Process for the preparation of nitroalkenes

Abstract

A process for the nitration of conjugated alkenes of formula (I) wherein R, R 1 , R 2 , R 3 and R 4 have the meanings reported in the description, which allows to obtain the corresponding β-nitro-alkenes, characterised in that the nitrating agent is a mixture of an inorganic nitrite and iodine in the presence of an oxidising agent is described.

1 ) A process for the nitration of conjugated alkenes of formula  
       
         
           
           
               
               
           
         
       
       wherein 
 R is a hydrogen atom, an optionally substituted phenyl, a linear or branched C 1 -C 4  alkyl; R 1  is a hydrogen atom or a linear or branched C 1 -C 4  alkyl, optionally substituted by an OH or C 1 -C 4  alkoxy group; R 2 , R 3  and R 4 , the same or different, are selected among hydrogen and halogen atoms, linear or branched C 1 -C 4  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 R 2 , R 3  and R 4 , in ortho between them, form a methylendioxy group; or R 1  together with R 2  forms a cyclic system with 5-7 terms condensed with the aromatic ring and optionally containing an oxygen atom; or R 1  together with R forms a cyclic system with 5-7 terms;  
 which allows to obtain β-nitro-alkenes of formula  
                     
 wherein R, R 1 , R 2 , R 3  and R 4  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:  
 
     
     
         2 ) A process according to  claim 1  wherein the iodine is in an amount from 0.1 to 0.8 moles per mole of the compound of formula I.  
     
     
         3 ) A process according to  claim 1  wherein the inorganic nitrite is selected among silver nitrite, sodium nitrite and potassium nitrite.  
     
     
         4 ) A process according to  claim 3  wherein the inorganic nitrite is sodium nitrite.  
     
     
         5 ) A process according to  claim 1  herein the inorganic nitrite is m an amount from 2 to 4 moles per mole of the compound of formula I.  
     
     
         6 ) A process according to  claim 1  wherein the oxidant agent is selected among peracids, oxygen peroxide and inorganic nitrites.  
     
     
         7 ) A process according to  claim 6  wherein the oxidant agent is a mixture of peracetic acid, oxygen peroxide and water.  
     
     
         8 ) A process according to  claim 1  wherein the iodine is formed in situ from alkaline iodides.  
     
     
         9 ) A process according to  claim 1  wherein the temperature is from 40° C. to 50° C.  
     
     
         10 ) A process according to  claim 1  for the nitration of styrenes, optionally substituted on the aromatic ring by from 1 to 3 methoxy groups or by a methylenedioxy group.  
     
     
         11 ) A process according to  claim 1  for the nitration of dihydronaphthalenes, optionally substituted by methoxy, methyl, ethyl, fluoro, chloro, bromo, iodo, carboxy, methoxycarbonyl groups or by a methylenedioxy group.  
     
     
         12 ) A process according to  claim 11  for the nitration of dihydronaphthalenes of formula  
       
         
           
           
               
               
           
         
       
       wherein 
 R 3A  and R 4A , the same or different, are hydrogen atoms, methoxy, methyl, ethyl, fluoro, chloro, bromo, iodo, carboxy, methoxycarbonyl groups or, together, form a methylenedioxy group;  
 R is a hydrogen atom, an optionally substituted phenyl, a linear or branched C 1 -C 4  alkyl.  
 
     
     
         13 ) A process according to  claim 1  for the nitration of benzopyranes optionally substituted by methoxy, methyl, ethyl, fluoro, chloro, bromo, iodo, carboxy, methoxycarbonyl, aminocarbonyl or methylaminocarbonyl groups.  
     
     
         14 ) A process according to  claim 13  for the nitration of the benzopyranes of formula  
       
         
           
           
               
               
           
         
       
       wherein 
 R 3B  and R 4B , the same or different, are hydrogen atoms, methoxy, methyl, ethyl, fluoro, chloro, bromo, iodo, carboxy, methoxycarbonyl, aminocarbonyl or methylaminocarbonyl groups;  
 R is a hydrogen atom, an optionally substituted phenyl, a linear or branched C 1 -C 4  alkyl.  
 
     
     
         15 ) A process according to  claim 13  for the nitration of the compound 8-fluoro-2H-chromene-5-carboxylic acid amide.