Vinyl halides, reaction with ketoximes

General synthesis of pyrroles and 1-vinylpyrroles by the reaction of ketoximes with acetylenes and their synthetic equivalents (vinyl halides and dihaloethanes) in the presence of the strongly basic KOH/DMSO system (Trofimov reaction) has been reviewed ° in recent years. Therefore, in the present work this reaction will be described very shortly. In principle, pyrrole (51) synthesis can be carried out as a one-pot procedure by treating ketones (49) with hydroxylamine and then reacting the ketoximes (50) formed with acetylenes (equation 22). 

The reaction of ketoximes with vinyl halides at 80-130°C in the presence of alkali metal hydroxides and DMSO leads to pyrroles (80ZOR672) (Scheme 55). Varying the ratio of reactants and the conditions, it is possible to carry out the reaction selectively and obtain either pyrroles (R3 = H) in about 40% yield or their W-vinyl derivatives (yield to 35%). 

In the preparation of pyrroles and N-vinylpyrroles from ketoximes, along with vinyl halides, dihaloalkanes as acetylene equivalents can also be used. Pyrroles and /V-vinylpyrroles are formed in a yield of about 30% in the reaction of ketoximes with dihaloalkanes in the presence of excess alkali metal hydroxide in DMSO (Scheme 60) (79IZV2840). 

The present methods for the preparation of N acyl a arylenamides include (i) reductive acylation of ketoximes with iron metal [2] or phosphines [3] in the presence of acyl chlorides or acyl anhydrides (Method A) (ii) metal catalyzed coupling of vinyl halides [4], triflates [5], or tosylates [6] with amides (Method B) (iii) reaction of imine intermediates derived from nitriles with acyl chlorides or anhydrides (Method C) [7] and(iv) Pd catalyzed coupling ofaryl tosylates with N acyl vinylamines (MethodD) [8]. 

Along with vinyl halides as synthetic equivalents of acetylene, dihaloethanes can also be employed in the synthesis of pyrroles and N-vinylpyrroles from ketoximes (Scheme 1.129) [299], The reaction of ketoximes with dihaloethanes in the presence of excess of alkali metal hydroxide in DMSO gives pyrroles and N-vinylpyrroles in -30% yields. In further experiments, higher yields have been achieved [7],... 

SCHEME 1.128 Reaction of ketoximes with vinyl halides in MOH/DMSO systems. 

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