3-Trifloxypropene iminium and propyne iminium salts derived from N-allyl-,N-homoallyl-, and N-benzyl-substituted semicyclic enaminones

The novel semicyclic enaminoketones 3a-n, featuring N-allyl, N-homoalIyl, N -benzyl, and N-4-chorobenzyl substitution, have been prepared. Their reacti on with triflic anhydride leads to 3-trifloxypropene iminium triflates 4 wh ich are transformed into semicyclic propyne iminium triflates 5 by thermal beta-elimination of triflic acid (HOTf). If a 4-chlorophenyl group is attac hed to the TfO-substituted carbon atom, salts 4 can be isolated (4a,d,g,h,k ,m) and converted into propyne iminium triflates 5 at 120 degrees C. The pr esence of a 2-thienyl or 3-thienyl group adjacent to the trifloxy group pre vents the isolation of 4 since HOTf elimination occurs already below room t emperature. Thus, salts 5b,c,e,f,i,j,l,m,n are obtained directly from enami noketones 3 and triflic anhydride.