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

156 NITRONES: NOVEL STRATEGIES IN SYNTHESIS
R =
O
HO
HO
HO
O
O
D-Mannose
CH3,
H H
O
O O
69
S
OH
+
N
O
−
1) acetone, P2O5
Ca(OH) 2, carbon
2) HONH 2-HCl, NaOAc
EtOH, Δ, 1h
R
218
,
RCHO
Na 2SO 4
CH 2Cl 2
O
OH
O
O
O
Bn
H H
O
O O
68a
H
OH
O O
68b
OH
CH 2OBn, CH 2OTIPS, CH 2OTBDPS,
Scheme 2.24
NHOH
NOH
Bn(2,6-diF)
Another synthetic approach for generating sugar-containing nitrones is by initial
treatment of sugars with unsubstituted hydroxylamine. The resulting cyclic
hydroxylamine of the tautomeric mixture (68a) and of the open chain oxime
(68b) react with aldehydes to give the corresponding nitrones (69) (Scheme 2.24)
(216–220).
The chirality source in the synthesis of optically active nitrones (71) and (72)
are known to be enantiopure chiral benzyl type hydroxylamines, (R)-α-methylbenzylhydroxylamine
(70a) and (R)-α-(hydroxymethyl)-benzylhydroxylamine
(70b) (Scheme 2.25) (221).
The main building block of PEDC (1-phenyl-2-[(S)-1-aminoethyl]-N,N -diethylcyclopropanecarboxamide),
a potent NDMA (N -methyl-D-aspartic acid)
receptor antagonist of a cyclopropane structure, N -benzyl-C-cyclopropyl nitrone
O
O
219
220
,