A. Arduini et al., DIRECT REGIOSELECTIVE FORMYLATION OF TETRAALKOXYCALIX[4]ARENES FIXED IN THE CONE CONFORMATION AND SYNTHESIS OF NEW CAVITANDS, Journal of organic chemistry, 60(5), 1995, pp. 1448-1453
Regioselectivity of the formylation of tetraalkoxycalix[4]arene fixed
in the cone conformation has been studied. Direct, diametrical (1,3) d
iformylation of calix[4]arenes having four chelating chains at the low
er rim has been achieved. Simple tetraalkoxycalix[4]arenes produce a m
ixture of diametrical (1,3) and proximal (1,2) diformylated products.
The (1,3) functionalized compounds have been used for the synthesis of
double calix[4]arenes 12a,d linked via the upper rim. The residual mo
bility of these cone conformers is indicated by the X-ray crystal stru
cture of compound 12d, which shows a flattened cone conformation, and
by the reactive behavior of 1,3-bis(hydroxymethyl) derivatives 9a,d wh
ich give very distorted 1,3-bridged compounds 11a,d, through an intram
olecular cyclization process.