S. Ghelli et al., Structures and reactivities of 1-oxo-cycloalkan-2-ylideneacetic acids. A H-1 NMR, modelling and photochemical study, TETRAHEDRON, 56(38), 2000, pp. 7561-7571
Four 1-oxo-cycloalkan-2-ylideneacetic acids, differing in the size of the a
liphatic ring and in the nature of the condensed unsaturated cycle, exhibit
different reactivities towards hydrazine, leading in only one case to the
desired tryciclic pyridazinone. The observed differences in behaviour canno
t be ascribed to different configurations at the exocyclic double bond of t
he four acids: H-1 NMR experiments, combined with UV photolysis, have shown
that all compounds have been prepared in the E form and are stable in the
absence of light and catalysts. The photochemically obtained Z isomers show
an increasing tendency to form tricyclic lactones with increasing size of
the aliphatic ring. A theoretical structural analysis of the E and Z isomer
s, the tricyclic lactones and some of the hypothetical intermediates of the
reaction with hydrazine suggests the size of the aliphatic ring and the as
sociated flexibility to be crucial in modulating the ability of these compo
unds to form tricyclic products. (C) 2000 Elsevier Science Ltd. All rights
reserved.