1k views

Selective alkylation of carboxylic acid versus phenol

Starting from the ketone shown, I plan to use a haloform reaction to transform the acetyl group into a carboxylic acid. Following that, there are two alkylations to be carried out: one esterification ...
16 votes
3 answers
6k views

Why does bromine add to a double bond instead of a triple bond if both are present?

According to my textbook, the addition of bromine to pent-1-en-4-yne at low temperature yields 4,5-dibromopent-1-yne: Why does bromination of the double bond occur selectively?
12 votes
1 answer
724 views

Single electron reduction of ketone by Na or Zn

Whenever we add Na or Zn metal to a ketone, why does the electron prefer to attack the carbonyl bond and form a radical, instead of removing the acidic hydrogen and forming an enolate and $\ce{H2}$ ...
6 votes
1 answer
940 views

Why is the nitrile group not hydrolyzed as well during hydrolysis of imine in Thorpe reaction?

while imine is getting hydrolysed, why does not nitrile group hydrolyse to give carboxylic acid?
5 votes
1 answer
3k views

Why is a Grignard reagent not protonated by chloramine?

When $\ce{RMgX}$ (Grignard reagent) reacts with chloramine ($\ce{NH2Cl}$) it forms $\ce{RNH2}$. But why doesn't it form $\ce{RH}$ by taking a hydrogen atom from chloramine as the negative charge so ...
2 votes
1 answer
3k views

Reaction of hydrazine and hydroxylamines with carboxylic acids

Carboxylic acids and their derivatives on reaction with hydroxylamine $\ce{NH2OH}$ and hydrazine $\ce{N2H4}$ give hydroxamic acids and acid hydrazides, respectively, through acyl nucleophilic ...
9 votes
1 answer
793 views

How can a ketone be enantioselectively reduced, in the presence of an ester?

I'd like to reduce enantioselectively a ketone in presence of an ester (which should NOT be reduced to an aldehyde and further to an alcohol). Adding $\ce{LiAlH4}$ would also reduce the ester and ...
6 votes
1 answer
7k views

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 ...
5 votes
2 answers
8k views

Reduction of a ketone in the presence of an aldehyde

An aldehyde group can easily be reduced to an alcohol using the mild reducing agent $\ce{NaBH4}$ at low temperature in the presence of a ketone group. This chemoselectivity is due to the fact that an ...