From: David Kelly (KellyDR$##$Cardiff.ac.uk)
Date: Tue Jun 17 2003 - 16:18:54 EDT
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.
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