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

384 NITRONES: NOVEL STRATEGIES IN SYNTHESIS
b
H 2C
a
+ O
N
H
−
a: Rim addition; b: Spoke addition
a
b
Regioselective
Scheme 2.316
additions are not probable and that closed [6,6] additions are the most favored
ones, and follow a concerted mechanism (838).
Glyco-conjugated isoxazolidine-fused chlorins (768) and (769a–d) were prepared
in moderate to good yields by 1,3-dipolar cycloaddition reactions of
meso-tetrakis(pentaßuorophenyl) porphyrin (765) with in situ generated methylene
nitrone (766) and glycosyl nitrones (767a–d) (Scheme 2.318) (839, 840).
Porphyrin glyco-conjugates are of special importance due to their strong absorption
in the visible region above 700 nm. It makes these compounds very promising
for their potential application as photosensitizers in the photodynamic therapy
(PDT) of cancer.
O
H
N
H
N
2.9. KINUGASA REACTION ([2 + 2] CYCLOADDITION)
In 1972, Kinugasa and Hashimoto (841) reported the reaction of copper (I)
phenylacetylide with α,N -diphenylnitrone in dry pyridine. It has provided an
O
+
O
N
H