Formation and X-ray structural study of enantiopure fused 1,5-oxathiocane derivatives
Abstract
The reaction of
(E,RS)-3-[(1S)-isoborneol-10-sulf
inyl]-1-methoxybuta-1,3-diene
1 with
benzaldehyde or p-nitrobenzaldehyde, when carried out in
dichloromethane in the presence of trimethylsilyl
trifluoromethanesulfonate, leads mainly to enantiopure condensed
2-aryl-4-ethylidene-1,5-oxathiocane S-oxides. The reaction path
begins with the ionic addition of the enantiopure diene 1 onto the
C![[double bond, length as m-dash]](https://www.rsc.org/images/entities/char_e001.gif)
O group activated by trimethylsilyl cation attack on the
carbonyl oxygen. The almost complete diastereoselection observed in the
following closure of the eight-membered ring is interpreted as being a
consequence of the conformational control on cyclization which leads to
the thermodynamically favoured isomer. The crystal structure of the
2,4-dinitrophenylhydrazone of the α,β-unsaturated aldehyde 5,
obtained by reacting diene 1 with p-nitrobenzaldeyde, supports
the stereochemical results.
1 with
benzaldehyde or p-nitrobenzaldehyde, when carried out in
dichloromethane in the presence of trimethylsilyl
trifluoromethanesulfonate, leads mainly to enantiopure condensed
2-aryl-4-ethylidene-1,5-oxathiocane S-oxides. The reaction path
begins with the ionic addition of the enantiopure diene 1 onto the
CO group activated by trimethylsilyl cation attack on the
carbonyl oxygen. The almost complete diastereoselection observed in the
following closure of the eight-membered ring is interpreted as being a
consequence of the conformational control on cyclization which leads to
the thermodynamically favoured isomer. The crystal structure of the
2,4-dinitrophenylhydrazone of the α,β-unsaturated aldehyde 5,
obtained by reacting diene 1 with p-nitrobenzaldeyde, supports
the stereochemical results.
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