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

38 NITRILE OXIDES
O
O
OR′ H
H
94
1,3-Dipolar cycloaddition of 2,4-(trimethylsilyl)- and 2,4-(trimethylgermyl)substituted
thiophene-1,1-dioxides as well as silylated 2,2 ′ -bithiophene-1,1dioxides
was investigated. It was shown that only the C(4)=C(5) double bond
of 2,4-disubstituted thiophene-1,1-dioxides interacts with acetonitrile oxide to
give thienoisoxazoline dioxides. Bithiophene derivatives were inactive or their
reaction with nitrile oxide was accompanied by desilylation. Cycloaddition of
benzonitrile oxide with all mentioned sulfones did not occur. The molecular structure
of 3a-methyl-5,6a-bis(trimethylgermyl)-3a,6a-dihydrothieno[2,3-d]isoxazole
4,4-dioxide was established by X-ray diffraction (263) .
N-Arylmaleimides are useful reagents for trapping and characterization of
nitrile oxides (see, e.g., Ref. 165). However, their cycloadducts can also be target
products. Thus, a series of 3,5-diaryl-4,6-dioxo-3a,4,6,6a-tetrahydropyrrolo-
[3,4-d]isoxazoles 95 was obtained by 1,3-dipolar cycloaddition of substituted
benzonitrile oxides with N-(2,6-dialkylphenyl)maleimides. Certain compounds
95 showed bactericidal and fungicidal activity (264).
R O
R 1
N
O
95
O
N
R
O N
R = R 1 = Me, Et; R = Me, R 1 = Et;
R 2 = Ph, 2-MeOC 6H 4, 4-MeOC 6H 4, 4-ClC 6H 4, 2,4-Cl 2C 6H 3, 3-O 2NC 6H 4,
4-O 2NC6H4, 4-FC6H4, 4-MeC6H4, 2-ClC6H4, 3,4-Cl2C6H3, 3,4-(OCH2O)C6H3,
3-MeOC6H4, 3,5,2-Cl2(MeO)C6H2, 3,4,5-(MeO)3C6H2
4-[Chloro(hydroxyimino)methyl]-3-phenyl-1,2,3-oxadiazolium-5-olate-(3phenylsydnone-4-carbohydroximoyl
chloride) reacts in situ (through nitrile oxide)
with N-arylmaleimides or 2-methyl-N-phenylmaleimide to give 5-aryl-3-(3phenylsydnon-4-yl)-3a,6a-dihydropyrrolo[3,4-d]isoxazole-4,6-diones
or 6amethyl-5-phenyl-3-(3-phenylsydnon-4-yl)-3a,6a-dihydropyrrolo[3,4-d]isoxazole-
4,6-diones, respectively (265).
The cycloaddition of prop-1-ene-1,3-sultone to a variety of nitrile oxides (generated
from corresponding α-chlorobenzaldoximes and used in situ) afforded
R 2