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

X-C(NO 2) 3
NO 2-C(NO 2) 3
R
R′
CH 2 CH 2
R′′
(NO2)3C − +
(NO 2) 3C −
R′′
SYNTHESIS OF NITRONATES 443
O
X X N
R
NO2
+
Scheme 3.10
R′
R′′
O 2N
NO2
NO2 N
O O
3
NO 2
O
NO 2
CH2 CH2
X = CN, NO 2, I, F
R
R′
C(NO 2) 3
Tetranitromethane (X=NO2) acts as an electrophile toward oleÞns to give the
corresponding ion pairs. Their further behavior depends on the nature of oleÞn. In
the case of ethylene (26, 27), allyl ethers (28), and other monosubstituted alkenes
(29–31), nitronates (2) that are generated through C,O-coupling of preceding
ionic intermediates are involved in [3 + 2]-addition reactions with oleÞns that
are present in the reaction mixture to give isoxazolidines (3) in moderate yields
(Eq. 1). (Rather large amounts of intermediate nitronates (2) can be detected in
reaction mixtures prepared with the use of particular branched oleÞns (30) or
dienes (28).)
To the contrary, only C-alkylation of the trinitromethane anion with these
intermediates is observed (32, 33) if the cations in the ion pair are stabilized by
one or two alkyl substituents at the α-carbon atom (Eq. 2).
Other trinitromethane derivatives (X=CN (34), I (35), or F (36)) are involved
in analogous processes.
3.2.2. Synthesis of Cyclic Nitronates
Five- and six-membered cyclic nitronates are generally considered as cyclic
nitronates. Scheme 3.11 presents two most general approaches to the synthesis
of such compounds.
One of these methods involves intramolecular cyclization of specially prepared
precursors A or B (Eq. 1). These precursors can be synthesized from readily
available AN by classical reactions, many of which will be considered in detail
below.
2
X
(1)
(2)