22 votes
Accepted

Does a Grignard reagent react with enones to give the 1,2- or 1,4- product?

The correct answer is the 1,2-addition product (i.e. the allylic alcohol 1). In general, Grignard reagents and organolithium reagents add directly to the carbonyl carbon, while organocuprates (...
user avatar
  • 10.5k
22 votes
Accepted

What is the role of ammonium chloride in the workup of a Grignard reaction?

Ammonium chloride ($\ce{NH4Cl}$) is the work-up reagent that quenches the magnesium alkoxide product of the Grignard addition. It is the reagent of choice as it is a proton source without being acidic;...
user avatar
  • 19.1k
19 votes
Accepted

Ring contraction when cyclohexene oxide is treated with methyl Grignard

Sara Jane: Lest you miss the point of the stimulating discussion between Waylander and Zhe, I would like to sum up their thoughts with a diagram. Your first clue should have been the opening line: "...
user avatar
  • 13.7k
15 votes
Accepted

Are there any significant uses of the compound formed by magnesium and anthracene?

It seems like an idea of using magnesium anthracene systems for the $\ce{MgH2}$ production persisted since 1980s [1] till late 2000s, when new more efficient method with better scalability for ...
user avatar
  • 35.8k
13 votes

Does a Grignard reagent react with enones to give the 1,2- or 1,4- product?

The Grignard reaction, although very well examined, there are still arguments about the mechanism and the overall process. The reagent is usually best described via the Schlenk equilibrium, but that ...
user avatar
13 votes

Why are the products of Grignard reaction on an alpha-chiral ketone diastereomers rather than a racemate?

First of all, welcome to ChemSE on your first post. Allow me to expand on the Comment of Karsten Theis and provide you with an illustration. If a compound is racemic and bears a single stereocenter, ...
user avatar
  • 13.7k
12 votes
Accepted

Can Mg/ether reduce carbonyl groups?

It is known that $\ce{Mg}$ will reduce ketones. The articles (Ref.1 and 2) in the References section confirm this fact. If you want to form the Grignard reagent of a molecule that also happens to ...
user avatar
  • 19.1k
10 votes

Reaction of Grignard reagent with primary amines

Here's the thing about Grignard reagents. Though we typically want them to do nucleophilic addition to something, these powerful bases tend to go for protons -- a faster reaction -- if there is just ...
user avatar
  • 41.3k
10 votes
Accepted

Why do Grignard reagents add to propargyl alcohols?

The addition of Grignards to propargyl alcohols occurs via the alkoxide salt, after deprotonation:[1] Here: the reactivity may be explained by the stabilising influence of complexation; the ...
user avatar
  • 66.5k
9 votes
Accepted

Getting 3,4-dimethylhex-3-ene from but-2-ene

Your approach, which uses $\ce{Br2}$ to convert 2-butene into 2,3-dibromobutane and react that with ethylmagnesium bromide $\ce{CH3CH2MgBr}$ has two flaws: This approach removes the alkene and there ...
user avatar
  • 41.7k
9 votes
Accepted

Rearrangement of Grignard reagent formed from exocycloproyl vinyl bromide

Grignard reagents are capable of rearranging, especially in this situation where there is significant strain. The specific vinyl bromide you drew here has been studied: J. Org. Chem., 1974, 39 (10), ...
user avatar
9 votes
Accepted

Grignard reagent with sulfur dioxide

You get sulfinic acids $\ce{RSO2H}.$ This paper by Dowson et al. [1] states that Grignard plus $\ce{SO2}$ gives sulfinic acids and as a reference quotes an older article by Allen Jr. et al. [2] which ...
user avatar
  • 19.1k
9 votes
Accepted

Why do Grignard reagents act as sources of nucleophilic R− and not Br−?

In all likelihood the halide ion does attack the substrate. But, the product such a reaction mode would form does not accumulate whereas the alkylated product does. Recall that in a nucleophilic ...
user avatar
  • 41.3k
8 votes

Synthesis of (1S,2S,4S)-4-ethenyl-5-methylcyclohexane-1,2-diol

Because the target structure contains the motif of a cyclohexane-1,2-diol, I suggest an approach including a Diels-Alder reaction (DA in the illustration below) of 1,3-butadiene and the commercially ...
user avatar
  • 23.8k
8 votes

Can primary amine be produced using Grignard reagent?

Grignard reagents, in addition to being nucleophiles, are strong bases. Attempting to react a Grignard $\ce{RMgX}$ with nitrous acid is simply going to result in protonation of the Grignard to give $\...
user avatar
  • 19.1k
7 votes

Does Grignard reagent react with oxygen?

