these compounds was studied under acidic conditions (PTSA) and over a well defined range of concentrations (c = 0.1−0.2 M). While cis amide 9 and mixtures of cis and trans rotamers 10−12 resulted practically exclusively in the formation of seven-membered ring lactams 22−25, trans compounds 1 and 3−8 afforded fourteen-membered ring bislactams 2, 13−18, the formation of which involves a dimerization.