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

222 NITRONES: NOVEL STRATEGIES IN SYNTHESIS
observed. “Spin trapping” has received wide application in the study of radical
processes using spin traps (3). However, in some cases nitrone performance in
radical reactions is of synthetic value.
2.6.4.1. Addition of C-Radicals to Nitrones Recently (525), the addition of
alkyl radicals to chiral nitrones as a new method of asymmetrical synthesis of
α-amino acids has been described. Addition of ethyl radicals to glycosyl nitrone
(286) usingEt3B as a source of ethyl radicals appears to proceed with a high
stereo-control rate.
Nitrone (286) reacts readily with nucleophilic ethyl radicals to give the
expected ethyl product (288) in 50% yield as the only diastereomer, as well
as a 32% yield of the C,O-diethyl product (289) and trace quantities of ethyl
Ph
Ph
Et 2B
Et 3B
•Et
O O
N
O
O2
+
Et
Ph
Ph
H2O
Et3B
O O
+
N
O
−
286
Ph
O O
Ph
Ph
Ph
Ph
Ph
O O
N
O− •
287A
N
O
Et
O O
287B
Ph N Et Ph N Et Ph N
OH
OEt
−
O
288a
289 290a
Scheme 2.109
+
•
Et
O O
Ph
O O
+
Et