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

86 NITRILE OXIDES
PhSO 2
R
R′C=NOH,
NaOCl
CH 2Cl 2
R = H, Me; R′ = Ph, 2-pyridyl
Scheme 1.48
PhSO 2
R
O
H
N
O
R
N
CNCH 2 CO 2 Et,
NaH
402
OEt
R′
O N
of metal salts to be reduced and thereby makes the reaction industrially applicable.
In particular, a mixture (86:14) of diastereomers 403 and 404 (Ar = Ph) was
prepared in 71% yield.
Ar
N
O
Ph
N O
Ar
O
O
O
403 404
Ph
N
O
N
O
Ph
O
O
O
O
405 406
Regioselective dipolar cycloadditions of 4-nitro-, 5-nitro-, and 2-methyl-5nitro-1-vinylimidazoles
with nitrile oxides afford the corresponding 5-(imidazol-
1-yl)isoxazolines, which are potential intermediates in the synthesis of
aminoimidazole analogs of purine nucleosides (446). Isoxazole, isoxazoline and
isoxazolidine analogs of C-nucleosides, related to pseudo-uridine, have been synthesized
by 1,3-dipolar cycloaddition reactions of nitrile oxides and nitrones,
derived from mono- and disubstituted uracil-5-carbaldehydes and 2,4-dimethoxypyrimidine-5-carbaldehyde.
The dimethoxy derivatives have been easily deprotected
to the corresponding uracil, bearing the heterocyclic ring instead of a sugar
moiety (447).
Ph
N
N
O
O
O
R′