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

R
R
O2N
O2N
O N
Regioselectivity
+
O
N
Stereoselectivity
O N
+
O
N
N
OMe
R
NO 2
O
O
O
OR′
OR′
R′′
>
R
O
N
head-to-head
O
N
OR′
R
head-to-tail
REACTIVITY OF NITRONATES 545
O
O
R N
OR′ R
H
N
H
R′′
exo
O
N
OR′
R
R′′
endo
Scheme 3.127
(H)Alk O
N
Alk OMe
Ref.162, 337
R
O N O
OR′
(H)Alk
NO2
Alk
O N O
R
R
O
N
OSi
R
CO2Me
>> > >
O N
CO 2Me
> ~
O
O N
CH 3
O
>
O N
COMe
O
O N O
O N
O
O
N
N
R′′
trans
O
N
OR′
R′′
cis
O N
> > >
Chart 3.10
>
OR′
OR′
OR′
Ref.162
R
O
Ref.57
Ph
O N O
CN
Ref.337
Ph
O
O N
On the whole, the introduction of alkyl substituents at the α-carbon atom
leads to a sharp decrease in the rate of [3 + 2]-cycloaddition, that is, nitronates
derived from primary AN react much faster than nitronates derived from analogous
secondary AN. The introduction of functional EWG groups leads to a
substantial increase in the rate of [3 + 2]-cycloaddition. It can also be noted that
O