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

314 NITRONES: NOVEL STRATEGIES IN SYNTHESIS
H
EtO2C EtO2C EtO2C O HON N
O
BnNHOH
O
Scheme 2.232
C6H6 Δ
H
O
N
H
O
N
Ph
Ph
NC
cis trans
Scheme 2.233
H
O
H
N
OSi(Ph)2 t Bu
O
N
Bicyclic cis- and trans-isoxazolidinyldiynes have been prepared by intramolecular
nitrone cycloaddition of the two side chains of an acyclic enediynenitrone
precursor (Scheme 2.233) (731).
Intramolecular 1,3-dipolar cycloaddition reactions of N -(3-alkenyl)nitrones, as
presented in Scheme 2.211e, led to the synthesis of polyhydroxy derivatives of
quinolizidine (474) and indolizidine (475) (Scheme 2.234) (732).
According to Scheme 2.211f, heating of nitrones (476a,b) in toluene gave
bridged bicyclic compounds (477a,b), as the major reaction products (Scheme
2.235) (704).
2.8.1.2. Intermolecular Reactions Intermolecular 1,3-dipolar cycloaddition
reactions of nitrones to oleÞns seem to be the most studied. They are widely
used for the synthesis of different enantiomerically pure compounds, including
biologically active ones. For example, two new glycosidase inhibitors have been
obtained by the nitrone cycloaddition strategy (Fig. 2.32) (733).
The optically active isoxazolidines obtained in these cycloaddition reactions
can be easily transformed into biologically active β-amino acids, into β-lactams
and into important chiral building blocks such as γ-amino alcohols. The multitude
of synthetic results in these reactions is of course expected by the wide variety
−
+
+
H
Ph