From: Emil Fischer (RB.Woodward$##$gmx.net)
Date: Wed Jun 18 2003 - 16:15:56 EDT
Dave, dear everybody
thanks for your hints; do you have an idea for cleaving N-Benzyl-protected
5-MeO-indolones? Birch is due to the MeO-Phe moiety no option; H2 (up to 7bar)
over Pd/C or Pd(OH)2 in EtOH +/- HOAc gave no conversion. Do you know good
hydrogenolysis conditions for this transformation? Do you have experiences
with LDBB to cleave Lactam-N-Benzyl groups?
Thanks for any answer
Emil
> It seems to be my day for answering questions.
>
> Cyclodextrins: If you are using the heptakis(manno-epoxy)-
> cyclodextrin and a nucleophile of any appreciable size, the cavity
> becomes blocked by the incoming group.
>
> Frequently the initial trans-diaxial (altro)-product inverts the
> conformation from 4C1 to 1C4, placing the C2 and C3 substituents
> equatorial. Smaller nucleophiles work, like ammonia, azide or hydride
> see our paper.
>
> Synthesis of the first per(3-deoxy)-cyclo-oligosaccharide:
> hepta(manno-3-deoxy-6-O-t-butyldimethylsilyl)-beta-cyclodextrin, D. R.
> Kelly and A. K. Mish'al, Tetrahedron: Asymmetry, 1999, 10, 3627-3648
> (ISSN 0957-4166).
>
> We are looking at the use of more substantial nucleophiles
>
> N-Benzyl cleavage. This is best done with PtO2 under slightly acidic
> conditions. Amidic benzyls are 100% stable under these conditions.
> The opposite selectivity (amide benzyl before non-amidic benzyl) can
> be achieved with sodium in liquid ammonia. Our experience is with
> bis-N-benzyl-piperidinones.
>
> Micro/small scale hydrogenation.
> Use a balloon for quick facile hydrogenations. This should be
> atttached to a two way tap, so that the other way can be used to
> evacuate the flask by vaccum. We use a double oblique two way tap,
> attached to a ground glass joint. Bind the balloon to a couple of cm of
> rubber tubing for easy filling.
>
> Cheers
>
> Dave Kelly
>
> Dr David R. Kelly
> Dept. of Chemistry, Cardiff University, PO Box 912, Cardiff, CF10
> 3TB, UK
> Phone 02920-874063: Fax 02920-874030
> Mobile 07971-240448: Home 02920-610891
> Web page http://www.cf.ac.uk/uwc/chemy/staff/kelly.html
> For the "Elephants and Butterflies" article see
> http://www.semiochemica.org.uk/articles/articlesidx.html
> BEST Record: http://expertise.cos.com/cgi-bin/exp.cgi?id=498275
> For catalysis see http://www.chemsoc.org/cgi-
> shell/events/nforedisp.pl?ID=551
> Cardiff University is the public name of the University of Wales,
> Cardiff, a constituent institution of the
> University of Wales.
>
>
> _______________________________________________
> ORGLIST - Organic Chemistry Mailing List
> Website / Archive / FAQ: http://www.orglist.net
> To post a message (TO EVERYBODY) send to everybody$##$orglist.net
> To unsubscribe, send to everybody-request$##$orglist.net the message:
> unsubscribe your_orglist_password your_address
> List coordinator: Joao Aires de Sousa (coordinator$##$orglist.net)
>
-- +++ GMX - Mail, Messaging & more http://www.gmx.net +++ Bitte lächeln! Fotogalerie online mit GMX ohne eigene Homepage!_______________________________________________ ORGLIST - Organic Chemistry Mailing List Website / Archive / FAQ: http://www.orglist.net To post a message (TO EVERYBODY) send to everybody$##$orglist.net To unsubscribe, send to everybody-request$##$orglist.net the message: unsubscribe your_orglist_password your_address List coordinator: Joao Aires de Sousa (coordinator$##$orglist.net)
This archive was generated by hypermail 2.1.4 : Fri Sep 19 2003 - 12:17:26 EDT