17
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; acidic conditions could result in protonation of the tertiary alcohol product and elimination to the alkene. It also ensures that all inorganic salts of Mg ...
16
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: "Recall that epoxides rearrange with Lewis acid...". It is common that catalytic Lewis acids rearrange 2,3-dialkyl oxiranes [epoxides] to ketones. In the case of ...
15
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 (organocopper reagents) add to the beta-position of an unsaturated ketone.
This exact transformation was reported by Akai and coworkers recently (Org. Lett. 2010, 12, ...
12
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 industrial use was established.
One of the recent reviews in hydrogen-storage applications [2, p. 220] compares the older two-step process of $\ce{MgH2}$ synthesis:
...
12
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 is not only dependent on $\ce{X}$, but also on the solvent:
$$\ce{2RMgX <=> R2Mg + MgX2}$$
There also have been some dimeric structures reported, i.e. ...
9
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 regioselectivity may be explained by the preference of a five-membered chelate ring over a four-membered one; and
the stereoselectivity arises because syn addition ...
9
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 is no obvious way to get it back (there is a way)
More seriously, Grignard reagents are pretty terrible for $\text{S}_N 2$ reactions. They are very strong bases,...
7
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 about anything that might make the proton vulnerable. Attaching the proton to an electronegative atom like nitrogen is enough, so primary and even secondary ...
7
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), pp 1411–1416. The table of data shown below is hard to read without including more of the text, but it was found that at 66 C in THF, after 5-10 minutes, 41% of ...
7
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 from aryl organometallics with much better yields.
7
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 course. Magnesium powder may prove to have more of an oxide film than turnings and hence be less reactive. Most Grignard preps use turnings. It might be helpful ...
7
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 states
The reaction between sulfur dioxide and Grignard reagent has been widely used for the preparation of aromatic and aliphatic sulfinic acids.
I would ...
6
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 an "active" form of magnesium hydride in THF. They act as hydride ion sources for reaction with $\ce{AlH3}$ and $\ce{BH3}$ (forming mixed ...
6
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 but there are examples of additions to alcohols (see the JoC reference)
5
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 alternative is there, due to lack of a decent leaving group, so deprotonation ultimately prevails; but $\ce{NH2Cl}$ allows displacement of a chloride ion and thus ...
5
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 say the magnesium reacts at position 1. Then the negative charge would couple with the conjugated triple bond to spread to position 3:
$\ce{Br\overset{+}{Mg}\...
5
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 acids. For example, if you look at esterification, carboxylic acid and alcohol first make an addition, giving tetrahedral intermediates 1 and 2. Intermediate 2 ...
4
In terms of regioselectivity, at least for the first addition of the Grignard reagent, I suggest to have a look on the cumarin, that may be seen as an α,β-unsaturated carbonyl compound. Hard nucleophiles (in terms of HSAB principle) like $\ce{MeLi}$ would almost exclusively react with the carbonyl carbon, as you drew in your reaction equation. Soft ...
4
Ben is right that your product is simple dimer of substrate. However, there is much easier approach to conduct dimersisation of butene - it happens easily if you use strongly acidic catalyst, like conc. sulfuric acid or ion-exchange resin, such reaction is used for example in production of isooctane. It's similar to cationic polymerization of alkenes, so ...
4
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 electrophiles. Grignard reagents will generally go for 1,2-attack instead. See this Wikipedia article for more info:
4
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 metallation of the aryl halides to form the aryl lithium or Grignard and reaction with a trialkyl borate $\ce{B(OR)3}$, or by Pd catalysed reaction with pinacol ...
4
Aromatic nitro groups are not compatible with Grignards as they react with the nitro group. An example of this being useful is the Bartoli synthesis of indoles from vinyl Grignards (Tet. Letts. 1989, 30 2129, Curr. Org. Chem.. 2005, 9, 163). The first step of the Bartoli is addition of the vinyl Grignard to the O of the N=O of the nitro group so I presume ...
4
The electronegativity difference between carbon and the halogen used for Grignard reagents is actually not all that high. Alkyl fluorides are generally un-reactive towards magnesium, and other halogen whose alkyl compounds are more reactive have electronegativity ranging from only a few tenths above carbon to a few tenths below carbon.
In any event the ...
4
THF has a number of differences with diethyl ether:
Oxygen non-bonding doublets are more available for bonding with magnesium because the 2 ethyl groups are not freely rotating around (you may think of THF as diethyl ether with its arms tied in its back).
THF boils at 66°C (ether 34.6°C). Because the reaction is usually carried out so to maintain a gentle ...
4
You should look at two things:
1) Will the reaction stay on course? If you add water to the Grignard reagent first, without the carbon dioxide initially, what do you get? Is it something that will get you your carboxylic acid when you add the carbon dioxide?
2) Can you make the Grignard reagent to begin with? Here again you are asking the reaction to ...
4
The problem is with the free $\ce{NH}$. Grignard reagents are strong bases ($\mathrm{p}K_\mathrm{a}\sim 50$), strong enough to deprotonate $\ce{R2NH}$. Any Grignard that formed would be immediately quenched by the free $\ce{NH}$. You need to protect, this is typically done with tBOC, more discussion here.
3
I've done this with aromatic Grignards, but I have no reference and no database access any longer.
I think when I did it, I was relying on an older colleague's instructions. It was pretty much generate your Grignard from ArBr + Mg in THF, cool in ice bath, stir vigorously and add elemental sulfur. You may need to introduce a reductive step as you can ...
3
This is not a 1,4 addition. It is a 1,2 addition across a carbon-carbon double bond. This mode of reaction is unusual for Grignard reagents, but here a highly stabilized "double benzylic" anion is formed and the competitive reaction of adding to the carbonyl group is sterically hindered.
3
I have supplied a diagram that is more legible than the small one you have provided. The cis stereochemistry of the product is a function of axial, but not equatorial attack of the reagent. The stereochemistry is established after the addition occurs. Structures 1 and 2 illustrate the "chair-chair" interconversions of the cyclohexene ring. As the C-C bond is ...
3
A search of Chemical Abstracts for the OP's reaction of coumarin 5 with phenyl magnesium bromide forming 2,2-diphenyl-2H-chromene had 216 substructure hits but none from coumarin itself. Two typical examples are shown below.1 Suraj S is vindicated!
Although the OP's professor's proposed product 10 of the reaction is well-known, a search did not produce its ...
Only top voted, non community-wiki answers of a minimum length are eligible
