08-26-04 18:09
No 527516
The aim is to activate(acidification) the benzylic C which is then deprotonated with a strong base such as NaOEt and reacted with ethyl acetate (claisen condensation?) to afford 1-OAc-p-2-p s
Could these theories be true or am I flyin too high :)
reacting benzyl alcohol wih acetyl chloride or ac2o will produce acetyl ester of1 the alcohol. If the benzylic C is acidic enough (active methylene) reacting this ester with ethyl acetate in the presence of sodium ethoxide will produce 1-O-acetyl-1-phenyl-2-propanone (this naming is probably wrong I mean the acetyl ester of 1-OH-1-phenyl-2-propanone)
hydrolysis will afford 1-OH-P-2-P
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(Newbee)
08-26-04 18:16
No 527518
oops I understood that under these basic conditions the acetyl group will come off before the benzylic hydrogen.
But what if other groups used like nitrate or phosphate esters which bond strong enough to survive the NaOEt?
(Newbee)
08-27-04 07:21
No 527709
make it an ether instead of ester?
Claisen condensation. The usual method is to use benzyl cyanide with ethyl acetate. Perhaps as you suggest, a simple ester or ether could be sufficient.
It's good to bee back! Don't trust your computer!!
(Newbee)
08-27-04 17:01
No 527790
I dont think that an etherification would activate the benzylic C and its hard to make an ether from the Benzyl alcohol (You must chlorinate the OH with HCl then react it with sodium alkoxide )
In a Ph-C-CN structure the benzylic carbon is donated with electrons both by the phenyl ring and CN group. Therefore it can be deprotonaed with sodiumethoxide tnen reacted w ethyl acetate in a claisen condensation. (In other words the enolate of the ethyl acetate (w/sodium ethoxide) is hydrolyzed by the acidic benzylic C to form the a-phenylacetonitrile.)
This is simple. But I want something that will form an ester with benzyl alcohol donate it with electrons and bond strong enough that it wont be torn off by the NaEthoxide while activating the benzylic carbon so that it will be deprotonated by the base
are these possible?
(Hive Bee)
08-27-04 18:02
No 527797
In a Ph-C-CN structure the benzylic carbon is donated with electrons both by the phenyl ring and CN group.
The -CN and (much less) the -Ph group withdraw electron density. They don't donate electrons. That's why the benzylic carboanion becomes more stable by distributing the anion charge in various possible resonance structures. Therefore, what you want is an highly electrophylic group on the benzylic or o/p-aromatic position. Electron withdrawing groups are -NR4+, -NO2, -CO-R, -CN, -COOR, -SO2-R, halogens... but only a few are useful, notably those which have a stronger mesomeric than inductive effect and those which are not to electrophylic per se (read the thread Post 490390 (politoxicomania: "P2P-derivate related", Methods Discourse) for more on this). Therefore your choice reduces to only a few: -NO2, -CN, -SO2R.
I want something that will form an ester with benzyl alcohol (...) that it wont be torn off by the NaEthoxide while activating the benzylic carbon so that it will be deprotonated by the base
Some esters can withdraw electrons trough the inductive efects (halogenides and pseudohalogenides) but they don't have any mesomeric effect and are therefore useless since they react with nucleophylic bases only as electrophyls (except for the Darzen's reaction, but there you also have the -COOR in addition to the halogen).
“The real drug-problem is that we need more and better drugs.” – J. Ott
(Newbee)
08-28-04 02:33
No 527849
Ooops thanks for the correction englis is not my native language therefore these errors infrequently occur
So would the nitro ester of benzyl alcohol withdraw the electrons powerful enough to loosen the benzylic carbon's hydrogens?
And can the alcohol be tosylated? What can the tosyl ester be used for?
Im cofused between these active methylene cmpounds, esters, sodium alkolates, tosylates and I really even cant decide what to ask so please forgive the confusing questions
all help would be appreciated
(Hive Bee)
08-28-04 08:06
No 527918
So would the nitro ester of benzyl alcohol withdraw the electrons powerful enough to loosen the benzylic carbon's hydrogens?
No! A "nitro ester" is -O-NO2 which is nearly not the same as the nitro group -NO2 where the nitrogen is connected directly to a carbon atom. It is because of the oxygen atom in between that a nitrate has only an inductive effect while the nitro has a good mesomeric effect and so can form stabilising resonance structure for the carboanion.
And can the alcohol be tosylated? What can the tosyl ester be used for?
Off course it can be tosylated just like any alcohol. Benzyl tosylate is a powerful electrophyle that can be used to benzylate various nucleophyles in the same manner like benzylchloride or benzylbromide (though these two are much more practical).
Im cofused between these active methylene cmpounds, esters, sodium alkolates, tosylates and I really even cant decide what to ask so please forgive the confusing questions
The least you could do is take a general organic chem book in the library and study the basics. These things are described in just any general chem book and you should understand these concepts anyway if you plan a new reaction.
“The real drug-problem is that we need more and better drugs.” – J. Ott