3-Trifloxypropene iminium and propyne iminium salts derived fromN-Allyl-,N-Homoallyl-, and N-benzyl-substituted semicyclic enaminones

Abstract

The novel semicyclic enaminoketones 3a-n, featuring N-allyl, N-homoallyl, N-benzyl, and N-4-chlorobenzyl substitution, have been prepared. Their reaction with triflic anhydride leads to 3-trifloxypropene iminium triflates 4 which are transformed into semicyclic propyne iminium triflates 5 by thermal β-elimination of triflic acid (HOTf). If a 4-chlorophenyl group is attached 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 °C. The presence of a 2-thienyl or 3-thienyl group adjacent to the trifloxy group prevents the isolation of 4 since HOTf elimination occurs already below room temperature. Thus, salts 5b,c,e,f,i,j,l,m,n are obtained directly from enaminoketones 3 and triflic anhydride