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Conversion of carbonyl function to nitro group (retro-Nef reaction) [21] is an important method for the preparation of nitro compounds. Such conversion is generally effected via oximes using strong oxidants (Scheme 1.12).

Scheme 1.12 Retro-Nef reaction via oximes.

Following a pioneering procedure performed with CF₃CO₃H [22], there was reported a revised and improved procedure (Scheme 1.13) [23] using peroxytrifluoroacetic acid obtained through reaction of urea–hydrogen peroxide complex (UHP) with trifluoroacetic anhydride (TFAA) in acetonitrile at (0 °C).

Scheme 1.13 Oxidation of oximes with TFAA/UHP.

The procedure allows good yields with aldoximes, while fails to react with ketoximes. On the other hand, ketoximes can be converted into secondary nitroalkanes, following the Olah method [24], oxidizing ketoximes with sodium perborate in glacial acetic acid. However, this procedure failed with aldoximes.

An interesting conversion of both aldoximes and ketoximes to the corresponding nitroalkanes has been realized by a complementary synthetic route of the UHP method. In fact, the oxidation achieved with “Benz-Mo,” the Mo(VI) oxidiperoxo complex [Benz-MoO(O₂)₂]⁻(t-Bu)₄N⁺ in acetonitrile, affords good yields of both primary and secondary nitroalkanes (Scheme 1.14) [25].

Scheme 1.14 Oxidation of oximes using Benz-Mo.