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

REACTIONS WITH CYCLOPROPANES 397
O O
N
O O
Me O
O O
O O
Ph
O N
−
+
30 mol%, CLA
+
CH2Cl2 , 0.1 M, r.t.
4 A MS
Ph
795 796 797
O
R 2
N
R 1
798 e
1
2
3
4
5
6
7
8
9 c
10 d
O
N
N
O
N
Yb(OTf)3
Yb(OTf)3
Yb(OTf)3
Yb(OTf)3
Cu(OTf)2
Cu(OTf)2
MgI2
Ni(ClO4)2
Ni(ClO4)2
Ni(ClO4)2
N
O
O
R 1
N
R 2
798 f
N
798 a R 1 = i-Pr; R 2 = H
b R 1 = i-Pr; R 2 = H
c R 1 = Ph; R 2 = H
d R 1 = R 2 = H
Entry Lewis acid Ligand 798 time/days Yield (%) a ee (%) b
a
b
c
d
e
f
f
g
g
g
a Isolated yield
b Determined by chiral HPLC
c No MS 4 Å
d THF as a solvent with MS
3
6
3
3
7
6
6
2
2
2
Scheme 2.331
O
50
90
76
87
-
47
75
96
51
88
O
N
Ph
28
10
02
18
-
37
34
89
89
90
O
798 g
that capture of the zwitterion by the nitrone occurs stepwise (855). Comparative
analysis of chiral catalysts (CLA) in enantioselective addition of nitrone (796) to
1,1-cyclopropane diesters (795) has been made (855). Reactions with ytterbium
trißate as a Lewis acid, and of a variety ligands led to low enantioselectivity
N
Ph
O