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

560 NITRONATES
R
185 NO2
HX R′
R
X
186
O
N
R′
189
R′′
OSiMe3
R′′
R
H
OSiMe3
∗
X
∗
( ) n
H
N
O
R′
R′′
190
base
ISOC
X = O, S, N , CH2, C(CO2Me)2•
n = 1, 2.
R = H, Me, Ar.
R′ = H, Me, Ph.
() n
() n
+
R
X
Me 3SiCl/Et 3N
() n
187
R
X
NO2
(INOC)
R
R′
R′
A
R′′
PhNCO/Et 3N
N
R′′
O
N
∗
X
∗
O
∗
( ) n
R′
R′′
188
∗
X OH
∗
( ) n
R′
R′′
191
ISOC intramolecular silyl nitronate cycloaddition.
INOC intramolecular nitrile oxide cycloaddition.
Scheme 3.140
(intramolecular nitrile oxide cycloaddition (INOC) process) or undergo silylation
to form SENAs (189), as subjects of intramolecular cycloaddition, giving rise
to fused isoxazolidines (190) (ISOC process). The latter can be smoothly transformed
into bicyclic isoxazolines (188). Products (188) are readily reduced to the
corresponding γ-amino alcohols 191. It should be noted that the conÞgurations of
the labeled stereocenters are retained upon the transformation (190→188) due to
which, the stereochemistry of the INOC and ISOC processes can be compared.
R
() n