From: by way of Joao Aires de
Sousa (r.ragno$##$caspur.it)
Date: Wed Mar 19 1997 - 03:38:58 EST
On Tue, 18 Mar 1997, Mark Rosen wrote:
> At 08:50 AM 3/18/97 +0100, you wrote:
> >Dear colleagues,
> >I've synthesized many 6-substituted-2-alkylthio-4-oxo-pyrimidines by
> >S-alkylation of 2-thiouracils with alkyl halides and potassium carbonate
> >in DMF, but when I tried to introduce the cyclopropyl group in the same
> >way (i.e. with cyclopropyl iodide) I failed. Do you have any suggestion?
> >I'll summarize to the list the answers I'll get.
> >Thank you in advance,
> >
> >Gianluca " Blue Merlin" Sbardella
> >
>
> I would imagine this is due to the fact that the sulfur nucleophile
> displaces the halogen in an SN2 type mechanism. Thus the sulfur
> approaches the from the opposite side of the halide. This is precluded
> in the cyclopropyl system. Furthermore, SN2 type reactions occur with
> inversion of stereochemistry (if relevent), showing that the relative
> position of the substituants at the carbon in question must invert. This
> again cannot occur in a cyclic system.
>
>
Dear Mark,
thank you for your answer.
As regards to cyclic systems, the reaction was succesful with cyclohexyl
iodide as well as cyclopentyl iodide. I believe that the peculiar
structure of cyclopropyl ring (banana-like orbitals...) prevents the
nucleophile to approach sufficiently. Any other suggestions?
Thank you again,
Gianluca "Blue Merlin" Sbardella
***************************************************************
* *
* Dr. Gianluca Sbardella E-mail: r.ragno$##$caspur.it *
* Dip. Studi Farmaceutici *
* Universita' "La Sapienza" Phone: 39-6-49913814 *
* P.le A. Moro, 5 Fax: 39-6-491491 *
* 00185 Roma *
* ITALY *
* *
* *
* "Il destino e' quel che e', non c'e' scampo piu' per me.." *
* (Gene Wilder, "Frankenstein Junior") *
* *
* "Destiny, destiny, no escaping that for me..." *
* (Gene Wilder, "Young Frankenstein") *
* *
***************************************************************
__________________
ORGLIST - Organic Chemistry Mailing List.
WWW Homepage: http://www.dq.fct.unl.pt/orglist/
To post a message (TO EVERYBODY) send to orglist$##$dq.fct.unl.pt
To unsubscribe, send to listserver$##$dq.fct.unl.pt the message:
unsubscribe orglist.
List coordinator: Joao Aires de Sousa (jas$##$mail.fct.unl.pt)
This archive was generated by hypermail 2.1.4 : Fri Sep 19 2003 - 12:14:31 EDT