An efficient and three-step procedure for the synthesis of novel 6,7-dihydro-1H,4H-pyrazolo[3,4 -d][1,3]oxazine derivatives in good to excellent yields by treatment of pyrazol-amines with aqueous formaldehyde in the presence of acetic acid is provided. The reactions proceeded through an intramolecular etherification process by dehydration of a 1,5-diol intermediate formed in the course of the reaction and promoted by acid media.