This paper says it does and notes that while the yield of alcohols from aliphatic Grignards is 60-90%, formation of phenols is much less satisfactory. Other methods exist for the formation of phenols ...
user avatar
  • 19.1k
7 votes
Accepted

Preparation of an aromatic Grignard reagent

I have prepared many aryl Grignards in my career. Generally the aryl bromide or iodide is easier than the chloride, but it can be done. THF is certainly fine for this, run under inert atmosphere, of ...
user avatar
  • 19.1k
7 votes
Accepted

Conversion from t-butanol to alkene

t-butanol + allyltrimethylsilane + Lewis acid This is called the Hosoni-Sakurai Reaction (see J. Org. Chem. 2006 71 8516) Can only find an image for the more common addition to carbonyl compounds ...
user avatar
  • 19.1k
7 votes
Accepted

Why are the products of Grignard reaction on an alpha-chiral ketone diastereomers rather than a racemate?

The reaction introduces a new chiral center into your mix, that chiral carbon being the one that has the tertiary alcohol on it (let’s call this #2). The product will produce a mixture of those chiral ...
user avatar
6 votes

Is HMgX also a Grignard Reagent like RMgX?

According to this reference $\ce{HMgX}$ compounds are a thing. You can't make them with magnesium +$\ce{HX}$, of course (what actually happens?), but you can get them from magnesium halide salts plus ...
user avatar
  • 41.3k
6 votes
Accepted

Grignard alkene on a carbonyl

Nucleophilic acetyl substitution is common among carboxylic acid, acid chlorides, anhydrides, esters, and amides. Two very common examples are anhydride decomposition and esterification of carboxylic ...
user avatar
6 votes
Accepted

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

There are quite a few reasons why the episulfide might open before the epoxide: Sulphur is less electronegative than oxygen. Therefore, by Bent's rule , more atomic s-character will be directed by ...
user avatar
  • 3,036
6 votes
Accepted

Priority order of attack of grignard reagents on functional groups

For the compound given in the question, the priority order of Grignard reagent attack follows, $\ce{R-OH > R-CO-R' > R-COOR'}$ Reason: Acid-base neutralisation are very fast. Carbonyl carbon ...
user avatar
  • 2,825
6 votes
Accepted

Grignard reaction with cycloheptatriene

The product A, shown below, is formed by first reducing the ketone to a secondary alcohol with $\ce{LiAlH_4}$ and then by adding a methyl group to form an ether using the reagent $\ce{CH_3I}$. $\...
user avatar
5 votes
Accepted

Phenol preparation from Grignard reagent

As requested by the OP - the route that lab chemists use to form phenols from aryl halides (not aryl fluorides) is via formation of the aryl boronic acid or boronate. These may be formed by either ...
user avatar
  • 19.1k
5 votes
Accepted

Why is a Grignard reagent not protonated by chloramine?

The $\ce{N-H}$ protons are relatively weakly acidic and this makes deprotonation kinetically less favored if an alternative nucleophilic attack mechanism is available. With $\ce{NH3}$ no such ...
user avatar
  • 41.3k
5 votes

What are the pros and cons of using Gilman reagent over Grignard reagent to synthesize a hydrocarbon?

I am not sure if Gilman reagents are harder to make than Grignard but they are softer nucleophiles and so they are used to perform 1,4-(conjugate) additions on $\ce\alpha,\beta-$unsaturated ...
user avatar
  • 1,536
5 votes
Accepted

Reaction of 1 equivalent of Mg in ether with 1,4-dibromobut-2-yne

Cyclobutyne cannot exist. There is no way to enforce 90° bends at both ends of a triple bond, but the carbanion formed by the Grignard reagent synthesis finds an easy way around this problem. Let's ...
user avatar
  • 41.3k
5 votes
Accepted

Addition of Methyl Grignard and use of HClO4 in this question

Consider the resonance structures of the pyranone. MeMgCl attacks the structure shown second. The perchloric acid workup hydrolyses the enol ether to give the diketone shown bottom right. NaOH ...
user avatar
  • 19.1k
5 votes
Accepted

Why does magnesium bromide transfers from a carbon atom to nitrogen in piperidine?

There is no step 1 and step 2 in this reaction. Both are consecutive and second one is fast because it is an acid-base reaction: Note that approximate $\mathrm{p}K_\mathrm{a}$ values of ring $\ce{C-H}...
user avatar

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