Empleando reacciones tipo Mannich en medio alcalino entre fenoles para-sustituidos y 1:3,7;9,13;15,19;21-tetrametilentetrahexahidropirimidina (TMTP) se logró sintetizar compuestos de estructuras tipo 1,3-hexahidropirimidina. Las estructuras se elucidaron por métodos espectroscópicos. Los compuestos sintetizados no se encuentran descritos en la literatura. /Abstract By a Mannich-type reactions in alkaline medium between para-substituted phenols and 1:3,7: 9,13:15,19:21-tetrametilentetrahexahidropirimidine (TMTP) was succeeded in synthesizing compounds of structures (1,3-hexahidropirimidine). The structures of these compounds were established by spectroscopic methods. To our knowledge the synthesized compounds are not described in the literature.