Process for preparing diketone compounds and precursors thereto

Abstract

A process for preparing compounds of the formula: wherein R 2 is lower alkyl; or phenyl optionally substituted by from one to five groups, the same or different, which are lower alkyl, lower haloalkyl, halogen or —SR 4 ; R 3 is halogen, lower alkyl, lower haloalkyl, lower alkoxy, lower haloalkoxy, —S-alkyl, cycloalkyl having from 3 to 7 carbon atoms in the ring, alkenyl or alkynyl having from 3 to 7 carbon atoms, or —(CR 5 R 6 )—SR 2 wherein q is one or two; R 4 is lower alkyl; R 5 and R 6 independently represent hydrogen, lower alkyl or lower haloalkyl; and n is zero or an integer from one to three; intermediate compounds of the formula: and processes for preparing them.

What is claimed is:  
     
         1 . A process for preparing a compound of formula (II) which comprises reacting a compound of formula (V) with a mercaptan HSR 2  of formula (IV) according to reaction scheme Sc2 indicated below:  
                   
       wherein: 
 R 2  is lower alkyl; or phenyl which is unsubstituted or is substituted by from one to five groups which are the same or different selected from the group consisting of lower alkyl, lower haloalkyl, halogen and —SR 4 ;  
 R 3  is halogen, lower alkyl, lower haloalkyl, lower alkoxy, lower haloalkoxy, —S-alkyl, cycloalkyl having from 3 to 7 carbon atoms in the ring, alkenyl or alkynyl having from 3 to 7 carbon atoms, or —(CR 5 R 6 )q—SR 2  wherein q is one or two;  
 R 4  is lower alkyl;  
 R 5  and R 6  independently represent hydrogen, lower alkyl or lower haloalkyl;  
 and n is zero or an integer from one to three.  
 
     
     
         2 . A process according to    claim 1   , wherein the reactant of formula (IV) is employed as solvent.  
     
     
         3 . A process according to    claim 2   , wherein the compound of formula (IV) is in the form of a mercaptan, and the reaction is performed in the presence of a base.  
     
     
         4 . A process according to    claim 3   , wherein the base is a hydroxide of an alkali metal or alkali earth metal, or a carbonate or hydride.  
     
     
         5 . The process according to    claim 1   , carried out in the presence of a catalyst.  
     
     
         6 . The process according to    claim 5   , wherein the catalyst is a phase transfer catalyst.  
     
     
         7 . The process according to    claim 6   , wherein the phase transfer catalyst is a quaternary ammonium salt.  
     
     
         8 . The process according to    claim 2   , carried out in the presence of a catalyst.  
     
     
         9 . The process according to    claim 8   , wherein the catalyst is a phase transfer catalyst.  
     
     
         10 . The process according to    claim 9   , wherein the phase transfer catalyst is a quaternary ammonium salt.  
     
     
         11 . The process according to    claim 3   , carried out in the presence of a catalyst.  
     
     
         12 . The process according to    claim 11   , wherein the catalyst is a phase transfer catalyst.  
     
     
         13 . The process according to    claim 12   , wherein the phase transfer catalyst is a quaternary ammonium salt.  
     
     
         14 . The process according to    claim 4   , carried out in the presence of a catalyst.  
     
     
         15 . The process according to    claim 14   , wherein the catalyst is a phase transfer catalyst.  
     
     
         16 . The process according to    claim 15   , wherein the phase transfer catalyst is a quaternary ammonium salt.  
     
     
         17 . A process for the preparation of a compound of formula (VI):  
                   
       wherein: 
 R 3  is halogen, lower alkyl, lower haloalkyl, lower alkoxy, lower haloalkoxy, —S-alkyl, cycloalkyl having from 3 to 7 carbon atoms in the ring, alkenyl or alkynyl having from 3 to 7 carbon atoms, or —(CR 5 R 6 )q—SR 2  wherein q is one or two;  
 R 5  and R 6  independently represent hydrogen, lower alkyl or lower haloalkyl;  
 and n is zero or an integer from one to three; which comprises reacting a compound of formula (VII):  
                 
 
 in which R 3  and n are as defined above and X is halogen, with nitroethane, wherein the reaction is performed in the presence of a base selected from the group consisting of a hydroxide, a carbonate, a hydride, an alkoxide of an alkali or alkaline earth metal, and guanidine; in the presence of a solvent selected from the group consisting of nitroethane and an inert solvent.  
 
     
     
         18 . A process according to    claim 17   , wherein the reaction temperature is from 0° C. to 50° C.  
     
     
         19 . A process according to    claim 18   , wherein the reaction is performed in the presence of a phase transfer catalyst.  
     
     
         20 . A process according to    claim 19   , wherein the phase transfer catalyst is a quaternary ammonium salt.  
     
     
         21 . A process according to    claim 17   , wherein the reaction is performed in the presence of a phase transfer catalyst.  
     
     
         22 . A process according to    claim 21   , wherein the phase transfer catalyst is a quaternary ammonium salt.  
     
     
         23 . A compound of the formula (II):  
                   
       wherein: 
 R 2  is lower alkyl; or phenyl which is unsubstituted or is substituted by from one to five groups which are the same or different selected from the group consisting of lower alkyl, lower haloalkyl, halogen and —SR 4 ;  
 R 3  is halogen, lower alkyl, lower haloalkyl, lower alkoxy, lower haloalkoxy, —S-alkyl, cycloalkyl having from 3 to 7 carbon atoms in the ring, alkenyl or alkynyl having from 3 to 7 carbon atoms, or —(CR 5 R 6 )q—SR 2  wherein q is one or two;  
 R 4  is lower alkyl;  
 R 5  and R 6  independently represent hydrogen, lower alkyl or lower haloalkyl;  
 and n is zero or an integer from one to three.  
 
     
     
         24 . The compound according to    claim 23   , which is 2-methylthio-4-trifluoromethylacetophenone or 3,4-dichloro-2-(methylthio)acetophenone.