Nitrile Oxides, Nitrones, and Nitronates in Organic Synthesis : Novel ...

APPLICATIONS OF NITRILE OXIDES 107
Several 4-(3-alkyl-2-isoxazolin-5-yl)phenol derivatives that possess liquid
crystal properties have also been obtained (533–535). In particular, target compounds
such as 463 (R = pentyl, nonyl) have been prepared by the reaction of
4-acetoxystyrene with the nitrile oxide derived from hexanal oxime, followed by
alkaline hydrolysis of the acetate and esteriÞcation (535). A homologous series of
3-[4-alkyloxyphenyl]-5-[3,4-methylenedioxybenzyl]-2-isoxazolines, having chiral
properties has been synthesized by the reaction of nitrile oxides, from the
dehydrogenation of 4-alkyloxybenzaldoximes. These compounds exhibit
cholesteric phase or chiral nematic phase (N*), smectic A (SA), and chiral smectic
phases (SC*), some at or just above room temperature (536).
Liquid-crystalline 3,4-disubstituted furoxans such as 464 (R = 4-alkoxybenzoyl,
Ph) have been prepared by cyclodimerization of 4-AcOC6H4CNO, followed
by hydrolysis to 464 (R = H) and acylation. The products form a nematic
mesophase (537).
OR
N
O
464
NO
Many papers and patents are devoted to the use of nitrile oxides for the
preparation of fullerene derivatives with practically attractive properties.
Electroactive 3-(N-phenylpyrazolyl)fullereno[1,2-d]isoxazolines have been
synthesized by using 1,3-dipolar cycloaddition of pyrazole nitrile oxides, generated
in situ, toC60 at elevated temperature or microwave irradiation. The cyclic
voltammetry measurements show a strong donor pyrazole ring, and a better acceptor
ability of the fullerene moiety than the parent C60 (538). Treating fullerene C60
with mesitonitrile oxide in toluene gives fullerene–nitrile oxide adduct, which is
supposed to be useful for electrical and optical components (539).
The methodology required for the construction of fullerene-based nanostructures
including fullerenes and rigid spacers has been investigated. Such
assemblies require the ability to control the regiochemistry of multiple addition
of fullerenes. The kinetic and thermodynamic isomer distribution of nitrile
oxide dipolar additions to C60, as well as the separation and characterization of
the major species have been reported (540, 541). The structures of such fullerene
isoxazolines, as nano-scale connectors, have been optimized by using the semiempirical
PM3 calculations. Also the regiochemistry of the second addition of a
nitrile oxide to a fullerene isoxazoline has been considered. The results indicate
that fullerene isoxazoline derivatives are useful nano-scale connectors with the
possibility of attaching spacer units in a speciÞc angular arrangement (542, 543).
Novel C60 and C70 adducts have been synthesized by [2 + 3] cycloadditions of
the appropriate nitrile oxides. Variations in the distance and geometry of the donor
OR