Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: adianadiadi on 30/09/2013 15:48:10

Title: Wittig reaction - unaffected functional groups
Post by: adianadiadi on 30/09/2013 15:48:10

I would like to know what are the functional groups that are not affected by wittig reaction conditions?

Title: Re: Wittig reaction - unaffected functional groups
Post by: chiralSPO on 30/09/2013 19:22:39

There are many functional groups not affected, including carboxylic acids (which are only deprotonated under the wittig conditions), esters, amides, amidines, ureas etc.

Really it is easier to ask which groups DO react: aldehydes and sterically unencumbered ketones will undergo a wittig condensation. Any compound that has an acidic proton (pKa <20) is likely to be deprotonated under these conditions. Similarly alkyl halides (Cl, Br, I, OTf, OMs, OTs) can potentially undergo E2 eleminitation reactions to produce alkenes.

Title: Re: Wittig reaction - unaffected functional groups
Post by: adianadiadi on 02/10/2013 16:36:36

Thank you. I would like to know why not the carbonyl group of esters could also react? Any explanation?

Title: Re: Wittig reaction - unaffected functional groups
Post by: chiralSPO on 02/10/2013 20:10:25

The carbonyl in esters, carboxylic acids and amides are less electrophilic because the electron density on the oxygen or nitrogen is donated into the carbonyl pi system.

Esters are not electrophilic enough to react with phosphorus-based Witting- or HWE-type olefination reagents, however the more reactive metal-based reagents like Tebbe and Petasis can react with esters too.

Title: Re: Wittig reaction - unaffected functional groups
Post by: adianadiadi on 07/10/2013 04:14:36

Thank you @chiralSPO