By contrast with the aminomethylation of thiourea by formaldehyde and primary amines to form 5-substituted 1,3,5-triazinane-2-thiones (see studies [1,2] and references therein) the aminomethylation of urea has not attracted so much work [3-10], the most recent being published in 1991. Because of the possibility of different condensations involving urea and formaldehyde [11,12] cyclic urea Mannich bases are better obtained not by a three-component condensation of urea, formaldehyde, and the corresponding primary amine [3-5, 7] but rather using 1,3-dimethylolurea (DMU) (1) [13], prepared from urea and formaldehyde, which then condenses with a suitable primary amine [7,8] or by condensing urea with the previously prepared dimethylol derivative of a primary amine with or without isolation of the indicated intermediate product [9]. The N-methylene derivative of a primary amine [10] may be used in place of the latter. Ethylenediamine and ethanolamine have been used [3][4][5] as bifunctional amines in a three-component condensation and ethanolamine and N,N-dimethylethylenediamine [7] in the condensation with DMU. In all four cases the expected 5-substituted 1,3,5-triazinan-2-one cyclic Mannich bases were obtained.

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Methylation of the phenyliminooxazolidinone (I) gives a mixture of the (methylphenylamino)oxazolinone (III) and the 3‐methyloxazolidinone (IV).

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