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

56 NITRILE OXIDES
Ar
R 1 N
174
N O
O
RSO2N
O
O N
175
Reactions of stable mesito- and duronitrile oxides with 1-chloroalkyl isocyanates
R 1 R 2 CClNCO (R 1 = CF3, R 2 = Ph, 4-MeC6H4; R 1 = CCl3, R 2 = H)
gave oxadiazolones 176. The double adducts are formed by the cycloaddition
of one nitrile oxide molecule at the isocyanate C=N bond and the nucleophilic
addition of the chloroalkyl moiety to a second nitrile oxide molecule (344).
R
Cl
C
R
NOCR 1 R 2 N
176
Cycloaddition of aromatic nitrile oxides, RCNO (R = 2,4,6-Me3C6H2, 2,3,5,6-
Me4C6H, 3,5-Cl2-2,4,6-Me3C6) to isocyanatophosphoric dichloride occurs at both
the C=N and C=O bond of the isocyanato group to afford an inseparable mixture
of heterocyclic products, consisting of 3-aryl-4-dichlorophosphinoyl-4,5-dihydro-
1,2,4-oxadiazol-5-ones 177 (X = P(O)Cl2) and 5-aryl-2-dichlorophosphinoylimino-2H
-1,3,4-dioxazoles 178. The structure of these compounds was conÞrmed
by spectral data and chemical transformations, in particular, by hydrolysis of
177 (R = 2,4,6-Me3C6H2, X= P(O)Cl2) togive177 (X = H) (345). Reactions
of methyl trißuoropyruvate and its (methoxycarbonyl)imine CF3C(:X)CO2Me
(I; X = O, NCO2Me) with aromatic nitrile oxides RCNO (R = mesityl, duryl)
gave dioxazoles and oxadiazoles 179 (346).
R X R
F3C CO2Me N
O
O X
N
O
O
N
O
N P(O)Cl2 N
R
177 178 179 (X = O, NCO2Et)
1.3.4.2.5. Carbonyl and Thiocarbonyl Compounds α-(Hydroxyimino)phenylacetonitrile
oxide (generated in situ at room temperature from PhC(:NOH)C
(:NOH)Cl in the presence of NaHCO3 or Et3N) reacts with simple aldehydes and
ketones R 1 R 2 CO to give 1,4,2-dioxazoles 180 (347). Related dioxazoles, formed
by cycloaddition of benzonitrile oxide to aromatic aldehydes, upon treatment
with t-BuOK, undergo cyclo-reversion, allowing direct conversion to substituted
benzoic acids or their esters (348).
N
O
O
Ar