Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: sharbeldam on March 22, 2020, 03:59:56 PM
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So since I cant do the friedel craft for 2 reasons:
1) the alkene will react with the catalyst
2) also the R groups are o/p directing and I need to add an ethyl group to the meta position.
Here is my try but it seems too long, any simpler ways? what's wrong with my way?
Thank you so much! Image attached.
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I think you can turn the alkene to a carbonyl group using mild oxidative degradation condition which gives a meta directing group then you can add your ethyl group.
(https://cdn.masterorganicchemistry.com/wp-content/uploads/2019/12/6-mechanism-for-the-oxidative-cleavage-of-alkenes-with-o3.gif)
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So you want the meta ethyl styrene.
If You start with the acetanilide (o,p) director. Add a bromine with BR2/FeBr3. Add an ethyl by Friedel-Crafts. Now hydrolyze off the amide, diazotize the amine and treat with hypophosphorous acid (H3PO2) to replace the diazo with H. Now you have m-bromoethylbenzene. Treat with lithium metal or butyl lithium to make the m-ethyl phenyl lithium. Treat it with dimethylformamide to make the methylbenzaldehyde. Treat this with the ylid derived from a methyltriphenylphosphonium salt under Wittig conditions to make the alkene.
There may be a better way but this works well.
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Maybe you get halogen-dance if you try to get ethyl by Friedel-Craft when you have a bromo in the molecule hollytara? I dont understand the scheme, it is so complicated? To have a aldehyde as meta-director and use wittig to get the styrene is good I think though. Brominate benzaldehyde and use Pd-chemistry (Stille) with triethyl tin to get the ethyl and then wittig.
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I think that is good - I was trying to keep from going too advanced. In classic syntheses, you can use nitro (as a m director) or reduce to the amine (o,p director) to direct position of reaction, then remove the directing group by diazotizing and replacing with hydride from H3PO2.