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

568 NITRONATES
Me 2Si
R 1
R 2
R 1
R
NO2
Me 2Si
R 2
Me3SiCl/Et3N
CH2Cl2, 12 h
R
O
N
Me2Si
+
R 1
211 60%–80%
dr– 7/1 – 20/1
R 1
H
R 2
Me2Si
H
R
N
O
OSiMe 3
R
O
N
R2 212 OSiMe3 R and R 2 – H or Me; R 1 – BuO(CH 2) 2; n-Pr; n-Hex; BuOCH 2CHMe
Ph
O2N
R
O
SiPh2
O
Me3SiCl/Et3N
benzene, ref.
1 day
Ph
H
O
O
SiPh2 N O
R
212′a,b
Ph
O
N
Me3SiO
R
O
SiPh2
O
Ph
H
O
O
SiPh2 N O
212a,b
a–R = Me, 45%, 2/2′ = 7:3
b–R = Ph, 23%, 2/2′ = 9:1
Scheme 3.149
In the INOC process, the stereoselectivity of both reactions shown in Scheme
3.149 is substantially lower compared to that in ISOC; however, the yield of
isoxazolines (211) and (212a,b) is noticeably higher.
In intramolecular [3 + 2]-cycloaddition reactions of Þve-membered cyclic
nitronates, only a Si-containing tether was used (393) (Scheme 3.150, see also
Scheme 3.120 and references therein).
This process was carried out with the use of diastereomerically and enantiomerically
pure Þve-membered cyclic nitronates (213). After selective silylation
of the hydroxy group and intramolecular cycloaddition, these compounds give
enantiomerically pure fused systems, which are similar precursors of enantiomerically
pure hydroxyamino acids and other polyfunctional compounds possessing
potential biological activity.
R
(1)
(2)