A Convenient Synthesis of 5-Trifluoromethyl-3-thiazolines and 5-Trifluoromethyl-2,3,4,5-tetrahydro-1,2,4-triazines

Abstract

5-Trifluoromethyl-3-thiazolines (3) and 5-trifiuoromethyl-2,3,4,5-tetrahydro-1,2,4 triazine (5) were conveniently synthesized from 3-(N-tert-butyl-N-methy1hydrazono)-1 ,I ,1-trifluoroalkan-2-ones (1) with the use of silica gel as an effective catalyst. 5-Trifluoromethylimidazole (6) was also obtained in good yield from 1.Fluorine-containing heterocycles are one of the most fascinating targets for synthetic organic chemists because of their potential biological activities1 Recently we reported an interesting cyclization reaction of 3-(N-tert-butyl-N-methylhydrazono)-l,1,1-trifluoroalkan-2-ones (1) which are readily preparable from aldehyde N-tert-butyl-N-methylhydrazones and trifiuoroacetic anhydride,2.3affording 5-trifluoromethyl-3-oxazolines (2).In this reaction, "we?' silica gel acts as an effective catalyst to give good yields of 2.4 Apparently oxygen atom in 2 derived from water adsorbed on "we?' silica gel.Above result suggests us that some other heteroatoms might be incorporated in heterocyclic ring system, if cyclization reaction was carried out in the presence of suitable heteroatom source and silica gel.This prompted us to try a synthesis of 5-trifluoromethyl-3thiazoline (3) from 1 and sulfurating reagents in the presence of silica gel as a catalyst.Now we wish to report our results.Several hydrazones ( I ) were prepared from the corresponding aldehydes by usual manner.2.3As