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

REACTIONS OF NITRILE OXIDES 37
these reactions showed that closed [5,6] and open [6,6] additions are not probable
and that closed [6,6] addition is the most favored one (258).
1.3.4.1.6. Heterocycles Both non-aromatic unsaturated heterocycles and heteroaromatic
compounds are able to play the role of ethene dipolarophiles in reactions
with nitrile oxides. 1,3-Dipolar cycloadditions of various unsaturated oxygen
heterocycles are well documented. Thus, 2-furonitrile oxide and its 5-substituted
derivatives give isoxazoline adducts, for example, 90, with 2,3- and 2,5-dihydrofuran,
2,3-dihydropyran, 1,3-dioxep-5-ene, its 2-methyl- and 2-phenyl-substituted
derivatives, 5,6-bis(methoxycarbonyl)-7-oxabicyclo[2.2.1]hept-2-ene, and 1,4epoxy-1,4-dihydronaphthalene.
Regio- and endo-exo stereoselectivities have also
been determined (259).
O O N
90 (R = H, NO2, 4-, 3-nitrophenyl)
1,3-Dipolar cycloaddition reactions of 2,6-dichlorobenzonitrile oxide with
2 ′ ,3 ′ -didehydro-2 ′ ,3 ′ -dideoxythymidine 91 (R = H, Me3CMe2Si), at its 2,5dihydrofuran
double bond, gave nucleosides 92 and 93 in 67% yield and 3:2
ratio and 96% yield and 3:1 ratio, respectively (260).
RO
Me
O
O
N
NH
O
RO
O
R
O N R 1
RO
R 1
91 92 93
1,3-Dipolar cycloadditions of benzonitrile oxide, its substituted derivatives
as well as 9-anthro- and 2-furonitrile oxides to 5-alkoxy- and 5-hydroxy-2(5H )furanones
afforded regiospeciÞcally furoisoxazoles 94. 5-Methoxy- and 5-ethoxyfuranones
gave exclusively exo-94, whereas 5-hydroxyfuranone gave a 52:48
mixture of exo-94 (R = Ph, R ′ = H) and its endo diastereomer (261). Reaction
of benzonitrile oxide with 5-(R)-(1-menthyloxy)-2(5H )-furanone proceeds
regioselectively to give (3aS ,6R,6aR)-3a,6a-dihydro-4-[(1R,2S ,5R)-5-methyl-2-
(1-methylethyl)cyclohexyloxy]-3-phenylfuro[3,4-d]isoxazol-4(3aH )-one and its
regioisomer, (3aR,4R,6aS )-3a,6a-dihydro-4-[(1R,2S ,5R)-5-methyl-2-(1-methylethyl)cyclohexyloxy]-3-phenylfuro[3,4-d]isoxazol-6(4H
)-one, in a 68:32 ratio
(262).
O
N
O