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35 votes
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Which is the currently accepted mechanism of a Wittig reaction?

tl;dr: I don't think there is any mechanism that is 100% correct, and, in cases like this especially, I think it would completely depend upon what set of carbonyl/ylid/base/solvent etc. was used. But, ...
NotEvans.'s user avatar
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11 votes
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Wittig versus Corey–Chaykovsky reaction

Overview of mechanisms There have been recent excellent summaries of the reaction profiles of the Wittig1 and the Corey–Chaykovsky2 reactions. For the purposes of answering this question, there's no ...
orthocresol's user avatar
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10 votes
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Why do stabilised ylids lead to trans alkenes in the Wittig reaction?

TL;DR: With stabilised ylids, the trans oxaphosphetane is formed, under kinetic control. This is due to minimisation of dipole-dipole repulsions in the transition state for oxaphosphetane formation: ...
orthocresol's user avatar
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9 votes
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What will be the major product of the reaction between (2R,3R)-2,3-dimethyloxirane and triphenylphosphine?

First, note that with the mechanism you have drawn you should expect to get a mixture of cis and trans isomers. In the intermediate you drew, rotation about the C–C bond will be fast and will lead to ...
orthocresol's user avatar
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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 ...
Buttonwood's user avatar
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8 votes
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Reagent choice in the formation of Wittig reagent

I am fairly sure that for both, there are practicality issues at hand. This is almost certainly so for the choice of phosphine. Even though PPh3 is absolutely terrible from an atom economy point of ...
orthocresol's user avatar
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6 votes

Which is the currently accepted mechanism of a Wittig reaction?

The Wittig reaction has been known for decades, but research into its mechanism has continued to throw up surprises even until now. The literature is unfortunately very difficult to read, as numerous ...
orthocresol's user avatar
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6 votes

What will be the major product of the reaction between (2R,3R)-2,3-dimethyloxirane and triphenylphosphine?

Think about how the PPh3 first reacts with the epoxide - it does a nucleophilic attack on one of the carbons from below the epoxide ring to give the intermediate shown below left (I have drawn the P ...
Waylander's user avatar
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3 votes

H-NMR: Why are coupling and integration values not matching?

I finally found the answer to my question on page 88 of supporting information to the first reference[1], which gives the $^1\ce{H}$-NMR data as follows: $(\pu{400 MHz}, \ce{CDCl3})$: 7.75-7.20 (m, ...
jona173's user avatar
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3 votes
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Wittig reaction in presence of carboxylic acids

This works because the acidic starting material is going to be deprotonated as there is excess bicarbonate present. Because of the adjacent carboxylate group, the pKa of the phosphonium species is ...
Waylander's user avatar
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3 votes

Reagent choice in the formation of Wittig reagent

Wittig reactions can be performed with all sorts of phosphanes. The resulting phosphonium salts can be deprotonated by all sorts of bases, as long as the base is basic enough. Triphenylphosphane has ...
Jan's user avatar
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2 votes

Wittig reaction with an alkyl dibromide

It seems that the method to circumvent this problem is indeed to use a protecting group to protect one end of the alkyl chain, which is the end to be converted to a bromide after the Wittig reaction. ...
Tan Yong Boon's user avatar
2 votes

What is the function of PhLi in this reaction?

I was wrong, this is not a Wittig reaction. Just posting the answer to let anybody who comes in hunt for this in the near future. On googling for about an hour, I discovered that this is indeed a ...
prog_SAHIL's user avatar
1 vote

how can i synthesis unsaturated ester via wittig reaction?

A good system for this is using DBU as the base in refluxing chloroform. Bull. Chem. Soc. Japan (2003) 76 1675
Waylander's user avatar
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