ORGLIST: Re: Everybody Digest, Vol 13, Issue 11 ; 3. witig reaction (saraswati velu)

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From: Lakshmipathi Pandarinathan (plpathi$##$hotmail.com)
Date: Wed Oct 19 2005 - 15:53:17 EDT


Velu
You must remember that the polar spot is phosphine oxide or/ and
3,5-dihydroxy benzaldehyde (deprotected due to very strong basic
conditions). One carbon homologation by phosphorane gives better yields when
you use phosphonium bromide rather than iodide. However, when you use
iodide, you could still get good yields if you may follow the rules such as
(1) use 4 or more equivalents of wittig salt and 2 equivalents of base (2)
butoxide is good enough, but add this to the suspension of wittig salt in
anhydrous THF. Reverse addition might give reduced yields (3) quench the
reaction with sat NH4Cl and follow usual work up procedure (4) you could
remove most of the phospine oxide (large amounts formed as by product) by
leaching the crude residue with diisopropyl ether. Diisopropyl ether
dissolves most of the product and very less of phosphine oxide.
Pathi


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Subject: Everybody Digest, Vol 13, Issue 11


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> Today's Topics:
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> 1. a ques on 3-methyl isoxazolone (guduru venkat reddy)
> 2. HPLC of human salivary protein (N.V. Anil Kumar)
> 3. witig reaction (saraswati velu)
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> Message: 1
> Date: Tue, 18 Oct 2005 08:49:35 +0530
> From: "guduru venkat reddy" <vrguduru$##$hotmail.com>
> Subject: ORGLIST: a ques on 3-methyl isoxazolone
> To: everybody$##$orglist.net
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> Hi friends,
> could anybody plz disclose the synthetic procedure for 3-methyl
> isoxazolone,
> Thank you,
> reddy
>
> Venkat Reddy Guduru
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> Date: Tue, 18 Oct 2005 13:08:16 +0100 (BST)
> From: "N.V. Anil Kumar" <nvanil$##$yahoo.com>
> Subject: ORGLIST: HPLC of human salivary protein
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> Hello all,
>
>
>
> I would like to know is there any reference for the estimation of Human
> salivary protein based on HPLC. If so, kindly send me personally about the
> original aritcle or reference
>
>
>
> Looking forward to get positive reply
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> With warm regards
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> Anil
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> (nvanil$##$yahoo.com)
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> Message: 3
> Date: Tue, 18 Oct 2005 03:28:18 -0700 (PDT)
> From: saraswati velu <saraswativ$##$yahoo.com>
> Subject: ORGLIST: witig reaction
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> Hello,
>
> Does anyone know how to increase the yield of witig reaction for 3,5
> protected dihydroxy with TBS- benzaldehyde. I only manage to get about 40%
> yield using potassium tert-butoxide, THF and methyltriphenylphosphonium
> iodide. From the TLC, almost all the starting material have been consumed
> and left with 2 products which are the functionalised styrene and a polar
> product which might be the phosphonium salt I guess.
> Pls help.
> Thanks,
> Saras
>
>
>
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