The reaction of 2,3,5-trimethoxy bromobenzene with butyl lithium yielded the corresponding trimethoxybenzoic acid as an intermediate in a synthesis I
read earlier tody. I'm not seeing why.guy - 30-10-2007 at 21:53
Are you sure those are all of the steps?
The only thing that is possible is the formation of 1-Butyl-2,3,5-trimethoxybenzene. There are no other oxygens to make a benzoic acid. The only way
to get the benzoic acid is to oxidize the butyl side chain.Nicodem - 31-10-2007 at 00:48
Quote:
Originally posted by chemrox
The reaction of 2,3,5-trimethoxy bromobenzene with butyl lithium yielded the corresponding trimethoxybenzoic acid as an intermediate in a synthesis I
read earlier tody. I'm not seeing why.
The reaction of f BuLi with 1-bromo-2,3,5-trimethoxybenzene in THF at -78°C gives 2,3,5-trimethoxyphenyl lithium trough metal-halogen exchange
metathesis (a SET driven reaction). You omitted which reagent they used to prepare 2,3,5-trimethoxybenzoic acid from 2,3,5-trimethoxyphenyl lithium.
They could have introduced a fast stream of CO2 in the reaction mixture. Other possibilities are to quench the aryl lithium with excess dimethyl
carbonate or methyl cyanoformate, following by hydrolysis of the so formed methyl 2,3,5-trimethoxybenzoate. Direct lithiation of
1,2,4-trimethoxybenzene is no option here, since it would form 2,3,6-trimethoxyphenyl lithium, where lithium is coordinated with two MeO groups –
the reaction would result in the wrong benzoic acid, 2,3,6-trimethoxybenzoic acid. Hence the use of 1-bromo-2,3,5-trimethoxybenzene.chemrox - 1-11-2007 at 19:05
woops, yes you're so right. CO2 was mentioned!
Now I have it .. just like the Grignard using CO2..
thanks to Nicodem and Sauron (U2U)
CRX
PS- I just got a book I'm excited about : The Art of Writing Reasonable Reaction Mechanisms by Grossman, UKY, 2002.
