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

552 NITRONATES
OEt Ph
+ +
OEt NO2
+ +
Ph
O2N
O
Ph
O
O 15 kbar
O
48 h
15 kbar
20 h
Scheme 3.130
EtO
EtO
EtO
EtO
O O
N
Ph
O
O O
N
Ph
O O
N
Ph
O O
N
Ph
Et3N/MeOH
LiAlH4
51%
KCN
33%
O
O
O
Ph
Ph
OH
CO 2Me
This process is of a rather general character, and different types of oleÞns,
such as normal oleÞns, Michael substrates, inverted and strained oleÞns, can be
involved in such reactions. However, the interaction shown in Scheme 3.131
is accompanied by a number of side reactions, and consequently, the scope of
the transformation (161→162) and the yield of nitrosoacetals (162) substantially
depend on the nature of the substituent R.
The mechanism of this reaction has not been studied in detail. However, it
can be represented as a sequence of reactions. The Þrst reaction is, in fact,
[3 + 2]-cycloaddition of oleÞn to furoxan (161). Under severe conditions, the
resulting intermediate A undergoes fragmentation to give Þve-membered cyclic
nitronate B. The latter is involved in the usual addition reaction with an excess
of oleÞn to form isolable bicyclic product (162) (301, 378, 379).
An interesting example of the use of this process for the convenient stereoselective
synthesis of functionalized nitrosoacetals (163) was described in the
study (380) (Scheme 3.131, Eq. 2).