The alkylation of 4-benzyl-2-phenyl-1,3-oxazol-5(4H)-one (11) with
ω-azidoalkyl iodides (12) by deprotonation with LDA in THF/HMPT at –78 °C
yielded mixtures of the 4,4-disubstituted 1,3-oxazol-5(4H)-ones (13) and the O-alkylated 1,3-oxazoles (14) in 65–50%, with 13 as the major product. The reaction of the latter with dimethylamine in acetonitrile at room temperature led to ω-azido-2-benzamido-2-benzylalkane amides (15), which were reduced to give the corresponding ω-amino derivatives (16). On treatment with HCl gas or BF3 in boiling toluene, the macrocyclic 2-benzamido lactams (18) were formed in up to 27% yield via the intermediate formation of 1,3-oxazol-5(4H)-ones (17). The structures of the 14- and 15-membered lactams have been established by X-ray crystallography.