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Reakcje [2+3] cykloaddycji sprzężonych nitroalkenów z nitronami

Barański A., Jasiński R.

Wiadomości Chemiczne

2002

[Z] 56, 9-10

829-854

The work is an attempt of systematizing of the literature data concerning the regio- and stereoselectivity of [2+3] cycloadditions of conjugated nitroalkenes to nitrones. In most cases these reactions are regiospecyfic leading to the corresponding 4-nitro-isoxasolidines. In the reactions with trans-b-arylnitroethylenes, trans-configuration of the substituents at C-3 and C-4 positions of the heterocyclic ring is always favored. However, in the case of trans-b-alkylnitroethylenes, usually the 3,4-cis-isomers are formed in majority. If steric effects do not affect significantly the reaction course, the observed regioselectivity can be well explained in the terms of FMO or HSBA theory. The reaction stereoselectivity is hard to predict in advance. It seems that it depends on the equilibrium between the two complementary interactions in the reaction transition state: the attractive secondary overlaps of the reactants pz-orbitals, and the repulsive steric interactions of the reactants substituents. In some cases, the possibility of (Z)-(E) isomerisation of nitrones under reaction conditions has to be taken into account. Chemical properties of the cycloadducts resulting from the presence of nitro group in the isoxazolidine ring have also been discussed.