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

RR′C N
MeOCO
MeO
C
O
OBEt 2
N
O
O
+ −
BF2 O
2
C 5H 5N
R′
REACTIVITY OF NITRONATES 531
R
Scheme 3.107
N
O
OBEt 2
N
R′ = Me; R = H, Me, CMe2CO2Me,
CO 2Me; R = R′ = CO 2Me
are thermodynamically more stable than the starting nitronates (317). (Scheme
3.107).
3.4.2.5. Cyclic Nitronates The chemistry of cyclic nitronates substantially differs
from the chemistry of their acyclic analogs. Cyclic nitronates are involved
predominantly in various rearrangements rather than in elimination reactions. The
character and pathways of these rearrangements are determined not only by the
nature of the reagent used but also by the character of the heterocycle and the
nature of the substituents attached to the heterocycle.
Therefore, data on these compounds are difÞcult to summarize. Since certain
Þve- and six-membered nitronates are easily assembled from simple molecules,
some of the transformations considered in this section can be used for the development
of new promising strategies for organic synthesis.
3.4.2.5.1. Reactions with Nucleophilic and Electrophilic Agents Examples of
1,3-addition of these reagents to cyclic nitronates are virtually lacking. To our
knowledge, the reaction of phenylmagnesium bromide with 3,4,5-triphenylisoxazoline
2–N-oxide giving rise to the corresponding nitroso hemiacetal (318)
(Scheme 3.108) is the only exception.
It is unlikely that this reaction is of general character. In any case, alkylmagnesium
bromides give quite another product. The question whether other cyclic
nitronates can be involved in this reaction also remains to be established.
The reactions of ammonia or primary amines with Þve-membered cyclic
nitronates containing the EWG-group at the C-5 atom involve deoxygenation
of the nitronate fragment, aromatization of the ring, and amidation of the ester
Ph
Ph
O N
Ph
O
1. PhMgBr
2. H2O
Scheme 3.108
Ph
Ph
O N
Ph
Ph
OH