Exploiting predisposition in the stereoselective synthesis of mono-, bi- and tetracyclic oxygen heterocycles: equilibration between, and trapping of, alternative di- and tetraacetals.
The desymmetrisation of 1,4-difuran-2-ylbutane-1,4-diol by Sharpless asymmetric oxidation gave the corresponding desymmetrised product in > 96% ee. However, the product existed as a mixture of two interconverting isomers, both of which were mixtures of anomers. The product could be trapped in high yield with a range of reagents to give stable adducts with embedded pyran-3-one, 1,6-dioxaspiro[4.5]decane or pyrano[3,2-b]pyran ring systems. The strategy was also applied in the interconversion between alternative tetracycles and, under acidic conditions, this process was thermodynamically controlled. The selectivity of the process was rationalised by molecular modelling using the HF/6-31G* parameter set.
Bartlett
Stephen
S
Department of Chemistry, University of Leeds, Leeds, UK LS2 9JT.
Hodgson
Robert
R
Holland
Joanne M
JM
Jones
Matthew
M
Kilner
Colin
C
Nelson
Adam
A
Warriner
Stuart
S