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

34 NITRILE OXIDES
O O
O
Br
ArCNO
ArCNO
−HBr
O N
O
79 80
O
81
Ar
O N
Scheme 1.23
NiO 2
Ar
O N
providing mixtures of regioisomers; however some substituted norbornene and
dicyclopentadiene derivatives give a single isomer. Experimental observations
concerning dicyclopentadiene derivatives were investigated via a gas phase and
solvent model, MO calculations on the transition-state geometries at semiempirical
(PM3), and hybrid ab initio-DFT levels (244).
Reactions of methoxycarbonylformonitrile, furonitrile and substituted benzonitrile
oxides (4-Me, 4-OMe, 3-OMe, 4-Cl, 3-Cl, 2,4-di-Cl, 4-F as substituents)
with dimethyl 7-(diphenylmethylene)bicyclo[2.2.1]hept-2-ene-5,6-dicarboxylate
led exclusively to exo cycloadducts 82 (R = CO2Me, 2-furyl, substituted phenyl),
which, on irradiation with a low-pressure mercury lamp, afforded 3-azabicyclo
[4.3.0]nonadiene-7,8-dicarboxylates 83 as the only products. The 1,3-dipolar
cycloaddition, followed by a photorearrangement, provides a new method for
obtaining tetrahydro-2H -pyridine derivatives from cyclopentadiene (245).
MeO 2C
MeO 2C
Ph
82
Ph
O
N
R
Ph Ph
N
MeO2C MeO2C CHO
Nitrile oxides react with cycloheptatriene and its tricarbonyliron complex to
give mixtures of adducts. In particular, for the complex, these adducts are 84, 85
(regioisomers at the uncomplexed double bond) and bisadduct 86. The regioselectivity
of the reactions of cycloheptatriene is similar to that of the reactions of
its tricarbonyliron derivative (246).
83
R
Ar