Is it possible to convert Alkoxide to tosylate directly?

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Jason Smith - 20 Oct 2003 16:59 GMT

Need help:

J. of Labelled Compounds and Radiopharmaceuticals(34(4), 383-90;
1994) reported a method for preparation HOCH2CH2OH (Carbon 11 labeled)
from KCN (C11) in three steps
Step 1: KCN + ClCH2OC(O)C(CH3)3 ----> CNCH2OC(O)C(CH3)3
Step 2: CNCH2OC(O)C(CH3)3 +HCl +EtOH ---> HOCH2CO2Et
Step 3: HOCH2CO2Et + LiAlH4 ----> HOCH2CH2OH

Now I need to prepare labeled TsOCH2CH2OTs. However workup in step 3
is a tedious process since it is quite difficult to seperate
HOCH2CH2OH from water and Al(OH)3. My question is: can I add pTsCl to
the step 3 raction mixture to make TsOCH2CH2OTs directly from
-Al-OCH2CH2O-Al-? Do anyone has such experience or know some
reference about it?

Thanks

Jason

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Paul J. Franklin(moderator - sci.chem.organic.synthesis)
http://organicworldwide.net/sci.chem.organic.synthesis
Georgia State University <chepjf@panther.gsu.edu>
Atlanta, GA

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Steven - 22 Oct 2003 14:24 GMT

> Need help:

> J. of Labelled Compounds and Radiopharmaceuticals(34(4), 383-90;
> 1994) reported a method for preparation HOCH2CH2OH (Carbon 11 labeled)
> from KCN (C11) in three steps
> Step 1: KCN + ClCH2OC(O)C(CH3)3 ----> CNCH2OC(O)C(CH3)3
> Step 2: CNCH2OC(O)C(CH3)3 +HCl +EtOH ---> HOCH2CO2Et
> Step 3: HOCH2CO2Et + LiAlH4 ----> HOCH2CH2OH

> Now I need to prepare labeled TsOCH2CH2OTs. However workup in step 3
> is a tedious process since it is quite difficult to seperate
> HOCH2CH2OH from water and Al(OH)3. My question is: can I add pTsCl to
> the step 3 raction mixture to make TsOCH2CH2OTs directly from
> -Al-OCH2CH2O-Al-? Do anyone has such experience or know some
> reference about it?

> Thanks

> Jason

That´s a good idea, but you will not have any success, because the
Al-Oxygen bound is far too strong as being broken by attack with
TosCl. Also, if you will add TosCl to the "reduction soup", there will
occur the following problem: The sulfonyl group will be reduced to
sulfide group with a "good smell" due to the excess of the hydride
which is always needed for complete reaction. What you should do is,
simply add water (carefully) to quench the reaction, remove the
precipitated salts, and add TosCl to the filtrate. The yield will be
poor, since it will be a great problem to remove the ethylene glycol
from the Al(OH) salts, due to the high polarity of the glycol, which
is absorbed and bound physically to the polar Al- salts.

Signature

Paul J. Franklin(moderator - sci.chem.organic.synthesis)
http://organicworldwide.net/sci.chem.organic.synthesis
Georgia State University <chepjf@panther.gsu.edu>
Atlanta, GA

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Natural Science Forum / Chemistry / Organic Synthesis / October 2003

Is it possible to convert Alkoxide to tosylate directly?