Abstract The adduct 2 of methylamine with two molecules of cyclopropanone gives, on mild heating, a variety of six-and eight-membered heterocycles (with hetero-atoms NNN, NON, ONO, NONO or ONOO) and three or four unruptured (spiro-) cyclopropyl groups attached to the ring. The cyclisation mechanism involves in all cases an initial rapid dimerisation of 2.