The present invention relates to 6, 6 a -dihydrofuro[3, 2- b ]furan-2-(5 H )one derivatives having a formula of structure (A) wherein R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are defined as set forth in the description, and to pharmaceutically acceptable salts thereof, for use in medicine, in particular as antitumour compounds. The invention also relates to a process for preparing the aforesaid compounds which comprises a double cyclisation reaction of 4-in-1, 3-diol organic substrates with the incorporation of a molecule of carbon monoxide, catalysed by a palladium halide in the presence of potassium iodide. Furthermore, the invention is aimed at 6, 6a-dihydrofuro[3, 2-b]furan-2-(5 H )one derivatives having a formula of structure (A), wherein R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are defined as set forth in the description, wherein, when R 1 is methyl or hydrogen, R 2 is selected from the group consisting of alkyl, aryl and heteroaryl.