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Suzuki reaction and silyl protection



  1. #1
    arom68

    Unhappy Suzuki reaction and silyl protection

    I've been trying to carry a Suzuki rxn out on an aryl bromide and a tbutyldiphenylsilyl- protected phenyl boronic acid but I have read ( Tetrahedron Utters, Vol. 38, No. 2, pp. 187-190, 1997) that the protecting group would not survive alkalinity of the reaction. The protection on phenolic OH is absolutely necessary and it must also get deprotected afer the Suzuki coupling easily. TBDPS and TOM look auspicious for the deprotection step but I first need to get away with their base sensitivity. Any suggestions?

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  3. #2
    Fajan

    Re : Suzuki reaction and silyl protection

    tButyl Ester?

  4. #3
    HarleyApril

    Re : Suzuki reaction and silyl protection

    Hi
    I suppose Fajan means a pivaloyl ester
    Benzyl ether could be an alternative choice
    Additionnal substitutions with methoxy groups allows additionnal methods of deprotection

    Le site étant plutôt francophone, la question est de savoir quel groupe protecteur on peut utiliser qui résisterait aux conditions basiques d'une réaction de Suzuki, les silylés ne seraient pas un bon choix selon la référence citée
    cordialement
    Dernière modification par HarleyApril ; 29/03/2009 à 13h54.

  5. #4
    shaddock91

    Re : Suzuki reaction and silyl protection

    Bonjour.

    Es-tu sûr que la protection du phenol est vraiment nécessaire ? J'ai déjà vu des réactions de Suzuki marcher sur des composés du type HO-Ar-B(OR)2 sans protection de la fonction phenol. Reaction classique dans H2O/EtOH ou toluène/Cs2CO3.

  6. #5
    arom68

    Re : Suzuki reaction and silyl protection

    Hiya all,
    Well, I might have forgotten to add that the protecting group also needed to be removed EASILY. I tried benzyl but Pd/H2 deprotecting just gives me mess. The reaction is carried out in such a small schale that digging deproted product, if any, was unsussesful.
    So the question still remains the same: what protecting group should be used that is:1- compatible with Suzuki reaction and 2- easily comes off afterwards

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  8. #6
    pitt the chemist

    Re : Suzuki reaction and silyl protection

    hi
    the TBDPS on a phenol might survive to Suzuki conditons. But, you dont really need to protect the it to carry the reaction out. As HarleyApril said the benzyl would be a good alternative if you've got a H2-reactor which will give you a very clean product afterward
    bye
    Dernière modification par pitt the chemist ; 28/03/2009 à 19h02.

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  10. #7
    arom68

    Re : Suzuki reaction and silyl protection

    I know it, but I need it protected for the rest of the synthesis.
    thks btw

  11. #8
    shaddock91

    Re : Suzuki reaction and silyl protection

    Citation Envoyé par arom68 Voir le message
    Hiya all,
    Well, I might have forgotten to add that the protecting group also needed to be removed EASILY. I tried benzyl but Pd/H2 deprotecting just gives me mess. The reaction is carried out in such a small schale that digging deproted product, if any, was unsussesful.
    So the question still remains the same: what protecting group should be used that is:1- compatible with Suzuki reaction and 2- easily comes off afterwards
    You have to protect the OH group (I think it's not necessary). However, you can use the 4-MeOBenzyl protective group which is acid sensitive, for the deprotection (no catalytic hydrogenation ---> no mess ?).

  12. #9
    arom68

    Angry Re : Suzuki reaction and silyl protection

    Citation Envoyé par shaddock Voir le message
    You have to protect the OH group (I think it's not necessary). However, you can use the 4-MeOBenzyl protective group which is acid sensitive, for the deprotection (no catalytic hydrogenation ---> no mess ?).
    I KNOW OH protecting is not necessary for Suzuki ITSELF but I NEED IT FOR THE REST OF MY TOTAL SYNTHESIS.
    Acid is also a big no no for me. I have acid hydrolysis problem in my structure

  13. #10
    shaddock91

    Re : Suzuki reaction and silyl protection

    2-nitro benzyl group could be remove by photolysis, is it possible to use that way with your structure?

  14. #11
    arom68

    Re : Suzuki reaction and silyl protection

    Citation Envoyé par shaddock Voir le message
    2-nitro benzyl group could be remove by photolysis, is it possible to use that way with your structure?
    huuum, photolysis doesn't look bad. I gotta look it up.
    thnks

  15. #12
    HarleyApril

    Re : Suzuki reaction and silyl protection

    résumé des épisodes précédents

    arom à besoin d'un groupe protecteur de son phénol pour la suite de sa synthèse, il faut que le groupe tienne aux conditions de Suzuki
    le benzyle et l'hydrogénation n'ont pas donné de bons résultats
    un para-méthoxybenzyle ne convient pas car la molécule ne tiendrait pas aux conditions trop acides
    shaddock propose donc un ortho-nitrobenzyl qui s'en va par photolyse
    Dernière modification par HarleyApril ; 29/03/2009 à 13h57.

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  17. #13
    HarleyApril

    Re : Suzuki reaction and silyl protection

    we have also recently tried allyl with a deprotection by Pd(PPh3)4 and sodium borohydride

    if compatible with the rest of your molecule !

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