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

P
R
P
R P R
ArCNO
−78 °C −r. t.
Et2O or MePh
R = t-Bu, 2-methylbut-2-yl,
1-methylcyclopentyl
(Ar = Ph)
−MesCN
REACTIONS OF NITRILE OXIDES 59
(Ar = Mes)
Scheme 1.33
Ar
Ar
N O
N O
P
R
Ar
R
P
R
O N
P
192
R
P
P
193
O
P
R
O
N
R
O
Benzonitrile oxide and mesitonitrile oxide undergo 1,3-dipolar cycloaddition
reactions with 1,3,5-triphosphinines under mild conditions to afford fused heterocyclic
compounds (Scheme 1.33), for example, 192 and 193. Oxaphosphazoles
and oxadiphospholes have become accessible by thermal fragmentation reactions
of such fused heterocyclic compounds (358).
Low-valence metal carbonyl complexes give in good yield (50%–85%),
Þve-membered metalacycles by 1,3-dipolar cycloaddition of aromatic nitrile
oxides to a M–CO bond. Synthesis of metalacycles from metalacarborane carbonyl
anions [closo-3-PPh3-3-(CO)-3,1,2-MC2B9H11] − (M = Ir, Rh) and
[closo-2-PPh3-2-(CO)-2,1,7-RhC2B9H11] − , from a number of pentamethylcyclopentadienyl
and cyclopentadienyl complexes of Co, Rh, and Ir of the type
(η 5 -C5R5)ML(CO) (R = H, Me; L = PPh3, PMe3, CO) and from the metal carbonyl
anions M(CO)5 − (M = Mn, Re) have been described (359). Single-crystal
X-ray diffraction studies of the rhodaisoxazolinone metalacycles, for example,
194 (L is carborane ligand) have also been reported. The reaction of rhodium
complex C5H5Rh(CO)(L) [L = P(CHMe2)3], which is prepared from C5H5
Rh(CO)2 and neat triisopropylphosphine, with benzonitrile oxide and 2-chlorobenzonitrile
oxide affords metalaheterocycles 195 in 90% to 95% yield. The
X-ray structural analysis of 195 (R = H) reveals the presence of an almost planar
RhCONC heterocycle in which the two Rh–C distances differ by 0.045 ûA (360).
Kinetically stabilized germanothiones Tbt(Tip)Ge = S, Tbt(Dis)Ge = S and
germanoselones Tbt(Tip)Ge = Se, Tbt(Dis)Ge = Se [Dis = bis(trimethylsilyl)
methyl, Tbt = 2,4,6-trisbis(trimethylsilyl)methylphenyl, Tip = 2,4,6-tris(isopropyl)phenyl],
have been synthesized and have shown to enter 1,3-dipolar
cycloaddition reactions with mesitonitrile oxide (361).
Ar
N
A