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

298 NITRONES: NOVEL STRATEGIES IN SYNTHESIS
Me
H
O
N H
O
N
Me
H
O N
Me H
O
N
Me
O
_
Scheme 2.210
N
Me
Me
H
O
N H
O Me
N
design of complex molecule structures, such as key building blocks of chiral
ligands, alkaloids, antibiotics, and other biologically active compounds. Introduction
of the oleÞnic component and nitrone fragment into a molecule can be
realized in different ways and in various sequences. Depending on the distance
between them, and conformational mobility of the connective fragments, various
polycyclic structures can be obtained.
In Scheme 2.210, possible variants of intramolecular 1,3-dipole cycloaddition
of norbornadiene derivatives with 2-substituted norbornadiene-tethered nitrones
are presented.
These reactions give regio- and stereoisomers in satisfactory yields (Table
2.16) (702).
The most convenient and frequently used systems for carrying out intramolecular
1,3-cycloaddition reactions are systems (a–f) with various mutual arrangements
of the nitrone group and oleÞnic fragment. In systems (a–d), the substituent
with the oleÞnic fragment is situated at the α-C , while in (e) and (f)
the substituent is attached at the N atom. Depending on the connecting chain
length and the location of the X (X = CH2, O, NR, S) group, intramolecular
1,3-cycloadditions give different polycyclic systems (Scheme 2.211).
+
Me
N
O
H