H. Adams et al., UNEXPECTED RING CONTRACTION IN THE BARIUM-ASSISTED CYCLOCONDENSATION OF 2,6-DIFORMYLPYRIDINE AND N,N-BIS(2-AMINOETHYL)-2-PHENYLETHYLAMINE, Journal of the Chemical Society. Dalton transactions, (6), 1996, pp. 1181-1183
The cyclocondensation reaction between N,N-bis(2-aminoethyl)-2-phenyle
thylamine and 2,6-diformylpyridine in the presence of a barium templat
e gave an unexpected 18-membered macrocyclic product in which a ring c
ontraction at one side-arm has occurred to produce an imidazolidine ri
ng.