Process for the preparation of nitroalkenes

1) A process for the nitration of conjugated alkenes of formula

• 7
• wherein
• R is a hydrogen atom, an optionally substituted phenyl, a linear or branched C1-C4 alkyl;
• R1 is a hydrogen atom or a linear or branched C1-C4 alkyl, optionally substituted by an OH or C1-C4 alkoxy group;
• R2, R3 and R4, the same or different, are selected among hydrogen and halogen atoms, linear or branched C1-C4 alkyl or alkoxy groups, carboxylic groups, aminocarbonyl groups, alkyloxycarbonyl, alkylcarbonyl, mono- or di-alkylaminocarbonyl, alkylcarbonylamino and alkylcarbonyloxy groups having from 1 to 4 carbon atoms in the alkyl moiety;
• or two of R2, R3 and R4, in ortho between them, form a methylendioxy group;
• or R1 together with R2 forms a cyclic system with 5-7 terms condensed with the aromatic ring and optionally containing an oxygen atom;
• or R1 together with R forms a cyclic system with 5-7 terms;
• which allows to obtain β-nitro-alkenes of formula
• 8
• wherein R, R1, R2, R3 and R4 have the already reported meanings;
• characterised in that the nitrating agent is a mixture of an inorganic nitrite and iodine in the presence of an oxidising agent: