The possibility for five-membered ring formation, i.e., head-to-head and tail-to-tail additions, in anionic cyclopolymerization of 1,6-dienes was investigated using N-tert-butyl-N-allylacrylamide (BAA), N-2,6-xylyl-N-allylacrylamide (XAA), NN-diallylacrylamide (DAA), and N-methyl-N-allylacrylamide (MAA) as monomers and tert-butyl magnesium chloride as an initiator. It was found that BAA forms polymers, with five-membered rings as a repeating cyclic unit and, in addition, the degree of cyclization of poly(BAA) obtained was about 81%, in spite of the fact that the anionic polymerization tendency of an allyl group is extremely low. XAA, DAA, and MAA yielded polymers without any cyclized units leaving the allyl group as pendant unsaturation. Conformational analysis of these monomers suggested that only BAA has favorable conformation for five-membered ring formation. C-13 NMR spectroscopic studies revealed that conjugations between C=C and C=O double bonds of BAA and XAA are less effective than those of DAA and MAA probably due to steric hindrance. This indicates that the propagating anions derived from acryloyl groups of the former are more active than those of the latter. Based on these results it has been concluded that conformational advantage of BAA and higher reactivity of propagating anion derived from its acryloyl group make possible this unusual addition reaction to form rive-membered ring.